MACHINE TOOL SPINDLE BEARING

SELECTION & MOUNTING GUIDE

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Content

Introduction ........................................................................... 4
Upgrading
Bearing Selection Overview ......................................................................... 54
NSK Super Precision Bearings – Product Range ........... 6 Robust Design................................................................. 56
Overview ........................................................................... 9 › Angular Control .................................................. 56
Identification Markings ...................................................12 › Cylindrical Roller Bearings ................................ 57
Contact Angle ..................................................................14 Bearing Material ............................................................. 58
Universal Sets ..................................................................16 Sealed Bearings.............................................................. 59
Precision Grades..............................................................17 Sealed TAC ......................................................................61
Preload - Angular Contact Bearings ..............................18 Hybrid Bearings .............................................................. 63
Preload - Cylindrical Roller Bearings ............................ 22 TYN Cages ....................................................................... 64
Bearing Matching ........................................................... 24 TAC Conversions ............................................................. 65
TB Cages.......................................................................... 66
Pre-Mounting
Cleanliness and Washing............................................... 26 Supplementary Information
Greasing Process ............................................................ 28 Bearing Interchange Guide ........................................... 68
Grease Quantities ........................................................... 29 Bearing Failure and Countermeasures ......................... 70
Component Checks ........................................................ 30 Trouble Shooting ............................................................ 75
Bearing Preload Conversion Tables .............................. 78
Mounting › Standard Angular Contact ................................. 78
Fitting Bearings to Shaft ...............................................32 › Robust Series ..................................................... 82
Locknut Torques / Spindle Runout Checks.................. 34 Bore and OD Matching Chart ........................................ 84
Mounting Tapered Bore Roller Bearings...................... 38
› Calculation Method ........................................... 38 Useful Tips ........................................................................... 87
› Gauge Method ................................................... 42
Classical Spindle Arrangements ................................... 44 Index ..................................................................................... 88
Summary of Spindle Arrangements ............................ 45
› Heavy Duty Spindle........................................... 46
› Medium to High-Speed Spindle....................... 47

Post-Mounting
Preload Checks ............................................................... 48
Alignment and Balance ................................................. 50
Bearing ‘Run-in’ Procedures...........................................51
Trouble Shooting ............................................................ 52
› Cause of High Temperature.............................. 52
› Cause of Noise ................................................... 53

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 1

As one of the world’s leading manufacturers of rolling bearings, linear technology
components and steering systems, we can be found on almost every continent – with
production facilities, sales offices and technology centres – because our customers
appreciate short decision-making channels, prompt deliveries and local service.

Europe

Asia
The Americas

Oceania
Africa

The NSK company

NSK commenced operations as the first Japanese network. Here we concentrate not only on the
manufacturer of rolling bearings back in 1916. Ever development of new technologies, but also on the
since, we have been continuously expanding and continuous optimisation of quality – at every process
improving not only our product portfolio but also our stage.
range of services for various industrial sectors. In this
context, we develop technologies in the fields of Among other things, our research activities include
rolling bearings, linear systems, components for the product design, simulation applications using a variety
automotive industry and mechatronic systems. Our of analytical systems and the development of different
research and production facilities in Europe, Americas steels and lubricants for rolling bearings.
and Asia are linked together in a global technology

2
Partnership based on trust –
and trust based on quality

Total Quality by NSK: The synergies of our global network of NSK Technology Centres.
Just one example of how we meet our requirements for high quality.

NSK is one of the leading companies with a long tradition in of quality based on the integrated technology platform of
patent applications for machine parts. In our worldwide tribology, material technology, analysis and mechatronics.
research centres, we not only concentrate on the development More about NSK at www.nskeurope.com or call us on
of new technologies, but also on the continual improvement + 44 (0) 1 636 605 123

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 3

Introduction

The successful build of a spindle will depend on close attention to details as illustrated below:

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Pre-test Checks q an ing Fitting Bearings
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Trouble Shooting d An Ve
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Fa gh rki
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Bearing selection
No ac
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4
Machine Tool Precision bearings are very accurately engineered components and as such
are very important to the successful performance of the machine tool. The way in which
a bearing is handled and fitted to a machine tool does not only determine if the machine
operates accurately but can also affect the life of the bearing in the spindle.

This catalogue is intended to be a comprehensive guide A further section called Upgrading is included to explain
to anyone who fits bearings to a machine tool regardless how to improve both the performance and most of all
to whether it is in planned maintenance or reactive to a the reliability of a spindle. In nearly all cases this can be
breakdown. This catalogue follows a logical progression simply done by replacing the bearing and no changes being
through selection of the correct bearing types, to the necessary to the actual spindle design.
importance of cleanliness before attempting to assemble the
spindle. A detailed part of assembly procedures is included Some sections include a useful tip like the one shown below,
with many photographs and drawings. Pre-test checks, these tips are based on many years of experience and can be
‘running in’ and trouble shooting is also included to allow the particularly useful for newcomers to the spindle repair business
builder more scope in solving spindle problems. and a good reminder to the more experienced engineers.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 5

Bearing Selection
NSK Super Precision Bearings –
Product Range

Several types of Super Precision Bearings are available from NSK. These include
the ROBUST series of high performance bearings, special series of bearings for
unique and specialised applications, and the standard series bearings.

NSKHPS High Precision Angular Contact Ball Bearings

Basic Super Precision Bearings manufactured to conform to ISO standards.
› 70xx, 72xx, 79xx series
› Contact angles: 15˚ (C), 25˚ (A5), 30˚ (A)
› Cage design: phenolic (TR) or polyamide (TYN), depending on application requirements
› Ball material: steel, ceramic (SN24)

Standard Series

Sealed Angular Contact Ball Bearings

Pre-greased and sealed to reduce handling problems. Suitable for maintenance of machine tool spindles.
› Standard series super precision angular contact ball bearings
› ROBUST series high-speed angular contact ball bearings
› Bore size range: ø30–100 mm in ISO series 10 and 19 (70xx and 79xx)

Special Series

Double Row Cylindrical Roller Bearings

Designed to deliver high rigidity in high-speed applications such as lathe spindles.
› Cage material: brass (MB), PPS resin (TB)
› Standard specification E44: Outer ring oil holes and groove

Standard & High Rigidity Series

High Precision Angular Contact Ball Bearings

Suitable for high-speed and high precision motors.
› Cage material: ball guided polyamide cage (T1X,TYA), inner ring guided phenolic cage (T), selection depends on the
application
› Suitable for silent or low vibration operation

Special Series

6
 Ultra High Precision Angular Contact Ball Bearings
High performance bearings developed specifically for internal grinding or high-speed motor
applications under spring preload.
› Bore size range: ø6–25 mm, contact angle: 15˚
› Ball material: steel (S type), ceramic (H and X type)
› Non separable type
› Universal combinations (DU and SU)

BSR Series

High-Speed Angular Contact Thrust Ball Bearings

High rigidity thrust bearings for lathe applications.
› Contact angles: 30˚ (BAR), 40˚ (BTR)
› Ball material: steel (S type), ceramic (H type)

ROBUST Series: BAR & BTR

Ultra High-Speed Angular Contact Ball Bearings

High performance bearings developed for high-speed operation with low temperature rise.
Suitable for ultra high precision machining applications, and ultra high-speed applications.
› Contact angles: 18˚ (BNR), 25˚ (BER)
› Ball material: steel (S type), ceramic (H and X type)
› Cage design: phenolic (T), polyamide (TYN), depending on application requirements
› ROBUST series also can be used for ultra high speed applications of over 3 million dmn.

ROBUST Series: BNR & BER

Ultra High-Speed Single Row Cylindrical Roller Bearings

High performance cylindrical bearings designed for ultra high-speed applications,
such as machining centre spindles.
› Cage material: brass (MR)(1), PEEK resin (TP)
› Roller material: steel, SHX, ceramic
› Ultra high-speed ROBUST RXH design can be used up to 3 million dmn.
(1) MR cage is used in the standard series

ROBUST Standard Series

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 7

Bearing Selection
NSK Super Precision Bearings –
Product Range

High Precision Angular Contact Ball Bearings - RobustShot Series

Direct oil-air lubrication in order to achieve highest speeds.
› Direct air-oil Lubrication via a through-hole in the outer ring
› Contact angles: 18˚ (BNR), 25˚ (BER)
› Lubrication groove with O-rings in the outer ring
› Hybrid bearings - steel rings, ceramic balls

ROBUSTSHOT Series

NSKHPS Angular Contact Thrust Ball Bearings for Ball Screw Support
High rigidity thrust bearings designed specifically for ball screw support applications in machine tools.
› Contact angle: 60˚
› Can be universally matched to any required rigidity specification or life cycle
› A pre-greased line using special grease is also available
› Can be supplied with contact seals and waterproof grease

Special Series
for Machine Tool Applications

Angular Contact Thrust Ball Bearings for heavy duty Ball Screw Support
The high load capacity design delivers five times the life expectancy compared to ball screw support bearings for
machine tool applications of a similar size. The number of rows can also be reduced.
› Easier handling than tapered roller bearings or thrust spherical roller bearings as a result
of non-separable configuration
› Optimum ball bearing design results in lower rotational torque
› Can be universally matched to any required rigidity specification or life cycle
Special Series
for Injection Molding Machines

NSKHPS BSBD Ball Screw Support Bearings

The double row configuration, enables the bearings to support large axial forces in both directions.
› BSN series withouth flange, BSF series with flange
› Paired types also available
› Contact lip seal - provides good sealing at high speeds

BSN & BSF Series

8
Bearing Selection
Overview

Angular Contact Ball Bearing

Conventional Type 72, 70, 79 Series ROBUST Series, High-Speed Type

70 16 A5 TR V1V DU L P3 80 BER 10 S T V1V SU EL P3

Bearing Series Nominal Bore

Diameter
Bore Number
Bearing Type
Contact Angle BNR: 18° Contact Angle
A = 30° BER: 25° Contact Angle
A5 = 25° BSR: 15° Contact Angle
C = 15°
Dimension Series
Material 10: Same bore diameter, outside
Blank Symbol: Bearing Steel (SUJ2) diameter & width as the 70 series
SN24: Ceramic Balls 19: Same bore diameter, outside
diameter & width as the 79 series
Retainer
TR: Phenolic Cage Material
TYN: Polyamide Cage S: Steel Ball
H: Ceramic Ball
Seal X: SHX rings, ceramic balls
No symbol: Open type
V1V: Non contact rubber seal Retainer
T: Phenolic Cage
Mounting Configuration TYN: Polyamide Cage
SU: Single Universal T42: PEEK Cage
DU: Duplex Universal
DB, DF, DT: Duplex Arrangement Seal
DBD, DFD, DTD, DUD: Triplex Arrangement No Symbol: Open type
DBB, DFF, DBT, DFT, DTT, QU: Quad Arrangement V1V: Non contact rubber seal

Preload Mounting Configuration

L: Light SU: Single Universal
M: Medium DU: Duplex Universal
H: Heavy DB, DF, DT: Duplex Arrangement
Gxx: Preload in Kgf (G5=5 Kgf) DBD, DFD, DTD, DUD: Triplex Arrangement
CPxx: Median Preload in Microns (CP10=10µm) DBB, DFF, DBT, DFT, DTT, QU: Quad Arrangement
CAxx: Median Axial Clearance in Microns (CA15=15 µm)
Preload
Precision Class EL: Extra Light
P4: ISO Class 4 (ABEC7) L: Light
P3: Dimensions - ISO Class 4 Gxx: Preload in Kgf (G5=5 Kgf)
Running Accuracy - ISO Class 2 CPxx: Median Preload in Microns (CP10=10µm)
P2: ISO Class 2 (ABEC9) CAxx: Median Axial Clearance in Microns (CA15=15µm)

Precision Class
P4: ISO Class 4 (ABEC7)
P3: Dimensions - ISO Class 4 Running Accuracy - ISO Class 2
P2: ISO Class 2 (ABEC9)

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 9

 Bearing Selection
Overview

Ball Screw Support Bearings Cylindrical Roller Bearings

BS F 30 80 DDU H P2B DT NN 3 0 17 MB KR E44 CC0 P4

Series Cylindrical
(Ball Screw Support) Roller Designator
NN: Double Row, Inner Ring Guided Rollers
F: Flange type N: Single Row, Inner Ring Guided Rollers
N: No Flange type
Width Series
Bore
Diameter Series
Outer diameter
Bore code
Seal type
Material
Preload Single RS: Bearing Steel (SUJ2) (rings and rolling elements)
row RX: Heat Resistant Steel (SHX) (rings and rolling elements)
Class Iso 2 only RXH: Heat Resistant Steel (SHX) for rings and ceramic rolling elements
No symbol: SUJ2 steel
No symbol: single bearing
DT: paired bearing Retainer
MB: Roller guided machined brass cage (Double Row)
TB: Roller guided PPS resin cage (Double Row)
TP: Outer ring guided PEEK resin cage
MR: Roller guided machined brass cage (Single Row)
Ball Screw Support Bearings
Bore Configuration
KR: Ultra Precision Tapered Bore (1:12)
Blank symbol: Cylindrical bore
30 TAC 62 C DDG SU H PN7C
Lubrication
Bearing Bore* E44: Outer ring with machined lubrication groove and holes
(mm) (Double Row Only)

Bearing Type Radial Clearance

** CC1: Standard clearance for cylindrical bore
Bearing O.D.* (mm) ** CC0: Standard clearance for tapered bore
CCG: Special radial clearance
Internal Design
B: High Capacity and Higher Speed Precision Class
(Replaces “A” type) P2: ISO Class 2 | P4: ISO Class 4

Seal Symbol
No symbol: Open type
DDG – Low friction contacting seal
V1V - Non contact rubber seal

Mounting Configuration
SU: Single Universal
DU: Duplex Universal
DB, DF, DT: Duplex Arrangement
DBD, DFD, DTD, DUD – Triplex Arrangement
DBB, DFF, DBT, DFT, DTT, QU - Quad Arrangement

Preload

Precision Class

* For inch series bearings, the fractional portion of the size is omitted.
** CC0 clearance (NSK’s recommended clearance): CC0 clearance range less than CC1. This range overlaps with the upper values of CC9 and lower values of CC1.
As this clearance is easy for customers to target this range, it is the preferred clearance offered for CRB with taper bore.
CC1 clearance: Matched clearance range greater than CC0. While not the standard, this clearance is most popular in the field.

10
 RobustShot Series

80 BNR 10 H T E34D DB EL + P3 Y3

Example: O-rings
Nominal bore diameter Degree of accuracy
Bearing design Preload
Series option Bearing arrangement
Material ROBUSTSHOT design
Cage

Thrust Angular Contact Ball Bearing

100 BAR 10 S TYN DB L P4A 100 TAC 20D PN7 +L C6

Bearing Bore Bearing Bore

Diameter (mm) Diameter (mm)

Bearing Type Bearing Type

BAR: 30° Contact Angle
BTR: 40° Contact Angle Dimension Series
20D: High-Speed Type
Dimension Series w/Revised Internal Features
10X: Arranged with NN30XX Series
Precision Class
Material PN7: ISO Class 4, O.D. is special
S: Steel Ball | H: Ceramic Ball
Spacer (Inner Ring)
Retainer
TYN: Polyamide Cage Preload Class
C6: Standard Preload for Grease Lubrication
Combination C7: Standard Preload for Oil Lubrication
DB: Back to Back Duplex
TAC size range from 140mm to 280mm.
Preload
L: Standard Preload
EL: Standard Preload for High-Speed Applications
CP: Special Preload
CA: Special Axial Clearance

Precision Class
P4A: ISO Class 4, O.D. is Special
P2A: ISO Class 2, O.D. is Special

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 11

 Bearing Selection
Identification Markings

NSK Precision bearings carry useful information for both the designers and fitters.
The box itself will indicate date codes, serial numbers, bore, outer diameter and
width deviations. This information is also found on the bearing so even if the box is
lost/missing, all the relevant information is still available.

Product Serial Number on page 13 indicates that in this example the bearing inner
Every NSK brand bearing has a unique serial number; this ring bore is 25mm –1 microns i.e. the exact size is 24.999mm.*
enables complete traceability of the product since final The outer ring is 47mm –3 microns i.e. the exact size is
inspection data is stored within NSK records associated with 46.997mm.*. The bearing width is 12mm – 57 microns i.e. the
this number. exact size is 11.943mm.*
* Bearing envelope dimensions found from the global catalogue

Size Deviations
Every precision bearing is 100% inspected and the size f and b
deviations are indicated on both the box and the bearing. The ‘f’ refers to the front face preload step and the ‘b’ refers
The outer ring contains the size deviation of the outer ring OD to the rear face preload step. The value of ‘f’ and ‘b’ are the
and the bearing width deviation respectively and the inner absolute step in microns and is recorded on the box label
ring contains the size deviation of the inner ring bore. rounded to the nearest micron.
This information is also placed on the box. The example box

f Open Face
1 OD Size Deviation 6 Inner Ring ‘High Point’ Marking

2 Width Size Deviation 7 Bearing Designation

3 Product Serial Number 8 Bore Size Deviation

4 Brand 9 Country of Manufacture

5 Vee Marking

4
b
Marked Side of Outer Ring
3

6 Vee Lining – Individual Bearings

2 A single Vee line is placed on the outer diameter of the outer
5
1 ring. The positioning of the Vee serves two purposes:
8
1. The radial position indicates the point of maximum ring
thickness, i.e. the position of maximum outer ring runout.
2. The point of the Vee indicates the open face of the
7 bearing. This is particularly useful when using sealed bearings
since the same size seal is often used on each side of the
bearings making it difficult to see which is the open face.

12
 Examples of matched sets Applied Applied
with overall vee line: Axial Load Axial Load

Front of Front of
Spindle Spindle

D: -3 = Outer Ring OD High Point Marking

d: -1 = Inner Ring Bore
C: -57 = Bearing Width
f: -1 = Front Face Preload
b: -1 = Rear Face Preload

Vee Lining – Bearing Sets

If bearings are ordered in matched sets there will also be
a vee line marked across the complete set as well as the
individual vee line. Bearings used in matched sets should High Point
of Shaft
not be taken out of the sequence of the set.
The direction of the overall vee also indicates the direction
of axial loading; this is important when the bearing
arrangement is non-symmetrical as shown above.

Inner Ring High Point Marking High Point Mark

on Inner Ring
The ‘O’ on the face of the inner ring indicates the position
of the maximum ring thickness i.e. the position of maximum
ring runout. (See 6 on page 12) High Point in Housing

How to use High Point Marking

Optimum running accuracy is achieved when the bearing is
mounted so that the ring high points are directly opposite
(180°) to the high points on the housing and shaft. With
High Point on Ring
regard to the shaft, find the high point using a suitable DTI
(Dial test indicator) and mount the bearing with the inner ring
high point at 180°. With regard to fitting the outer ring into
the housing, mount the outer ring vee mark 180° to the high 1. Useful Tip
point measured in the housing. If it is not possible to measure the shaft and
If the runout of the shaft is measured at 2µm, placing the housing runouts it is advisable to position the bearing
inner ring as shown above can help to reduce the runout high points out of line so as to avoid accidentally
close to zero. The shaft runout is much more important aligning the bearing high points with the shaft high
than the housing runout, which can also be more difficult points thereby increasing
to measure accurately. overall runout.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 13

 Bearing Selection
Contact Angle

A fundamental part of the angular contact bearings is the contact angle. These bearings
can only take axial load in one direction unless they are used in sets (see universal sets).

Loading against the contact angle

Load through the inner ring in the
or on the face of the outer ring will
direction of the contact angle.
cause the rings to be disassembled.

Popular Contact Angles:

x, y Points of Contact
Standard Precision 15°
15 o
Contact Angles 25°
25 o
High-Speed ‘Robust’ 18°
25°
y
x Thrust 30°
40°
x Ball Screw Support 60°
y
As the contact angle increases, the axial load capacity
increases but the speed and life decrease. Angular contact
bearings with small contact angles are more suitable for
high-speeds and radial loads.

Contact Angle -0+

Effect of Contact Angle – Standard Designations
15 o For high-speed products; 18° has been adopted as the
AXIAL LOAD
C
7006 TRSULP3 RADIAL LOAD lowest standard contact angle. This has been shown to
SPEED be more effective at high-speeds in terms of bending
25 o stiffness compared to 15°. An 18° contact angle provides
AXIAL LOAD
7006 A5TRSULP3 RADIAL LOAD better axial stiffness than 15°, but less radial stiffness.
SPEED However, as seen from the spindle diagram, bending
30 o stiffness is more important.
AXIAL LOAD
7006 ATRSULP3 RADIAL LOAD
More popular in Japan
SPEED

14
 15° 15° 15°

18° 18° 18°

Axial Stiffness Bending Stiffness Radial Stiffness

For high-speed applications using motorised spindles, the

Bending Radial
Stiffness Stiffness internal heat generation can be much higher than belt driven
spindles; this can reduce the bearing internal clearance and
sometimes cause failure at high-speed.

For these applications it is more beneficial to select a 25°

contact angle because this has a greater radial internal
clearance (RIC) compared to the 18° contact angle and can
more easily accommodate a reduction in internal clearance
Axial
Stiffness due to thermal movement.

Built-in Motor
Examples of Contact Angle –
High-Speed and Thrust Designations
25BGR10STDUELP2 = 15° Robust High-Speed
Grinding Applications
30BNR10STDBELP = 18° Robust High-Speed
30BER10STDBELP3 = 25° Robust High-Speed
30BAR10STYNDBELP3 = 30° Robust Thrust
30BTR10STYNDBELP3 = 40° Robust Thrust
30TAC62BDFC9PN7A = 60° Ball Screw Support

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 15

 Bearing Selection
Universal Sets

The term universal means that the bearings can be used in any arrangement, tandem,
back to back or face to face.

The preload step is manufactured on the rear face of the

f α inner ring and the front face of the outer ring, both steps are
exactly the same depth therefore the universal bearing can
Back to Back be used in any combination.

Back to Back (DB Arrangement)

The majority of machine tool applications use this type of
Face to Face Tandem arrangement. The preload is produced by the ‘Gap’ (2 x the
f: Offset of Front Face
b
SU = Single Universal Bearing step b) of the inner ring faces being squeezed together by a
b: Offset of Rear Face DU = Duplex Universal Bearing
Universal Bearing DUD = Triplex Universal Bearing locknut on the shaft. This type of arrangement is particularly
f=b QU = Quadruplex Universal Bearing
useful where moment loads are used but the accuracy of the
housing must be high to reduce misalignment.
Other universal bearing combinations are shown below:
Face to Face (DF Arrangement)
This arrangement is often used for ball screw support bearing
DU applications. The preload is produced by the ‘Gap’ (2 x the
Combinations step f) of the outer ring faces being squeezed together by an
end cap in the housing. This type of arrangement is particularly
DB DF DT useful when good alignment cannot be guaranteed between
the housings. This can be the case for Ball Screw Support
DUD
Bearings since ball screws can often be 1 to 5 metres in length.
Combinations
Tandem (DT Arrangement)
This arrangement needs to be used with another bearing or
DBD DFD DTD
set of bearings in the opposing direction in order to produce
a preload (see diagram). Bearings are used in these
arrangements when there is a need for higher stiffness due
to higher axial loads on the spindle.

DBB DFF DBT

QU
Combinations

DFT DTT

16
Bearing Selection
Precision Grades

Bearings are manufactured in different precision grades. The lower P number the smaller
the tolerance and greater the running accuracy.
NSK P5 P4 P3* P2 The table above shows the comparison of different accuracy
British Standards Institution (BS 292) EP5 EP7 - EP9 standards. NSK use the DIN system where P2 is the greater
Anti-Friction Bearing Manufacturers Association
(AFBMA, Standard 20) ABEC5 ABEC7 - ABEC9 accuracy. Additionally NSK have introduced a P3 (same external
International Standards Organisation (ISO 492) Class 5 Class 4 - Class 2 accuracies as P4 but higher internal accuracies, same as P2).
DIN (Deutsche Industrie Norm) P5 P4 - P2
Effects of Internal Tolerances –
* P2 Runout, P4 External Tolerances
Radial and Axial Runouts
P2 and P3 tolerance is the highest internal geometry accuracy;
External Tolerances Nominal Dia this results in the best radial and axial runout values.
Total OD Tolerance P2

Single Micron Grading

P4 & P3
All NSK bearings have single micron grading for bore, OD &
P2
width. This means that the exact dimensions of every bearing
Nominal Bore can be found.
P4 & P3 Total Bore Tolerance

Bearing sets are matched to within 1/3rd of the overall

0 Radial Runout tolerances. This is to enable optimum load sharing when fitted
P2 & P3 to the shaft and housing. P2 external tolerances tend to be
P4 approximately half of P4 and therefore are sometimes used
for random matching. However there is a price penalty for P2
standard.
Axial Runout
P2 & P3
0

P4 Typical Tolerances for 7014 (µm)

P4 P3 P2

Bore 0 to -7 0 to -7 0 to -4

OD 0 to -8 0 to -8 0 to -5

Width 0 to -150 0 to -150 0 to -150

Radial Runout 0 to 4 0 to 2.5 0 to 2.5

Example: Width Size
The bearing on the right (7008CTYNSULP4) Deviation Axial Runout 0 to 5 0 to 2.5 0 to 2.5
has nominal dimensions from catalogue of:

OD = 68mm
Deviation on bearing and box = –4µm
Therefore exact OD = 67.996mm 2. Useful Tip
Bore = 40mm The use of P3 Precision grades is more cost effective
Deviation on bearing and box = –4µ than P2. With single micron grading it is possible to
Therefore exact bore = 39.996 Bore Size
Deviation select the correct bearings for matching into sets.
Width = 15mm
Deviation on bearing and box = –100µm Internal geometry of P3 is the same as P2.
OD Size
Therefore exact width = 14.900mm
Deviation

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 17

 Bearing Selection
Preload – Angular Contact Bearings

The preload between angular contact bearings is achieved by clamping

a pair or multiple number of bearings together.

NSK has 4 standard preload arrangements as shown on left

EXTRA LIGHT (EL) MEDIUM (M) side. This allows greater flexibility in machine design and more
importantly when replacing different brands.

All angular contact bearings need to operate with preload

due to the following reasons:
› Elimination of radial and axial play
LIGHT (L) HEAVY (H) › Increased rigidity
› Reduced runouts, increasing accuracy
› Helps to prevent ball skid at high-speed

There are two types of preloading methods:

1) Constant Pressure (Spring Preload)
This type of preload is primarily use for grinding applications
Constant Pressure Preload (Spring Preload) or very fast machining. The speeds quoted in the catalogue
are all for this type of preload. This preload is achieved
by the use of sets of coiled or weaver disc springs. In the
arrangement (Fig.X), even if the relative position of the
bearings change during operation the magnitude of the
preload remains relatively constant.
Spring Carrier
2) Position Preload (Fixed Preload)
This is the most common type of preload arrangement and
Position Preload (Fixed)
can either be arranged with or without spacers. The main
advantage of this type is that the stiffness (rigidity) is much
higher. However, the speed quoted in the catalogue needs
to be factored according to the amount of preload and
number of bearings in the set.
This information is given in the NSK Super Precision
Spacers catalogue and printed below for reference.

Speed Factor Table

Arrangement EL L M H NSK has the most levels of standard preload available:
EL = Extra light – fastest speed, less rigidity
DB 0.85 0.80 0.65 0.55
L = Light – slightly higher rigidity
DBB 0.80 0.75 0.60 0.45 M = Medium – lower speed, good rigidity
H = Heavy – highest rigidity, lowest speed
DBD 0.75 0.70 0.55 0.40

18
Special Preloads and Axial Clearance Effects of Preload on Bearing Performance
Gxx is special preload (xx is the mean preload in kgf) The amount of preload affects the performance of angular
CPxx is special preload (xx is the mean preload gap in µm) contact bearings. The diagrams below show the effects on
CAxx is a special clearance (xx is measured axial clearance in µm) rigidity, temperature, life and speed (dmn*) for a pair of 7020
with a 15° contact angle.
Special preloads are available on request. In some cases
these are generated as Gxx where xx is the amount of The graphs Axialshow
Rigidity that as the preload level increases, both the Bearing T
Radial Rigidity LIFE
7020_DB (L Preload)
preload force i.e. G5 = 5Kgf. This is mainly used for some axial andLimiting
radialdmrigidity
n Value (stiffness) increase, speed capability
800 100 25
special Ball Screw Support Bearings. Or an axial preload gap reduces and temperature increases.

Bearing Temperature Rise, ˚C

95
700
90 20
is quoted i.e. CP10 = 10µm preload gap. In order 600
to maintain high rigidity, it is necessary to85 sacrifice

Limiting dmn, ×104

Rigidity, N/µm

500
speed. Similarly in order to achieve high-speed it is80necessary 15
400 75
Axial Clearance to sacrifice
300 rigidity. To run at higher than factored catalogue
70 10
65
An axial clearance means that there is no initial preload. speed with heavy preload could lead to thermal instability
200
60 5
100
This type of arrangement is often used when application and premature seizure of the bearing. 55
50
0 0
speeds are high and the bearing inner ring fit is much tighter C (15˚) A5 (25˚) A (30˚) C

than normal, this is to prevent a loss of fit between the inner

ring and shaft due to centrifugal expansion of the inner ring. Effects of Preload on Rigidity and Speed

When the bearing is fitted with the tighter fit the radial Axial Rigidity Bearing T
Radial Rigidity LIFE
expansion of the
Axial bearing due to the fit increases the
Rigidity Bearing Temperature 7020CDB (Contact Angle 15˚)
Limiting dmn Value
Radial Rigidity LIFE
7020_DB (L Preload) 7020_DB (L Preload) 100
amount of preloadn to
Limiting dm a normal level. If an application
Value 1 400 25

Bearing Temperature Rise, ˚C

800 100 25 10 000 000 95
1 200
requires a special CAxx level, it must not be substituted 90 20
Rise, ˚C

95
700
Limiting dmn, ×104

1 000 85
Rigidity, N/µm

90 20
Rolling Fatigue Life, h

by a standard
600 E, EL, M or H level preload and run at the
Limiting dmn, ×104

85 80 15
800
Rigidity, N/µm

Bearing Temperature

1 000 000
500 75
same speed, this could cause premature seizure. 80 15
600 70 10
400 75
70 400
10 65
300
65 100 000 60 5
200 200 55
60 5
100 55 0 50 0
L Preload M Preload H Preload LP
0 50 0 10 000
C (15˚) A5 (25˚) A (30˚) C (15˚) A5 (25˚) A (30˚)

Axial Clearance (CA) Effects of Preload on Temperature and Life

+ a Axial Rigidity
Radial Rigidity
Axial Rigidity Bearing Temperature 7020C_L (Preload)
Limiting dmn Value
Radial Rigidity LIFE
7020CDB (Contact Angle 15˚) 7020CDB (Contact Angle 15˚)
1 600
Limiting dmn Value
1 400 100 25 1 400 10 000 000
Bearing Temperature Rise, ˚C

95
1 200 1 200
Rigidity, N/µm

90 20
Rolling Fatigue Life, h

1 000
Limiting dmn, ×104

1 000 85
Rigidity, N/µm

1 000 000
80 15 800
800
75 600
600 70 10 400
65 100 000
400
200
60 5
200 55 0
Single Row DB DBD
0 50 0 10 000
L Preload M Preload H Preload L Preload M Preload H Preload

– a SPINDLE BEARING SELECTION & MOUNTING GUIDE 19

MACHINE TOOL
Axial Rigidity
Radial Rigidity
7020C_L (Preload)
 Bearing Selection
Preload – Angular Contact Bearings

Bearing Combinations
Axial Rigidity Bearing Temperature
Radial Rigidity
Limiting dmn Value
Angular contact bearings are usually used LIFE
7020_DB (L Preload) as multiple bearing
7020_DB (L Preload) Preload=500 N
800
sets. Two rows, three95rows and four rows are the most
100 25 10 000 000
Bearing Temperature Rise, ˚C

700
common multiple bearing 90
sets. 20

Rolling Fatigue Life, h

600
Limiting dmn, ×104

85
1 000 000
500
Bearings are used in multiples80
75
to increase15 the load carrying
250 N 250 N 500 N
400
300 and stiffness capability.70When the number of 10 rows is increased,
100 000
65
200
the rigidity and the load 60 capacity become5 larger but the
100 55
0 limiting speed is reduced. 50 0 10 000
C (15˚) A5 (25˚) A (30˚) C (15˚) A5 (25˚) A (30˚)
Depending on the arrangements, loads can be taken from
either one or both directions.
GC-5-10
The DT arrangement can only take load in one direction but In the example of three rows, it can be seen that the internal
Axial Rigidity Bearing Temperature
Radial Rigidity
Limiting dmn Value
since
7020CDB there
(Contact Angle are
15˚) two bearings with the contact 7020CDB
LIFE
angle(Contact
in the Angle 15˚) preload is not shared evenly, this means that one bearing
400
same direction, it has 95twice the axial stiffness
100 25
as a single is10taking
000 000
twice the preload of the pair and will operate at a
Bearing Temperature Rise, ˚C

200
row bearing. A set of 90 four bearings arranged
20
symmetrically, slightly higher temperature. For this reason, it can be seen
Rolling Fatigue Life, h
Limiting dmn, ×104

000 85
1 000 000
800 could take loads in both 80
75
directions and have
15 twice the axial from the Speed factors table (page 18), that the speed
600
stiffness in both directions. 70 10 capability
100 000
of a set of three is less than a set of four. Load can be
400 65

200
*dmn = the bearing mean diameter
60 (mm) x the speed5 in rpm applied from either direction but greater load from the left side.
55
D+d
0 mean diameter = where
50 D = OD and d = bore0 10 000
L Preload M Preload 2
H Preload L Preload M Preload H Preload

Axial Rigidity
Capacities and Rigidities for Multiple Bearings
Radial Rigidity
Limiting dmn Value
7020C_L (Preload) The single row capacities are shown in the NSK Super
130
1 600
Precision catalogue for all products.
1 400 120
1 200
Limiting dmn, ×104
Rigidity, N/µm

110
1 000
800 100
The table below shows the multiplying factors for both the
600 90 dynamic (Cr) and static (Cor) bearing capacities:
400
80
200
70
Double row Triplex row Quadruplex row
0
Single Row DB DBD DBB

Cr Cor Cr Cor Cr Cor

1.62 2 2.15 3 2.64 4

The NSK Super Precision catalogue also states the preload

and axial rigidity for pairs of all products. This information is
useful when testing a newly assembled spindle. The radial
rigidity can be simply calculated by using the factors in the
table below i.e. for Light preload and 15° contact angle,
multiply axial stiffness given in the catalogue by 6 to get
DB DB DT DT the radial stiffness.

GC-5-9
GC-5-9

20
Calculation of Radial Rigidity
EL L M H
To find the preload and axial rigidity for 3 and 4 rows
15º 6.5 6.0 5.0 4.5
of bearings, multiply the values given in the catalogue
18º 4.5
by the factors in the table right.
25º 2.0

30º 1.4
Stiffness and Preload for Sets
40º 0.7
Likewise multiply the value of radial stiffness found in
the table above by the factor in the table to the right.
To derive the radial stiffness for three or four bearings in DBD DBB

a set, i.e. if the catalogue axial rigidity was 200N/µm for Preload factor 1.36 2
15°, Light preload; the radial rigidity for a set of 3 would Axial rigidity 1.48 2
be 200x6x1.54 = 1848N/µm. Radial rigidity 1.54 2

3. Useful Tip If a 7906CTRDUHP4 is required but only 7906CTRDUMP4

In an emergency situation, if the correct preloaded is available, the spacer can be machined to compensate
bearing is not available and spacers are used, it is for the different preload. From the table above for 30mm
possible to use a different preload set of bearings bore the Heavy preload axial clearance is 16µm and
and adjust the spacers to compensate. The NSK Super the Medium preload axial clearance is 9µm. Therefore
Precision catalogue shows the axial clearances for each to change from Medium preload to Heavy preload it is
set of angular contact bearings. necessary to change the spacer length by the difference
i.e. 16µm – 9µm = 7µm. In this case because we are
Example: increasing the preload we need to reduce the inner ring
Preload and rigidity spacer by 7µm and leave the outer spacer untouched.
Preload and Rigidity (DB and DF Arrangement) Calculation of radial rigidity
Multiply axial rigidity by factors
Table A EL L M H This information can be found on global catalogue pages 156 to 166 for
High Precision Angular Contact Ball Bearings
in table A. 15˚
18˚
6.5 6.0 5.0
4.5
4.5
your reference.
25˚ 2.0
(Standard series) 30˚ 1.4
40˚ 0.7

79 series, C angle
Nominal contact angle 15 Steel ball and Ceramic ball ✽

Nominal EL L M H
Bore Number Bearing Bore Preload Axial Rigidity Preload Axial Rigidity Preload Axial Rigidity Preload Axial Rigidity
(mm) (N) (N/µm) (N) (N/µm) (N) (N/µm) (N) (N/µm)
00 10 7 (5) 10 15 (2) 14 29 (± 1) 19 59 (± 6) 27
01 12 8.6 (4) 12 15 (2) 16 39 (± 3) 24 78 (± 8) 34
02 15 12 (3) 14 25 (0) 20 49 (± 4) 26 100 (± 11) 38
03 17 12 (3) 15 25 (0) 20 59 (± 5) 30 120 (± 12) 43
04 20 19 (1) 19 39 (± 3) 26 78 (± 8) 35 150 (± 15) 48
05 25 19 (1) 21 39 (± 2) 28 100 (± 9) 43 200 (± 17) 61
06 30 24 (0) 25 49 (± 3) 33 100 (± 9) 45 200 (± 16) 65
07 35 34 (2) 29 69 (± 2) 39 150 (± 9) 55 290 (± 18) 78
08 40 39 (1) 32 78 (± 3) 42 200 (± 12) 63 390 (± 22) 88
09 45 50 (0) 37 100 (± 5) 50 200 (± 12) 66 390 (± 21) 94
10 50 50 (0) 39 100 (± 4) 51 250 (± 14) 78 490 (± 24) 111
11
12
55
60
60
60
(± 1)
(± 1)
45
46
120
120
(± 6)
(± 5)
58
60
290
290
(± 15)
(± 14)
90
93
590
590
(± 26)
(± 25)
127
128 Spacers
13 65 75 (± 2) 53 150 (± 7) 71 340 (± 16) 104 690 (± 27) 146
14 70 100 (± 4) 59 200 (± 10) 79 490 (± 22) 119 980 (± 35) 168
15 75 100 (± 4) 61 200 (± 10) 88 490 (± 21) 120 980 (± 35) 171
16 80 100 (± 4) 62 200 (± 9) 80 490 (± 21) 124 980 (± 34) 173
17 85 145 (± 6) 73 290 (± 13) 97 640 (± 25) 138 1 270 (± 41) 191
18 90 145 (± 3) 79 290 (± 9) 102 740 (± 23) 156 1 470 (± 39) 219

Rule:
19 95 145 (± 3) 81 290 (± 9) 105 780 (± 24) 165 1 570 (± 40) 231
20 100 195 (± 5) 83 390 (± 13) 112 880 (± 27) 164 1 770 (± 46) 231
21 105 195 (± 5) 86 390 (± 13) 116 880 (± 27) 167 1 770 (± 45) 235
22 110 195 (± 5) 89 390 (± 13) 120 930 (± 27) 173 1 860 (± 45) 244

The values in ( ) show measured axial clearance To increase preload: reduce inner ring spacer
24 120 270 (± 8) 102 540 (± 17) 135 1 270 (± 35) 200 2 550 (± 56) 278
26 130 320 (± 10) 108 640 (± 20) 148 1 470 (± 38) 214 2 940 (± 61) 302 245.434
28 140 320 (± 10) 111 640 (± 19) 150 1 470 (± 37) 218 2 940 (± 60) 309
30 150 395 (± 7) 124 790 (± 18) 166 1 790 (± 38) 239 3 560 (± 63) 334

To reduce preload: reduce outer ring spacer

32 160 425 (± 8) 134 855 (± 19) 179 1 930 (± 39) 258 3 840 (± 64) 361
34 170 485 (± 9) 151 970 (± 20) 200 2 180 (± 40) 288 4 310 (± 65) 403
36 180 595 (± 12) 158 1 190 (± 25) 211 2 650 (± 48) 302 5 340 (± 78) 425
38 190 605 (± 12) 162 1 210 (± 25) 217 2 790 (± 49) 315 5 600 (± 79) 443
40 200 785 (± 16) 183 1 570 (± 31) 244 3 570 (± 58) 352 7 110 (± 92) 493

79 series, A5 angle
Nominal contact angle 25 Steel ball and Ceramic ball ✽

Remember:Nominal
this is for emergency
EL situations
L only, if the preload
M is changed
H in this way care should be taken to document the changes so that if the bearings are replaced in
Bore Number Bearing Bore Preload Axial Rigidity Preload Axial Rigidity Preload Axial Rigidity Preload Axial Rigidity

the future the correct preload is selected to allow for 49the

00
(mm)
10
(N)
9.8 (2)
(N/µm)
24
(N)
(±spacer
3) 44 changes.
(N)
(N/µm)
20
(N)
100 (1)
(N/µm)
(± 6) 31
(N/µm)
59
01 12 16 (1) 32 29 (± 1) 40 59 (± 3) 52 120 (± 7) 70
02 15 16 (1) 33 39 (± 1) 46 78 (± 4) 60 150 (± 9) 78
03 17 19 (1) 34 39 (± 1) 46 78 (± 4) 62 150 (± 8) 81
04 20 29 (0) 43 59 (± 3) 60 120 (± 6) 75 250 (± 12) 103
05 25 34 (± 1) 56 69 (± 3) 70 150 (± 7) 95 290 (± 12) 123
06 30 39 (± 1) 61 78 (± 3) 77 150 (± 6) 99 290 (± 11) 131
07 35 50 (0) 70 100 (± 3) 94 250 (± 8) 127 490 (± 15) 170
08 40 60 (± 1) 72 120 (± 3) 97 290 (± 9) 139 590 (± 16) 182
09 45 75 (± 1) 87 150 (± 4) 114 340 (± 10) 160 690 (± 17) 207
10 50 75 (± 1) 94 150 (± 4) 124 390 (± 10) 175 780 (± 18) 235
11 55 100 (± 2) 112 200 (± 5) 144 440 (± 11) 198 880 (± 18) 263
12 60 100 (± 2) 117 200 (± 5) 150 440 (± 10) 198 880 (± 18) 267
13 65 100 (± 2) 125 200 (± 5) 161 490 (± 11) 223 980 (± 18) 289
14
15
70
75
145
145
(± 3)
(± 3)
138
142
290
290
(± 7)
(± 7)
183
188
690
740
(± 14)
(± 15)
249
267
1 370
1 470
(± 24)
(± 24)
334
347MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 21
16 80 170 (± 4) 156 340 (± 8) 203 780 (± 15) 274 1 570 (± 25) 367
17 85 220 (± 5) 172 440 (± 9) 229 980 (± 17) 306 1 960 (± 29) 402
18 90 245 (± 4) 188 490 (± 8) 253 1 080 (± 16) 340 2 160 (± 27) 449
19 95 245 (± 3) 195 490 (± 8) 262 1 180 (± 17) 363 2 350 (± 28) 475
20 100 295 (± 5) 197 590 (± 10) 266 1 270 (± 19) 346 2 550 (± 31) 463
 Bearing Selection
Preload – Cylindrical Roller Bearings

In order for machine tool spindles to have high running accuracy and rigidity, cylindrical
roller bearings should be operated with either controlled radial clearances or preload.

Radial Play Roller bearings are supplied with standard RIC

(Radial Internal Clearance) values:
CC1 for cylindrical bores, CC0 for tapered bores
CC9 is a reduced clearance for tapered bores when
used with light fits (non standard). This should not be
Radial used in high-speed since the fit may not be adequate.
Internal
Clearance
(RIC)
The clearance/preload of a tapered bore bearing can easily
Clearance Preloaded
be changed in-situ by pushing the bearing up the 1:12 taper.
The dial gauge can only indicate the clearance situation.
Dial Gauge To apply a radial preload it is necessary to use a special NSK
Block Gauge
gauge or follow the technique outlined in Mounting Section.

Mounting by
lightly tapping
the spacer

GC-6-30

22
Bearing Rigidity Reasons for Using Preloaded Conditions
0.0012
Bearing: NN3020MBKR If the cylindrical bearing is run with a clearance, only a small
Radial load: 1 000 N
0.0010 proportion of the rollers will carry the radial load. This proportion
Radial displacement, mm

0.0008 increases as the clearance is reduced to zero. However when

0.0006
Preloaded, it can be seen that all the rollers are under load,
0.0004
this helps to increase life and also increases the bearing
radial stiffness.
0.0002

0
± 0.008 ± 0.006 ± 0.004 ± 0.002 0 0.002 0.004 0.006 0.008 Amount of Preload
Radial clearance, mm
Tests have shown that the optimum amount of preload is
between zero to 3µm tight for the front roller bearing and a
Life Ratio1.2
Bearing: NN3020MBKR
slight clearance (-2 to -5µm) for the rear roller bearing. The
Radial load: 1 000 N
1.0 graph below shows the bearing rigidity for clearance (right
0.8 hand side) and preload (left hand side).
Life ratio

0.6

The life relationship between clearance and preload can

0.4
be seen below. The values will vary for different sizes of
0.2
bearings but will be the same trend.
0
± 0.008 ± 0.006 ± 0.004 ± 0.002 0 0.002 0.004 0.006 0.008
Radial clearance, mm

Thrust angular contact bearing.

Front: Double row tapered bore cylindrical roller bearing. Rear: Double row tapered bore cylindrical roller bearing.
Usually preloaded. Usually slight clearance.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 23

 Bearing Selection
Bearing Matching

The adjacent bearings in the set are selected in the factory

Bearing Matching Chart
(When bearings are ordered in defined sets i.e.) so that the maximum difference in bore or OD tolerance is
within one third of the overall size tolerance. This is to ensure
-3
DU -1
that once the bearings are fitted to the shaft and in the
housing that the fits from bearing to bearing are fairly similar
DUD and thereby the load distribution within the bearing set is
shared equally.
QU
All NSK bearings are 100% inspected and the bore and OD
size deviation in microns is marked on both the bearing and
the box. For designers this is a useful feature since it allows
NSK Super Precision Ball Bearings
the shaft and housing to be made to suit the bearings. For
79** 79
the example shown above the bore of the inner ring has a
Permissible difference of OD
in a matched set (μm)
P2
P3
The bearings are graded with the deviation in microns
deviation from nominal of -1 micron. If this inner ring was
P4
from the nominal size.
Permissible difference of bore
in a matched set (μm)
P2
P3
Nominal
nominally 70mm diameter then the exact bore diameter will
P4

be 69.999mm.
70** 70 Permissible
P2 difference
Permissible difference of OD from nominal
P3 dimensions
in a matched set (μm)
P4

Permissible difference of bore

in a matched set (μm)
P2
P3
For repair shops this information is even more valuable
Nominal
P4

since it allows greater flexibility when ordering bearings and

enables different combination arrangements to suit different
Bore & OD matching chart
spindle designs.
72** 72 Universal bearing matching
P2 Super Precision ball bearings are made in accordance
Permissible difference of OD
P3 with the International Standards Organisation’s
in a matched set (μm)
P4
dimension plans. All bearings in a set must be within
P2
Permissible difference of bore permissible bore & OD deviation from nominal
P3
in a matched set (μm)
P4 dimensions. This improves load sharing when bearings
are mounted closely.
73** 73 NSK provide a handy sliding chart that enables bearings to be
P2 The size difference of the OD and bore of sets of

easily matched into appropriate sets. First select the series

Permissible difference of OD
P3 bearings is generally less than 1/3 of the size deviation.
in a matched set (μm)
P4
This chart can be used to identify the permissible
P2
Permissible difference of bore
in a matched set (μm)
P3
P4
difference between OD’s and bores in a set of bearings
for precision grades for P2, P3 and P4. i.e. 73xx, 72xx, 70xx or 79xx and then the precision grade, P2,
P3 or P4 and slide the chart to the appropriate bearing size to
find the allowable difference in inner ring size deviation for
each bearing in the set and independently for the outer ring
NSK Super Precision Ball Bearings
OD for each bearing in the set.
79** 79
P2

The examples on left show that for a large bearing a greater

Permissible difference of OD
P3
in a matched set (μm) The bearings are graded with the deviation in microns
P4
P2
from the nominal size.
Permissible difference of bore
in a matched set (μm)
P3
P4
Nominal tolerance between bearings in each set can be used. In
70** 70 Permissible
general most bearings can be matched within 2 microns to
P2 difference

give optimum load sharing.

Permissible difference of OD from nominal
P3 dimensions
in a matched set (μm)
P4
P2
Permissible difference of bore
P3
in a matched set (μm) Nominal
P4

Bore & OD matching chart

72** 72 Universal bearing matching

P2 Super Precision ball bearings are made in accordance
Permissible difference of OD
P3 with the International Standards Organisation’s
in a matched set (μm)
P4
dimension plans. All bearings in a set must be within
P2
Permissible difference of bore permissible bore & OD deviation from nominal
P3
in a matched set (μm)
24 P4 dimensions. This improves load sharing when bearings
are mounted closely.
73** 73
P2 The size difference of the OD and bore of sets of
Permissible difference of OD
 It can be seen that it would be very expensive to stock
Some Possible Spindle Arrangements
every combination of different spindle arrangements. With
the use of the single micron grading the repairer only need
to stock a suitable number of either SU’s or DU’s and the
correct number of bearings can be assembled together by the
repairer as long as the bore and OD deviations are within one
third of the overall bearing tolerance.

Nominal OD Diameter 1/3rd Tolerance Bands

Total OD Tolerance

Nominal Bore Diameter

1/3rd Tolerance Bands Total Bore Tolerance

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 25

 Pre-Mounting
Cleanliness and Washing

In order to obtain the optimum performance from spindle bearings it is necessary to ensure
that the environment in which they are fitted is of the best possible cleanliness condition.

Ideal Spindle Room The washing solutions for bearings should be finely filtered
to at least 5µm and any air supply needs to be filtered with
Work Bench Work Bench appropriate de-humidifiers to prevent water contamination.
Tools should be clean at all times when assembling bearings
and free of burrs that could cause damage to the bearings
Tools Press etc

Tools Press etc

Dismantling Bearing Fitting whilst fitting.

Area Area

Contamination
1st Wash Final Wash Precision bearings are made to very exacting standards with
dimensional and geometrical accuracies measured in microns
and sub-microns respectively. It is important to guard against
Relative Size of Some Contaminates contaminates, hard or soft, entering the bearing during the
fitting process.
The diagram on left side shows the relative size of various
Cross-Section of a Hair 60µm contaminates, all of which could cause problems if entering
the bearing. Metallic debris would usually be much larger
Finger Print (Grease) 15µm
than the examples shown here. Another useful way to prevent
contamination during fitting is to use sealed bearings. More
Smoke Particle 6µm information on this product range can be found in this
Dust Particle 25µm catalogue (see page 11).

Handling Bearings
Ideally dismantling and assembling of spindles should be Avoid heavy shocks during handling. Shock loads can
separated to ensure no cross contamination. scratch or damage a bearing, possibly resulting in failure.
It is not always practical for some organisations to use the An excessively strong impact may cause brinelling,
ideal model above, below is a list of essential improvements, breakage or cracks.
good improvements and ideal improvements. Depending
upon the organisations current situation the appropriate areas Corrosion Prevention
for improvement can be selected: Handling bearings with bare hands can corrode the bearing
surfaces because of the acidic moisture or other contaminates
1 – Essential on the hands. When handling bearings it is best to wear lint
› Separate wash tanks, Separate work bench free protective gloves.
2 – Good
› Separate tools
3 – Ideal
› Separate room (restricted personnel)

26
Global Packaging Method of Cleaning
When NSK bearings are supplied in the new global packaging 1. Use Kerosene or light oil to clean the bearings.
specification, there is no need to pre-wash the bearings 2. Use separate tanks for first cleaning and final cleaning.
before mounting. (A) Each tank should be equipped with a wire rack to prevent
direct contact of the bearing with any contamination that
The Global packaging has the following features: may have settled at the bottom.
› Low viscosity preservative oil that is chemically compatible 3. In the first cleaning tank (B), avoid rotating the bearings.
with common machine tool bearing greases After cleaning the outside surfaces with a soft brush, move
› VPI (Vapour Phase Inhibitor) impregnated into the nylon the bearings to the final cleaning tank.
polyethylene laminated bag. This gives extra corrosion 4. In the final cleaning tank (C), rotate the bearing by hand
protection very gently. Make sure that the cleaning fluid in the final
› Bearing vacuum packed and heat-sealed for added cleaning tank is kept clean.
protection from the outside environment 5. Remove excess cleaning fluid from the bearing after
cleaning. Allow the bearing to completely dry before
This same packaging method is used for factory-greased applying grease or oil using a lint free cloth.
bearings and all sealed bearings. So there is no need to
pre-clean the bearings before mounting. Bearings using ordinary grease lubrication need to be packed
with grease before leaving open to the environment since
Cases for Cleaning Bearings the metal surfaces will be vulnerable to corrosion at this
In certain circumstances it is necessary to clean bearings stage. (D)
before mounting; this will be the case when:
› Packaging does not conform to the standard described Oil lubricated bearings should be mounted on the machine
above tool taking care not to rotate the bearing. Prior to mounting it
› Ultra-high-speeds are required such as when using some is recommended to lightly coat the inner and outer surfaces
‘Robust’ bearings with a clean light film of oil to assist mounting. (E)
› Roller bearings - particularly need cleaning in order to
remove oil film before measuring and setting the correct
radial internal clearance at mounting

(A) (B) (C) (D) (E)

Note: Once bearings are washed and cleaned, avoid rotation before lubricating since this can cause damage to the
rolling elements and raceways. Additional information can be found on the greasing process on page 28.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 27

 Pre-Mounting
Greasing Process

The greasing process is very important to the successful performance of the bearing.
Extra care needs to be taken to ensure no contamination enters the bearing at this point.

The following is a good practice guide to the greasing of Quantity and Position of Grease in Bearing
bearings: The ideal quantity of grease for a spindle bearing is: 15% of
› Take care to ensure that grease tin lids are always the bearing free volume for angular contact bearings and
replaced after use 10% of the free volume for cylindrical roller bearings. The
› Keep grease tins/tubes in a clean separate store at a exact quantities in cubic centimetres for the complete range
stable temperature of NSK bearings can be found in the table on page 29.
› Label tins/tubes with dates, do not use over three years old
› Use clean spatulas for dispensing grease, ideally use For angular contact bearings with ball guided TYN type cage:
plastic syringes pack the grease evenly between the balls from both sides of
the bearings.

For outer ring guided phenolic type cages pack half of the
quantity between the inner ring OD and cage bore on the
rear side of the bearing and the remaining half between
the cage OD and the counter bore of the front face of the
bearings. For either type cage, rotate the bearing by hand to
spread the grease evenly on the surfaces of the raceways,
balls and cage. (A)

For cylindrical roller bearings:

1. Coat about 80% of the grease quantity around the roller
(B) rolling surfaces taking care not to put too much grease
on the cage bore. (This can cause high temperatures
during start up.)
2. Smooth a thin coat of grease over the rollers including the
roller ends, roller cage contact points and along the face
edges of each cage pocket.
3. Use the remaining 20% of grease to apply a thin film to
Position of grease for outer ring
the raceway surface of the outer ring. (B)
guided phenolic type cages

(A) 4. Useful Tip

Use a syringe to apply the
correct quantity of grease
in the correct position.

28
The Recommendable Grease Quantities for High-speed Spindle Bearings
The greasing process is very important to the successful performance of the bearing. Extra care needs to be taken to ensure no
contamination enters the bearing.
Unit: cc/brg
Bore Bore Angular contact ball bearings: Ball screw support Cylindrical roller bearings:
number diameter 15% of internal free space bearings 50% 10% of internal free space
BNR19, BGR19 BGR10 BGR02 BNR10, BAR10
TAC NN49 NN39 NN30 N10
(mm) BER19, 79XX 70XX 72XX BER10, BTR10
S-quantity X-quantity X-quantity X-quantity X-quantity
X-quantity X-quantity X-quantity X-quantity
5 5 – – 0.03 – – – – – –
6 6 – 0.04 0.07 – – – – – –
7 7 – 0.07 – – – – – – –
8 8 – 0.12 0.10 – – – – – –
00 10 0.06 0.13 0.16 – – – – – –
01 12 0.06 0.14 0.23 – – – – – –
02 15 0.11 0.18 0.29 – 2.20 – – – –
03 17 0.13 0.24 0.41 – 2.20 – – – –
04 20 0.23 0.44 0.68 – 2.20 – – – –
05 25 0.27 0.52 0.85 – 3.00 – – 0.4 –
06 30 0.31 0.69 1.20 0.58 3.20 – – 0.6 0.4
07 35 0.48 0.98 1.70 0.78 3.80 – – 0.8 0.6
08 40 0.75 1.20 2.10 0.92 3.90/8.80* – – 1.0 0.7
09 45 0.83 1.50 2.60 1.20 4.20/9.70** – – 1.3 1.0
10 50 0.91 1.60 3.00 1.20 10.20 – – 1.4 1.1
11 55 1.10 2.40 3.90 1.70 10.20/12.00*** – – 2.0 1.5
12 60 1.20 2.60 4.80 1.80 12.00 – – 2.1 1.6
13 65 1.30 2.60 5.70 1.90 – – – 2.2 1.6
14 70 2.10 3.60 6.50 2.80 – – – 3.2 2.4
15 75 2.30 3.60 7.00 2.90 – – – 3.5 2.5
16 80 2.40 5.10 8.70 3.80 – – – 4.7 3.5
17 85 3.50 5.30 11.00 4.00 – – – 4.9 3.7
18 90 3.60 6.60 13.00 5.50 – – – 6.5 4.5
19 95 3.60 6.80 16.00 5.70 – – – 6.6 4.7
20 100 4.90 7.20 19.00 6.10 – 5.4 4.5 6.8 4.9
21 105 5.10 9.00 23.00 7.60 – 5.6 4.6 9.3 5.9
22 110 5.20 12.00 27.00 9.10 – 5.7 4.8 11.0 7.5
24 120 7.90 12.00 31.00 9.80 – 8.4 6.5 12.5 8.1
26 130 9.00 18.00 34.00 15.00 – 11.0 8.5 18.0 12.4
28 140 9.90 20.00 42.00 17.00 – 12.0 9.3 20.0 12.9
30 150 14.00 25.00 53.00 22.00 – 24.0 14.0 23.0 –
32 160 16.00 34.00 – 26.00 – 20.0 15.0 29.0 –
34 170 14.00 42.00 – 33.00 – 21.0 15.0 38.0 –
36 180 22.00 51.00 – 46.00 – 28.0 23.0 51.0 –
38 190 27.00 47.00 – 50.00 – 30.0 24.0 54.0 –
40 200 39.00 76.00 – 61.00 – 44.0 35.0 69.0 –
44 220 42.00 – – – – – 37.0 – –
48 240 41.00 – – – – – 40.0 – –
52 260 77.00 – – – – – 70.0 – –
56 280 80.00 – – – – – 75.0 – –
Note: Do not operate bearings at full spindle speed when bearings are first installed. It is necessary to run * 40TAC72 and 40TAC90
the grease in, see page 28. The grease quantity of “xxTAC20(29)X(D)” should be the same as the double row ** 45TAC75 and 45TAC100
cylindrical roller bearings, which is assembled with this bearing together. *** 55TAC100 and 55TAC120

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 29

 Pre-Mounting
Component Checks

Some machine fitting can be quite complicated and take in the region of a full shift to
complete. In such cases it is particularly important to check all components during the
fitting process, this can eliminate unnecessary problems at the end of the process when
the machine is commissioned.

The following guidelines will be useful: Runouts Checks

› Both shaft and housings should be checked for flaws or Shaft radial and axial runouts should be checked to ensure
burrs that the bearing has the best possible seating accuracy.
› The dimensions of the shaft outer diameter and housing Ideally the shaft should be measured between accurate
bores should be checked for correct size and fit. centres, however, if this is not possible use a surface plate
(Recommended fits for shafts and housings are given in as shown in figure C.
the Global catalogue). Generally an interference fit is used Typical target values will depend upon the application, in
on the shaft provided the application is inner ring rotating, general a target of 3 to 5 microns would be desirable.
and a clearance fit is used in the housing
› Be careful to check the components in a number of Obtaining runouts of the housing is a little more difficult
positions to check for taper and shape as well as size and although not as important as the shaft can be useful in
(figure A shows a typical method for the shaft and figure B eliminating future errors. Figure D shows a typical set up for
shows the typical method for the housing) obtaining the runout for the housing and cover shoulders.
› When taking any measurements it is important to ensure Typical target values will depend upon the application, in
that the components are in a thermally stable state general a target of 3 to 5 microns would be desirable.

Spacers
Inner ring and outer ring spacers for spindle bearings should
be identical in length. (Any difference will affect the preload).
Ideally they should be machined together to the correct
width. Parallelism errors should not exceed 3microns. (Values
greater than this level can cause enough misalignment to
cause bearing inaccuracies and possible noise).

5. Useful Tip
Try to ensure that all components to be measured
are left in the assembly room for 24 hours before
measuring. This is to allow the parts to equalise
to the room and tool temperature.

30
Fig. A: Shaft Measurements Fig. B: Housing Measurements

Fig. C: Runout of Shaft Shoulder Fig. D: Runout of Housing and Cover Shoulder

Front
Cover

Rotate
cover in
both
cases

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 31

 Mounting
Fitting Bearings to Shaft

There are two main methods of fitting bearings to a shaft are (i.) Press fit, (ii.) Shrink fit.

Press Fit Press Fit

Press fits tend be used for smaller bearings typically less than
30mm bore. It is usual to lightly oil the mating parts in order
to reduce the force required for fitting. When fitting the inner
ring care should be taken to ensure the press force is directed
through the inner ring. In the diagram shown, a hole can be
seen in the pressing piece to allow air to escape.

Cylindrical Roller Bearings

When the bearing is separable, the inner and outer rings can Wrong Method
be mounted on the shaft and into the housing as separate
units. Care should be taken when assembling them both
together to ensure correct alignment so as to avoid scratches
on the contact surfaces.

Expansion Chart
µm
6. Useful Tip
240 A hot air gun can be very useful for directing heat
220
ce

r5 at the inner ring only

n
re

60 C

200
ffe

°
70

°C

(especially for large

di

180
C re

°C
0° tu

50
Bore Expansion

p6
bearings).
=8 era

160 °C
40
ΔT emp

140 C
30°
T

n6
120
100 20°C
m5 This method can also
k5
80 be used to heat a
j5
60
housing before
40
20 inserting the shaft/
80 120 180 250 315 400 500
mm
bearing assembly.
Bore Diameter

32
 Shrink Fit
This is used on larger bearings and requires heating the
inner ring to expand the bore and allow fitting to the shaft
with minimal effort. Care should be taken not to overheat
the bearing and ideally only the inner ring needs to expand.
A maximum of 120° should be applied to the bearing. For a
bore diameter of 80mm, heating the inner ring to 40°C above
the outer ring will expand it by 40µm. (See Expansion Chart).

Hotplate Method
It is recommended that a steel ring is used between the hot
plate and the bearing inner ring in order to conduct the heat
to the inner ring and avoid heating balls, cage, outer ring and
possibly lubricant.

Induction Heater Method

An induction heater is a very convenient method of heating
the inner ring and the temperature can be controlled thereby
preventing overheating of the bearing.

Process
Heat the bearings to required temperature plus 20° to 30° to
allow for cooling from heating device to spindle. After fitting
Spacer
each bearing ensure that an axial pressure is applied while
the bearing is cooling down.
(As the bearing cools it will shrink in both axial and radial
directions therefore without additional pressure the bearing
may not be seated correctly). Allow cooling to room
temperature +5°C before fitting the next bearing.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 33

 Mounting
Locknut Torque / Spindle Runout Checks

Locknut Torque Spindle Checks

It is important to apply the correct locknut torque or clamping It is beneficial to check the spindle at each stage of the
force to enable the preload gap to be closed and to prevent assembly process. After fitting the front bearings and
loosening during operation. It is also important not to use clamping the locknut check spindle radial runout as shown.
excessive force as this can distort the bearing raceways and A target runout value of less than 2µm is recommended,
cause loss of accuracy and possible failure; also if spacers however if application speeds are low, values up to 5µm
are used between the bearings, excessive axial force could are acceptable. Tapping gently on the outer ring end face
squeeze the inner spacer shorter than the outer spacer and can help to adjust the runout.
this would increase the preload.
Using the end cover and a steel ring to support the spindle
on the outer ring face, the spindle can be rotated and a
runout reference taken on the shaft. This should be targeted
to below 5µm.

Inaccuracies in the locknut can cause the shaft and bearing to

bend when tightened. The tip on page 35 shows one method
to reduce this effect.

Variation of bearing outside surface generatrix inclination with

Outer ring face runout with raceway outer ring reference face (Radial runout).

34
 The table below shows both the axial force (useful if using
a hydraulic locknut) and torque for standard locknuts.

Nominal bearing bore Locknut tightening Locknut tightening

(mm) force (N) torque reference (N-m)

20 17

25 4,900 21

30 25

35 57

40 9,800 64

45 72

50 80

55 132

60 142

65 14,700 153

70 166

75 176

80 251

85 267

90 281

95 296

100 19,600 311

105 327

110 343

120 371

7. Useful Tip 130 403

140 649

150 695

160 745
If error is in this
direction 170 29,400 796

180 841

190 886
Gently tapping the nut
200 932
in this position can
reduce the bending 220 –
error 240 –

260 39,200 –

280 –

300 –

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 35

 Mounting
Locknut Torque / Spindle Runout Checks

Assembly into Housing

Care should be taken when assembling bearings into the
housing. Usually a clearance fit is used but if alignment is
not true it could be possible to damage or dismantle a bearing.
Heating the housing using an air gun as described in the Tip
section helps to increase the clearance and avoid this problem.

Back to Back Arrangement

1. Assemble bearing
Locknut
2. Tighten locknut
3. Insert as shown into housing

Face to Face Arrangement

Retaining Cover 1. Press bearings into housing.
2. Secure retaining cover for preloading.
3. Insert shaft into inner ring and tighten bearing locknut.

Retaining Cover Tightening

The bearing rings can become deformed if the retaining cover
GC-6-9
is not secured correctly.

GC-6-10
The example depicted on the left shows the effect of uneven
Retaining Cover Bolts (4 places)
tightening of the retaining cover; in this case only four bolts
Outer Ring
are used and not torqued evenly.

This can cause deformation of the raceway that could lead

1 µm 1 µm

Evaluated Area
to vibration, loss of accuracy and premature bearing failure.
Before Tightening After Tightening (Outer Ring)
Ideally the amount of stick-out or recess depth in the housing
after assembling the spindle should be measured using
a depth micrometer, this enables the correct amount of
squeeze to be set on the retaining cover.
Adjusted
Bolts
Amount
(6 Places)
In the example on the left side six retaining bolts have been
evenly tightened. On the second graph the gap was too big
and this can also cause deformation of the raceway.
1 µm 1 µm
Evaluated Area
(Outer Ring)
Tightening Adjusted by 10 µm Tightening Adjusted by 50 µm

36
 Housing Concentricity
The concentricity of the rear bearing housing can be
measured as shown on the left. This value should be
less than 10µm, ideally target 5µm.

Final runout checks should be conducted on the fully

assembled spindle both radially and axially at the nose
and radially at the rear. Target runout values should
be no greater than 5µm.

1 to 2µm is typical for high-speed spindles.

Nominal Clearance between Clearance between

Nominal
bearing bore retaining cover and retaining cover and
bearing bore (mm)
(mm) housing (mm) housing (mm)
The table shows the correct amount of gap to be left
20 140
to allow the correct squeeze on the retaining cover.
25 150
30 160
35 170
40 180
45 190 0.03
50 200 to
55 220 0.05
60 240
65 0.01 260
70 to 280
75 0.03 300
80 – –
85 – –
90 – –
95 – –
100 – –
105 – –
110 – –
120 – –
130 – –

8. Useful Tip
When assembling cylindrical roller bearings, the outer
ring is first pressed into the housing. Lightly grease or
oil the raceway before inserting the spindle with inner
ring/roller assembly. Rotate the bearing assembly
while inserting, this minimises any damage to the
outer raceway and rollers.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 37

 Mounting
Mounting Tapered Bore Roller Bearings –
Calculation Method

As stated on page 22 the mounted clearance of a cylindrical

roller bearing is very important to the optimum performance of
the spindle. When using tapered bore types it is recommended
D Dh to set to a slight preload at the front of the spindle and a slight
clearance to the rear of the spindle. This procedure can be
easily accomplished with the use of special GN gauges (see
next section).

However, an individual gauge is required for each bearing

size so it is not always practical or economical to have a
gauge available. This section will explain how to set the
required preload or clearance without the use of a gauge.

Step 1
Determine the amount of shrinkage of outer ring raceway
diameter due to fitting in the housing.
∆re (Shrinkage) can be calculated or measured.

Calculation Method
∆re = (Dh – D) x h
(If ∆re >= 0, ∆re = 0)

Dh: Bore diameter of housing

D: Outer diameter of outer ring
h: Reduction factor
(NN30xx, N10 series: 0.62)
(NN39, NN49 series: 0.70)

Measured Method
Ensure that the outer ring and housing are the same stable
Dial Gauge temperature. Using a cylinder gauge measure the bore of
the outer ring in four different places before inserting into
the housing.
rm

Insert the outer ring into the housing and repeat measurements.
Using average measurements calculate amount of shrinkage
(if any) and record.

Rollers Step 2
Inner Ring Outer Ring Determine the initial Radial clearance ∆rm.

GC-6-31

38
 Dial Gauge Remove the oil on the taper surface of the shaft and bore of
Block Gauge
the inner ring. Mount the inner ring assembly and place the
outer ring over the rollers. Apply a dial gauge to the outer
L diameter of the outer ring (*1).

Mounting by Step 3
lightly tapping Lightly tighten the locknut; this will drive the bearing up the
the spacer
1:12 taper and expand the bore to reduce the radial internal
clearance (RIC) of the bearing. Measure the free radial play
by moving the outer ring in a downward and upward motion.
Continue to tighten the locknut (i.e. moving the bearing up
GC-6-30 the taper) until the radial clearance measured is approximately
α
0.005mm (*2).

Taper 1:12 Remarks:

φ d1
φd

(*1) If the measurement takes too long, the temperature of

the outer ring may rise to body temperature resulting
in an erroneous measurement. Wearing gloves is
recommended to reduce heat transfer.
(*2) If there is an excessive amount of play, the outer ring
may have deformed into an ellipse when pressed by
hand. This would result in an erroneous measurement.
B
Therefore, 0.005mm of play is acceptable (0.005mm
is the target value, but 0.001mm to 0.002mm is also
acceptable).

Step 4
When ∆rm is set to approximately 0.005mm, record this value
and measure the distance from the shaft shoulder to the inner
ring end face (distance L) using slip gauges (block gauges).

Care should be taken when using the slip gauges since the inner
ring can be tilted by the action of inserting the slips. Record the
average distance from two to three measurements (*3).

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 39

 Mounting
Mounting Tapered Bore Roller Bearings –
Calculation Method

Step 5
Calculate the required length La for the spacer manufacturing
according to the target clearance or preload required using
Acceptable range Unacceptable range
for inserting
block gauge
for inserting
block gauge
the following formula:

La = L – (K (∆rm - ∆r + ∆re))

GC-6-32
Hollow Shaft Ratio and Coefficient K La: Finish dimension of spacer for setting post mounting
radial clearance
Hollow shaft ratio ko Coeffecient K
L: Width of block gauge
45-55% 14 (measured result from Step 4)
55-65% 15
∆rm: Movement of the outer ring in a radial direction
65-75% 16
(measured result from Step 3)

∆r: Target Radial clearance or Preload after mounting

∆re: Shrinkage of outer raceway diameter due to fitting in

the housing

K: Coefficient (conversion value which includes

shrinkage of a hollow shaft with a 1/12 tapered hole) -
(for solid shaft K = 12)

K0: Hollow shaft ratio = A/B x 100

A: Shaft bore diameter B: Shaft outer diameter

40
 Example of Calculation
L = 20.55
(distance between inner ring and shoulder)
∆rm = 0.007 (measured RIC (Lift))
∆r = -0.002 (required RIC) i.e. preload
∆re = 0.004 (reduction in RIC due to housing)
K = 15 (hollow ratio of shaft is 60%)

La = 20.55 – (15 x ( 0.007 - (-0.002) - 0.004))

(Be careful of sign notation - (-) = +)

La = 20.475mm

If a solid shaft was used the value of K is 12

i.e. 1:12 taper

In this case the La (spacer width) = 20.490mm

Remarks:
(*3) For the measurement of dimension L, the value obtained is
produced by inserting the block gauge in the left half of the
zone shown in Step 5. The right hand side shows that the
gauge cannot be inserted (This is due to tilting that occurs
between the shaft shoulder and inner ring end face.)

9. Useful Tip
The formula can be made simpler by using the solid shaft
coefficient of 12 for all hollow shafts. This would result
α
in a slightly lower preload but is easy to remember from
the taper ratio of 1:12 i.e. for every 12µm movement up
the taper the internal clearance is reduced by 1µm. Taper 1:12
φ d1
φd

In this case using the same values as above but with

K = 12, La = 20.49mm. The difference in radial movement
is only (20.49 – 20.475) / 12 = 1.2µm. This would give
a value of 0.8µm lower than the targeted 2µm preload
B
(this is safer than over preload).

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 41

 Mounting
Mounting Tapered Bore Roller Bearings –
Gauge Method

Mounting of Tapered Bore Cylindrical Roller Bearings – Method

Gauge Method
As stated on page 22 the mounted clearance of a cylindrical Step 1
roller bearing is very important to the optimum performance of Insert outer ring into the housing. (This is usually between
the spindle. When using tapered bore types it is recommended 2µm clearance and 2µm interference.)
to set to a slight preload at the front of the spindle and a slight
clearance to the rear of the spindle. Step 2
This procedure can be easily accomplished with the use of Measure outer ring bore using a cylinder gauge at about
special GN gauges. A GN gauge is an instrument for matching four different locations. Determine the average for the
the tapered section of a shaft to the tapered bore of a bearing measurements and set the gauge to zero. (A)
when mounting a cylindrical roller bearing with a tapered (Confirm that all components, outer ring in housing, inner ring
bore onto a machine tool spindle. After mounting, the GN and shaft, are the same temperature before setting to zero.)
gauge is used for precise control of the bearing’s radial internal
clearance. This instrument is especially effective when a Step 3
cylindrical roller bearing is used with radial preload. Adjust the inscribed diameter of the GN gauge.
The idea is to set the bore of the GN gauge to replicate the
bore of the outer ring after insertion in the housing. (B)
Loosen the bolt of the main body fixture on the GN gauge.
Apply the cylinder gauge to the inscribed diameter surface
Main Body Fixture
Dial Gauge of the GN gauge and adjust the setscrew to the setting of
Gauge Body
the dial on the cylinder gauge to zero (see diagram on the
GN30XX
Handle
left). (Use the GN gauge in an upright position to avoid
inaccuracies due to its own weight.)

Step 4
Gauge correction factor is necessary. Using the pointer control
NIPPON SEIKO
Pointer Control
on the GN guage, adjust the main pointer to the red line on
Setscrew
the front glass of the dial gauge. Confirm that the short needle
is around the 2 position on the secondary dial. (C) (Gauge
correction corrects for elastic deformation of the rollers due to
(A) (B) measuring pressure on the gauge. The amount of correction for
each gauge is determined upon shipment of the gauge.)

Step 5
Mount the cleaned inner ring (not yet greased) onto the shaft
(C) and tighten the shaft locknut lightly.

GC-6-23

(D)

42
 Step 6 Step 8
Expand the GN gauge by adjusting the setscrew by about Widen the GN gauge using the adjusting screw and carefully
0.2 to 0.3mm. Place centrally over the inner ring rollers and lift off the assembly avoiding any impact with the rollers.
release the setscrew to allow the GN gauge to spring closed
over the rollers. (D) Step 9
Measure the clearance between the end face of the roller
Step 7 bearing inner ring and the shoulder of the shaft or dummy
Oscillate the GN gauge lightly in the peripheral direction as spacer. Using block or slip gauges measure the gap around
shown to allow the dial indicator to stabilise. Tighten the shaft the circumference in a number of positions (ideally 4)
locknut until the gauge reads zero. and record the average value. The final spacer should be
manufactured to this length.
Example 1 Example 2

5 0 5 0 0 5 0 5
10 10 10 10

GN30XX

NIPPON SEIKO
Step 10
Remove the locknut and bearing from the shaft. Fit the
adjusted spacer and re-assemble the bearing and locknut.
Reading the Dial Gauge
If the dial needle is in the position clockwise to the zero it Step 11
indicates that there is clearance present. Re-check the value of the clearance/preload by placing the
If the dial needle is in the position anti-clockwise to the widened gauge over the rollers and adjust the screw to
zero it indicates that there is preload present. The actual allow gauge to contact the rollers. Using the guide in step
amount of clearance or preload is ½ the indicator reading. In 7 re-check to ensure that the target values of clearance/
example 1 the indicator reads 2 anti-clockwise. This indicates preload were achieved.
–1µm clearance or 1µm preload. In example 2 the indicator
reads 4 clockwise which equals 2µm clearance. Spacer adjusted to
enable correct setting
Locknut

10. Useful Tip

In the case where a thrust bearing is used adjacent
to the roller bearing, it is better to make an assembly
spacer to incorporate the width of the thrust bearings
for use while setting up. This will prevent damage
pressing the thrust bearings on and off the spindle
a number of times. Inner Ring Assembly Spacer
Assembly

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 43

 Mounting
Classical Spindle Arrangements

Free Side Located Side

A Typical Medium Speed Spindle
› fixed preload › fixed preload
› outer rings allowed to float › outer rings located
Spindle Type:
Type 1

Typical Application(s):
Turning machines and
general machining centres

A Typical Workhead Spindle Note: All bearings are preloaded together i.e. one set.
Both spacers need to be identical in length

Spindle Type:
Type 2

Typical Application(s):
Turning machines and
general machining centres

A Typical High-Speed Spindle

Note: Work end bearing located, preload

Spindle Type: applied through springs at rear bearing
Type 3

Typical Application(s):
High-speed grinding spindle

44
Mounting
Summary of Spindle Arrangements

Confirm Bearing Shaft and Housing Fits

› See NSK bearing box label for exact bearing bore

and OD dimensions to one micron.
› Measure the shaft OD and housing bore at the
bearing locations.
› Calculate the bearing shaft and housing fits and
compare with OEM specifications or NSK guidelines.
› Excessive bearing-shaft interference or insufficient
bearing-housing clearance fit may lead to
excessive bearing preload and seizure.
› Insufficient bearing-housing clearance at the
rear-side may prevent the rear-side bearings
and shaft from floating within housing bore
during axial thermal expansion.

b
D = OD
d = Bore
C = Width

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 45

 Mounting
Heavy Duty Spindle

Cylindrical Roller Bearings (Tool-Sides and Rear-Sides) Thrust Angular Contact Ball Bearings
› Double-row cylindrical bearings (NN3XXX) with tapered bores allow for
› Thrust angular contact ball bearings can
precise setting of internal clearance (between rollers and outer ring bore).
be types BAR (30º) or BTR (40º).
› Check the bearing bore taper against shaft taper for a good match.
› These bearings are designed to take only
› Radial clearance depends on OEM, spindle design, speed, operating
thrust loads due to special OD tolerance.
temperature, etc. (consult OEM specs or NSK guidelines).
› Angular contact bearings with standard OD
Usual to target a 2µm preload.
tolerance may fail.
› Target outer ring to housing fit is 2µm loose to 2µm tight.
› The double-row cylindrical roller bearing
› Tool-Side: Excessive preload (negative radial clearance) can result in high
will support the radial load.
bearing running temperature and seizure.
› Rear-Side: This bearing is usually mounted with greater radial clearance
than tool-side to ensure the shaft floats within housing during axial
thermal expansion. Usual to target a 5µm clearance.

Rear-Side

Tool-Side

Locating Spacers
Tool-Side Labyrinth Seal Clamping Nut
› This spacer is adjacent and forward of the double-
› Most spindle designs should row cylindrical roller bearings (NN3xxx). › Sufficiently tighten clamping nut to prevent
include a labyrinth seal to minimise › Spacer width determines the bearing’s position bearings from backing off.
contamination. along the shaft taper and establishes the mounted › If bearings become loose, the bearing set may
› Labyrinth designs that incorporate an radial internal clearance. lose preload and rigidity, the spindle may not
air barrier should use clean, dry air. › Grind spacer to specific width after setting radial machine properly or it may make noise.
› Avoid aiming coolant directly into internal clearance and before final mounting of › Check shaft-bearing assembly straightness after
spindle nose. NN3xxx bearing. tightening.

46
Mounting
Medium to High-Speed Spindle

Outer Cap Clamping Nut Spacer Rear-Side Angular Contact Ball Bearings

› Most spindle designs include an outer › This spacer in between the › Rear-side bearings and shaft must float within housing bore to
cap whose male register surface should bearing inner ring and clamping allow axial thermal expansion. Therefore, a clearance fit should
lightly compress the bearing’s outer ring. nut (most spindle types). exist between the rear-side bearing OD and housing bore.
› Suggested axial compression: 10-30µm. › Spacer ensures even clamping › Calculate clearance fit with housing bore measurement and
› The male register’s surface should around the bearing’s inner ring. bearing OD from box label.
be flat and parallel to the outer cap › Mating surfaces should be flat › Compare calculated clearance fit with OEM specification or NSK
mounting flange surface that contacts and parallel. guidelines.
the housing. This will ensure even › Spindle rear-side bearings usually have light preload or less.
clamping pressure against the bearing › High-speed spindles may use a single-row cylindrical roller
outer ring. bearing instead of angular contact ball bearings, with a
› Excessive and/or uneven clamping locating outer ring fit, the axial expansion is allowed by roller/
pressure can result in bearing noise or outer bore movement.
loss of preload.

Rear-Side

Tool-Side

Bearing Spacers

› Spacers between bearings increase bending rigidity at the spindle tool-side.

› Spacers may lower bearing running temperature due to separation,
depending on spindle design and operating conditions. Shaft Alignment
› When necessary, bearing mounted preload can be reduced or increased by
› Check shaft straightness at this location relative to
offsetting spacers.
tool-side after final assembly.
› Reducing preload may allow higher spindle speed or lower bearing
› Check spindle alignment with drive source.
operating temperature, especially for grease-lubricated bearings.
› Avoid excessive belt tension for belt-driven spindles.
› Increasing preload can be used to increase spindle rigidity.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 47

 Post-Mounting
Preload Checks

Preload Checking 30
The final preload after assembly is important, factors such as 25 DB Arrangement of
65BNR10STYN
fits, spacer compression, locknut torque and correct seating

Starting Torque, N´ mm
20
can affect the preload. If the final preload is larger than 15
required, the rigidity will be increased, which is a positive
10
aspect, but the temperature will also be increased which
5
could cause a seizure under certain conditions. If the preload
0
is too low, temperature will be lower but there might not be 100 200 300 400 500 600 700
Preload After Mounted, N
adequate stiffness to support external loads.
This method is best suited to applications where the preload
Methods of Checking Preload is high. Most high-speed machine tool spindles use a lower
There are three methods for checking the preload in mounted preload and in this case the error can be large.
angular contact bearings depending on the amount of preload
and accuracy required. 2. Force Deflection Method
For this method a thrust load is axially applied to the spindle
1. Starting Torque Method and its axial displacement is directly measured as shown
This is obtained by measuring the tangential force of the below. The preload is obtained by the relationship between
spindle by either using a spring balance or rotary torque axial displacement and preload, see example graph below:
devise as shown below:

0.025
DB Arrangement of
65BNR10STYN
Axial Displacement, mm

0.02
Rotary Torque Meter Preload after mounted
0.015 250 N
400 N
Housing 550 N
Measurement of 0.01
starting torque
Block 0.005

0
0 500 1 000 1 500 2 000
Axial Load, N

This method is better suited to lower preload applications.

Shaft If the preload is very high it may be necessary to use special
hydraulic equipment to apply a large enough axial load.
For example if the axial rigidity is 200N/µm, an axial load
of 2000N will be required to deflect the spindle by 10µm.
If loads are excessive, elastically deformation can occur in both
Care should be taken with this method
GC-6-19 since oil film the bearing internals and associated machine parts; this could
formation in the ball contact area can cause stick – slip, result in a measured preload being lower than actual value.
this can give a higher than actual value.
The preload is obtained from the relationship between
measured starting torque and preload. An example is
given in the graph on next column:

48
3. Natural Frequency Method Housing

This is by far the most sensitive and repeatable method but Block
the results can be affected by the spindle design and more

Resonance Frequency of Main Shaft, Hz

sophisticated equipment is required to measure the natural Thrust Load Fa
frequency of the shaft assembly.

The shaft is vibrated in the axial direction by lightly tapping Dial Gauge Shaft

with a hammer and measuring the resonant frequency with

Axial Spring Constant, N/µm
an accelerometer coupled to a vibration analyser.
(See diagram to right).
Resonance Frequency of Main Shaft, Hz

The actual preload after mounting can be found by the

Preload After Mounting, N

relationship of resonant frequency (Fz) to axial spring
stiffness of the shaft assembly (Ka) and the relationship
between stiffness and preload.

Natural Frequency Formula Preload Axial Spring Constant, N/µm

Axial Spring Constant, N/µm
In some cases a special hammer containing a transducer can
be used to impact against the shaft assembly, this allows the
impact force to be measured. In this situation the preload
Preload After Mounting, N

can be calculated directly from the formula without the Ka

need of graphs. Fz is found from the spectrum analyser, the Fz = 1 m ×1 000
shaft assembly is weighted (M) and Ka = Force/movement 2π
(movement measured by accelerometer in µm).
Ka : Axial spring constant of bearing (N/µm)

m
W
FzPreload: Axial
m= g
Resonance frequency
Spring Constant, N/µm (Hz)
: Mass of rotating body (kg)
Summary of Methods
The resonant frequency method is not suitable for applications
using bearings with clearances such as N or NN Cylindrical Advantage Disadvantage
roller bearings that are not preloaded.
Not good for light preload.
Starting Used for heavy preload.
Axial Rigidity If starting torque is small,
torque If starting torque is high,
variation of measurement
The axial rigidity can be checked by comparing the values of method measurement error is small.
is large.
deflection obtained i.e. if 10µm deflection is the result of an
axial load of 1000N, the axial rigidity is 1000 / 10 = 100N/µm. Not good for heavy preload.
Values for axial rigidity for pairs of bearings are given in the Thrust static Used for
Loading equipment is too
large scale. Affected easily by
NSK Global catalogue, these values are before mounting and rigidity method light preload.
deformation of contact part
are a guide only; the mounted values will be higher due to other than bearing.
fits and clamping forces etc.
The effects of fits and clamping forces on stiffness can be Natural Measurement Influence of spindle
frequency accuracy is high. fixing condition should not be
calculated by NSK on request.
method Good repeatability. ignored.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 49

 Post-Mounting
Alignment and Balance

Balance Vee Drives

Any unbalance of rotating components will cause repeated Spindle assemblies using V-belts should have the misalignment
stress or excessive vibrations due to centrifugal force. This is between the spindle shaft centre and motor shaft centre less
especially true for spindle rotating at high-speeds i.e. above than 0.1mm.
1 million dmn.

dmn is a speed factor used within the bearing and lubrication

industry and is simply the mean bearing diameter in mm
multiplied by the rotational speed in rpm and is usually
expressed in terms of millions or part millions. EG. A 7014
bearing has a mean diameter of 90mm, if it was operating
at 12000rpm, the dmn would be 90x12000 = 1.08Mdmn, and
classed as high-speed in need of balancing.

Units of unbalance are either expressed in g-mm (gram Couplings

millimetres) or using the ISO or ANSI system a G number, Care should be taken when using direct drive couplings.
which is a vibration velocity expressed in mm/sec For high-speed, special couplings will be necessary.
(millimetres/second). Coupling joints should have the misalignment between
For example, G1.0 corresponds to a free spinning vibration of the spindle shaft centre and motor shaft centre corrected
1.0 mm/sec and is typical for high accuracy grinding machines. to 0.01mm or less.
Remember that both offset and angular misalignment
G Grades can occur with direct drive coupling:
0.4 Gyroscopes, Ultra precision grinders.
1.0 High-Speed grinding machines, jet engines, small high- Off Set Misalingment

speed motor.
2.5 Medium to large electric motors, Machine tool drives.
6.3 General Machine tools, cylinders and rollers for printing
machines. Angular Misalingment

The grades continue up to 4000.

Alignment
There are two basic types of misalignments: angular and Misaligned shafts can result in:
offset. In reality most applications have a combination of › Vibration of the spindle
both. If misalignments are not minimised, the resulting › Increased bearing load
moment loads on the bearing can cause premature failure. › Damage to the bearings
› Poor surface finish of the work
› Increased energy consumption
› Premature bearing failure

50
Post-Mounting
Bearing ‘Run-in’ Procedures

‘Run-in’ Procedures Intermittent Running Procedure

‘Running in’ is very important to the life of the bearings. Intermittent running is a good option if you are short
During this final process of the mounting procedures it will of time. The process works by stopping operation and
help you determine if there are any problems with the stabilising temperatures before there is a rapid temperature
spindle. The ‘run-in’ process is aimed at channelling excess rise, (this being caused by a sudden movement of grease
grease out of the way of the rolling elements. An improper across the path of the balls during operation).
run-in will result in higher than normal temperatures in the
bearing and can ultimately cause early failure of the bearings Procedure
due to the break down of the grease. There are two methods 1. First take the maximum operating speed and divide it into
of the run-in processes; continuous run-in and intermittent eight to ten stages to determine the maximum target
run-in. speed for each stage.
2. Each stage is divided into 10 cycles that are approximately
Continuous Running Procedure one minute long.
Continuous running works by gradually increasing the 3. During each cycle, rapidly accelerate the spindle assembly to
operating speed from the low speed zone. Although the target speed for the current stage, and then decelerate
somewhat time consuming, this procedure helps machine back to zero, and rest for a period i.e. 40 seconds.
operators to detect potential problems related to the main 4. Repeat this cycle about 10 times.
shaft, thus avoiding costly damage to the bearings. 5. Continue moving up through the stages, following the
above procedures, until you reach the target speed. i.e. if
Procedure (This process can take up to 18 hours) the maximum speed is 8000 min-1 the first target maybe
1. Begin at a reasonably low operating speed. 1000 min-1, cycle ten times, and then move to 2000 min-1
2. Monitor for temperature rise. and so on until 8000 min-1.
´ 1 cycle for target speed 2 000 min± 1 (10 cycles per stage; 8 stages per running in)
3. Stabilise the temperature.
4. Continue incremental increases of operating speed n

until reaching maximum operating speeds.

0
2.5 S 15 S 2.5 S 40 S

1 minute of 1 cycle
NN3019 95BT10XDB NN3017 NN3019RIC= -2 microns
NN3017RIC= +3 microns Grease NBU8EP

80
N=3500rpm 11. Useful Tip
60 N=3000rpm NN3019
95BT
N=2500rpm It can be useful to initially run the spindle at a low
N=2000rpm 95BT
Temperature (ë C)

40 speed say 5% of the maximum speed for about 15

N=1500rpm Housing

20
N=1000rpm
N=500rpm
NN3017 Rear
minutes to gently align the grease within the bearing
Ambiant Temperature
and to ensure there are no mechanical problems or
0
loose nuts.
After the ‘running in’ procedure has been completed
0 1 2 3 4 5 6 7 8 9 10 it can also be useful to run for about
Hours
1 hour at the maximum operating speed.
Note: It is very important that if the temperature of the bearings reaches 70°C, or 50°C at
the housing, shut the machine down. These temperatures could cause early failure of the
bearings.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 51

 Post-Mounting
Troubleshooting - Cause of High Temperature

Cause of High Temperature The causes of high temperature can be a number of things
After mounting has been completed, a test run should be ranging from excessive amount of lubricant causing high
conducted to determine if the bearing has been mounted frictional heat due to churning, to insufficient lubricant that
correctly. could cause starvation and high contact friction. In the latter
case it could be some time before the high temperature
It is best to monitor the temperature directly with a thermocouple occurs but in the case of too much lubricant, the high
on the outer ring of the bearing, if this is not possible, then temperature usually appears at the start.
the temperature on the outside of the housing will give a Other causes of high temperature could be insufficient
general indication. bearing clearance, incorrect mounting or excessive friction at
the seals. In the case of high-speed applications, the wrong
The bearing temperature should rise gradually to a steady bearing type, lubricant or lubrication method could lead to
level within one to two hours depending on the size of the abnormally high and unstable temperatures.
equipment and the power consumption after start up. If the
bearing experiences trouble or if there is some mounting Below is a table showing reasons for high temperature,
problem, the bearing temperature may increase rapidly and vibrations, lubricant leakage and the countermeasures.
become abnormally high.

Cause Countermeasure

Excessive amount of lubricant Reduce amount of lubricant or select stiffer grease.

Insufficient or improper lubricant Replenish lubricant or select a better one.

Abnormal Improve the fit, internal clearance, preload, or position of housing

Abnormal load
temperature rise shoulder.

Improve the machining accuracy and alignment of the shaft and

Incorrect mounting
housing, accuracy of mounting, or mounting method.

Correct the seals, replace the bearing, or correct the fitting or

Creep on fitted surface, excessive seal friction
mounting.

Replace the bearing and use care when handling and mounting
Brinelling
bearing.

Flaking Replace the bearing.

Vibration
(radial runout of shaft)
Correct the squareness between the shaft and housing shoulder or
Incorrect mounting
sides of spacer.

Penetration of foreign particles Replace or clean the bearing, improve the seals.

Leakage or discolouration Reduce the amount of lubricant, select a stiffer grease. Replace the
Too much lubricant. Penetration by foreign matter or abrasion chips
of lubricant bearing or lubricant. Clean the housing and adjacent parts.

52
Post-Mounting
Troubleshooting - Cause of Noise

Cause of Noise Possible causes of noise include: incorrect lubrication, poor

Acoustic or other instruments can check bearing noise. alignment of the shaft and housing, or external contamination
Abnormal conditions are indicated by a loud metallic entering the bearings. Below is a chart of possible causes and
noise or other irregular noises. countermeasures:

Irregularities Possible cause Countermeasures

Improve the fit, internal clearance, preload position of housing shoulder,

Abnormal load
etc.

Improve the machining accuracy and alignment of shaft and housing,

Incorrect mounting
accuracy of mounting method.
Loud metallic
sound1
Insufficient or improper lubricant Replenish the lubricant or select another lubricant.

Contact of rotating parts Modify the labyrinth seal, etc.

Dents generated by foreign matter, corrosion, flaws, or scratches on

Replace or clean the bearing, improve the seals and use clean lubricant.
raceways
Noise
Loud regular
Brinelling Replace the bearing and use care when handling bearings.
sound

Flaking on raceway Replace the bearing.

Excessive clearance Improve the fit, clearance and preload.

Irregular
Penetration of foreign particles Replace or clean the bearing, improve the seals and use clean lubricant.
sound

Flaws or flaking on balls Replace the bearing.

Excessive amount of lubricant Reduce amount of lubricant or select stiffer grease.

Insufficient or improper lubricant Replenish lubricant or select a better one.

Abnormal Improve the fit, internal clearance, preload or position of housing

Abnormal load
temperature rise shoulder.

Improve the machining accuracy and alignment of the shaft and housing,
Incorrect mounting
accuracy of mounting or mounting method.

Creep on fitted surface, excessive seal friction Correct the seals, replace the bearing or correct the fitting or mounting.

Brinelling Replace the bearing and use care when handling bearing.

Flaking Replace the bearing.

Vibration
(radial runout of shaft)
Correct the squareness between the shaft and housing shoulder or side
Incorrect mounting
of spacer.

Penetration of foreign particles Replace or clean the bearing, improve the seals.

Leakage or discolouration Reduce the amount of lubricant, select a stiffer grease. Replace the
Too much lubricant. Penetration by foreign matter or abrasion chips
of lubricant bearing or lubricant. Clean the housing and adjacent parts.

Note (1) Squeaking may arise from grease lubricated ball bearings or cylindrical roller bearings (medium to large size). This is especially true during winter when temperatures are low. In general, even
though squeaking will occur, the bearing temperature will not rise, leaving fatigue or grease life unaffected. Consequently, such a bearing can continue to be used. If you have concerns regarding
squeaking noise, please contact NSK.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 53

 Upgrading
Overview

54
The following section shows how a spindle performance can be upgraded by
changing from a conventional design to a special product designed specifically
for certain applications. This section also shows where improvements can
be made by using updated products such as sealed bearings instead of open
bearings.

The following products are included here:

› Robust Design › TYN Cages

Designed for low temperature generation or higher speeds. Especially suitable for grease applications and used in
Both angular contact and cylindrical roller bearings available. angular contact bearings.

› Improved Material › TB Cages

Steel, ceramic and special NSK SHX or EP material choices Used to increase speed performance in cylindrical roller
are available for applications resulting in longer fatigue life bearings.
under severe conditions.
› TAC Conversions
› Sealed Bearings Converting from 60º double direction thrust bearings to the
Opportunity to eliminate contamination before and during more easy to fit and lubricate BTR and BAR Series 40º and
operation resulting in longer grease life. Available for angular 30º contact angle enabling higher speeds.
contact spindle bearings and ball screw support bearings.

› Hybrid Bearings
Bearings with ceramic balls, resulting in lower temperature,
higher speed, higher accuracy, reduced wear, higher stiffness
and longer life.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 55

 Upgrading
Robust Design – Angular Control

The ‘Robust’ design is a high-speed / low temperature range of bearings allowing

higher performance for the same envelope size.

Benefits: Designations examples:

› Low Heat Generation S-Type All steel 70BNR10STSULP3
› High Seizure Resistance H-Type Steel rings/ceramic balls 70BNR10HTSULP3
› Better Temperature Stability X-Type Special SHX material rings/ceramic balls 70BNR10XTSULP3
› Stable in High-Speed Operations XE-Type Special design same material as above 70BNR10XETSULP3

Spinshot™ II XE Type
Suitable for silent operation due to red-
uced air-noise achieved through air-oil
lubrication design
› Material of Inner/Outer Rings: Heat
Resistant Steel “SHX”
› Ceramic Balls
› Cage selection based on speed requirements
- Outer Ring Guided Phenolic Cage:
up to 2.5 million dmn
- Outer Ring Guided PEEK Cage:
over 2.5 million dmn

ROBUST Series X Type

High performance bearings demonstrating
high wear and seizure resistance during
ultra high-speed operation
› Material of Inner/Outer Rings:
Heat Resistant Steel “SHX”
› Ceramic Balls
High Performance

› Outer Ring Guided Phenolic Cage

ROBUST Series H Type

High performance bearings that combine high-speed
operation with low heat generation
› Material of Inner/Outer Rings: Steel
› Ceramic Balls
› Cage selection based on speed requirements:
- Ball Guided Polyamide Cage: up to 1.4 million dmn
- Outer Ring Guided Phenolic Cage over 1.4 million dmn

ROBUST Series S Type

Steel ball bearings for optimal cost
› Material of Inner/Outer Rings: Steel
› Steel Balls
› Ball Guided Polyamide Cage

High-Speed

56
Upgrading
Robust Design – Cylindrical Roller Bearings

The complete range of NSK cylindrical roller bearings are designed to achieve high-speed
performance combined with high rigidity. At the top of this range is the ‘Robust’ series.

Benefits: Designations examples:

› Low Heat Generation Single row – Standard series N1014BMR1KRCC0P4
› Improved Seizure Resistance Single row – ‘Robust’ series, RS type N1014RSTPKRCC0P4
› Stable in Ultra-High-Speed Double row – High Rigidity series NN3014TBKRE44CC0P4
Single row – ‘Robust’ series, RX type N1014RXTPKRCC0P4
Single row – ‘Robust’ series, RXH type N1014RXHTPKRCC0P4

Ultra High-Speed Single Row

Cylindrical Roller Bearings
ROBUST Series RXH Type
High performance for optimum seizure resistance
during high-speed operation
› Material of Inner/Outer Rings: Heat Resistant Steel “SHX”
› Ceramic Rollers
› Outer Ring Guided PEEK Cage

Ultra High-Speed Single Row

Cylindrical Roller Bearings
ROBUST Series RX Type
High performance with wear and seizure resistance
during high-speed operation
› Material of Inner/Outer Rings: Heat Resistant Steel “SHX”
› SHX Rollers
› Outer Ring Guided PEEK Cage
High Performance

Double Row Cylindrical Roller Bearings

High Rigidity Series
High performance series with a newly developed polymer cage
› Material of Inner/Outer Rings: Steel
› Roller Guided PPS Cage or Roller Guided Brass Cage
(Selection based on application requirements)

Ultra High-Speed Single Row Cylindrical Roller

Bearings
ROBUST Series RS Type
Designed to deliver cost effective high-speed performance
› Material of Inner/Outer Rings: Steel
Single Row Cylindrical › Steel Rollers
Roller Bearings › Outer Ring Guided PEEK Cage
Standard Series
Standard type bearings with brass cage
› Material of Inner/Outer Rings: Steel
› Rollers Guided Brass Cage

High-Speed

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 57

 Upgrading
Bearing Material

Three types of steel materials support long life and high performance
of NSK Super – Precision bearings.

Z Steel EP Steel (Extremely Pure)

This is now the standard steel used for precision bearings. The number and size of particles within the steel affects
This steel is an improvement on the conventional carbon the fatigue life of the material particularly under high loads.
chrome bearing steel i.e. vacuum degassed steel (SAE52100, A new inspection process developed by NSK enabled the
SUJ2). It is specially produced by reducing the amount of development of this extremely pure (EP) steel for use in high
non-metallic inclusions, oxides and other inclusions such load applications.
as Ti (Titanium) and S (Sulphur). Tests have proved that Compared to Z steel it can be seen that the fatigue life is
this significantly improves the bearing fatigue life. superior. The graph also shows that the slope of the fatigue
results for the EP steel is almost vertical, this is an indication
of high reliability. All the Ball Screw Support (TAC) bearings are
Oxygen Content in Steel and Fatigue Life
Operating Life* Subsurface Originated Flake Test
made from this EP material.
EP steel results in a fatigue life increase of 3 times longer
Cycle
108
Z Steel 99
90
than conventional Vacuum degassed steel.
Cumulative Failure Probability (%)

Vacuum degassed steel 80 Test Conditions (Bearing: 6206)

for the bearings in a wide 70 P/C: 0.71
variety of industries 60
50 Speed: 3900min-1

107
40
30
20
Lubrictaion: Forced
Circulation Oil
SHX Steel
10
This is a special material designed by NSK for Ultra high-speed
Life (L10)

9
8
7
6
5 applications. It is a highly heat and wear resistant steel using
106 4
EP Steel
3
2
1
Z Steel special NSK heat treatment technology.
0 5 10 20 30
Oxygen Content in Steel (ppm) PPM = Part per milion
Life (h) At extreme speeds the wear resistance of the material is very
important, this is particularly true for cylindrical roller bearings.
Seizures can occur due to wear and high temperature.
Z steel results in a fatigue life increase of 1.8 times longer than conventional
The SHX material exhibits both wear and heat resistance
Vacuum degassed steel.
When calculating fatigue life of NSK precision bearings in Machine Tool similar or better than M50 (Aerospace steel used on main
applications which are relatively clean and not highly loaded, the fatigue life of Z shaft bearings up to 300°C).
steel can be increased by approximately 14 times.
The SHX material is used for part of the ‘Robust’ range for
both angular contact and cylindrical roller bearings. For the
Wear Resistance of each Material (2 cylindrical rollers wear test) cylindrical roller bearing it offers speeds almost as good as
0.07 ceramic roller bearings for a significantly lower price. This
0.06 SHX option is only available from NSK.
SUJ2
0.05 SHX steel results in a fatigue life increase of 4 times
Amount of Wear (g)

M50
0.04 longer than conventional Vacuum degassed steel at 20%
0.03 higher speed.
0.02
0.01
0
0 500 1000 1500 2000
Sliding Distance (m)

58
Upgrading
Sealed Bearings

Upgrading to sealed bearings is a major advantage to increasing life and performance of

spindle bearings. Sealed angular contact bearings are thesame external dimensions as open
bearings so interchange is easy.

Spindle in vertical operations

Benefits of Sealed Bearings
1. Time saving to end user, no grease fill operation –
Bearings pre-greased by NSK
NSK greased bearings are filled with high performance grease.
This saves the user time by eliminating the greasing process
and ensures that the correct quantity of grease is applied in t
he correct position in ultra clean conditions.

2. Reduced down time – Eliminate contamination through poor

handling
Sealed bearings prevent contamination entering the
bearing during handling and fitting to the spindle. Grease
in an unsealed bearing can attract dust and metallic debris.
Contamination in the bearing will cause the raceways to
wear and cause premature failure.

3. Better spindle performance –

Prevents grease migration in vertical spindles
Spindles in vertical operations can vary in temperature due to
grease falling out of the uppermost bearing into the path of
the lower bearing. Sealed bearings prevent this occurring and
because the seals are non-contacting type, the speed capability
is the same as open bearings.

4. Higher accuracy due to reduced contamination –

Bearing Type: 65BNR10HTDB (Open Type) 65BNR10HTV1VDB (Sealed Type) Prevents entry of contaminants in operation
The sealed bearing eliminates solid contamination entering the
Speed: 18,000 min-1
(dmn= 1.48 million)

Open
bearing during operation. This prevents noise and vibration in
Sealed continuing the bearing. Vibration can result in loss of accuracy of machined
components.
0 2000 4000 6000 8000 10,000 12,000 14,000 16,000
Life (Hours) Preload: 300N Stiffness: 100N/µm
5. Longer grease life – Seals prevent loss of grease and reduce
ageing
A sealed bearing not only prevents premature failures due to
contamination, but also extends the grease life by preventing grease
loss during operation. This results in at least a 50% increase in life.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 59

 Upgrading
Sealed Bearings

Standard Series Designations System

E.g. bearing number: 7010CTRV1VSULP3 MTSX Sealed bearings are available in two series: standard precision
and High-Speed ‘Robust’ Precision from 30mm to 100mm bore.
Ultra High-Speed Robust Series
‘V1V’ signifies a sealed bearing.
E.g. bearing number: 60BNR10XTV1VSUELP3MTSX

Summary of Benefits
› Grease in optimum quantity and position
Time saving for end user
› Clean handling
Eliminates downtime
› No grease migration in application
Improved performance
› Reduced external contamination in application
Higher accuracy
› Longer grease life
1.5 times the life of an open greased bearing

60
Upgrading
Sealed TAC

Sealed Ball Screw Support Bearings are now available with seals for extra
reliability in dusty and water/oil contaminated environments.

The seals are contacting type, which means that the sealing
High barrier contact properties are excellent and each seal is a different colour
seal on each side to help identify the front and rear face of the bearing. A vee
line is also marked on the outer ring surface for additional
indication (point of vee showing front face).The grease for
the sealed bearings is a special WPH waterproof type; this
Water proof grease provides an additional barrier against water contamination.

Although these seals are contacting for additional protection,

the low friction design prevents high temperature generation.
* Different coloured seal on each side to identify

Temperature Rise The left graph shows the advantages of this new design.
40
Bearing Size: Ø 30x Ø 62x Ø 15mm 3000rpm Normally some type of external seal would be required
35 Combination: DFD 2000rpm
to protect in wet conditions; it can be seen that the new
Outer ring Temperature

30 Preload: 4500N 1000rpm

25 sealed bearings run at a lower temperature than the same
Rise (°C)

20 open type using an external sealing arrangement.

15
10
5
0
Current Current New Type
(with External Seal) (without External Seal) (Sealed)

Coolant Contamination Ratio The left graph shows the effectiveness of the low friction
0.9 contact seals in the ability to prevent water ingress.
0.8
However the use of the seals also prevents dust and other
Water Contamination Ratio

Bearing Size: é 30x é 62x é 15mm

0.7 Combination: DFD
contamination from entering the bearing during the fitting
in Grease (wt%)

0.6 Speed:1200min-1
Preload:4500N
0.5
Operating Time: 60hr process and prevents the loss of grease from the bearings
0.4
0.3
particularly in vertical ball screw applications. Reducing
0.2 the grease leakage improves the life of the bearing
0.1
considerably.
0
Current New Type
(External Seal) (Sealed)

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 61

 Upgrading
Sealed TAC

Grease Leakage This new product is standardised for Single Universal (SU)
30 arrangements and is available from 15mm to 45mm bore size.
Brg: 30TAC62B
25
Leakage Amount (%)

Speed: 3000min-1

20

15 Designation Example:
90% 30TAC62BDDGSUC10PN7B (DDG = seal symbol)
10
Reduced
5

0
Open with Seal

Summary of Benefits
› Longer life
› Reduced grease loss
› Low temperature compared to conventional
sealing arrangements
› Prevent water and dust ingress
› Better handling

62
Upgrading
Hybrid Bearings

Many machine repairers are upgrading to hybrid - (steel ringed bearings using
silicon nitride ceramic balls) in order to improve reliability, particularly in situations
where warranties are extending from 1 to 2 and sometimes up to 3 years.

Features of Hybrid Bearings – Lighter Weight

Due to mass being approximately 40% of steel, hybrid
bearings can run up to 25% faster than conventional
all steel bearings. This also means that the generated
temperature is also lower.

Smoother Surface
The surface finish of the ceramic ball is much smoother than
the steel ball, this improves the accuracy of rotation and the
part being manufactured.

Harder and Stiffer

Lighter
The ceramic ball is much harder than a conventional steel ball
Weight
(HV 1700@ <800°C compared to HV 700@20°C). This means
Smoother Harder & that the ceramic ball is less likely to be damaged by small
Surface Stiffer
amounts of hard contamination. Higher stiffness means that
the hybrid bearing will distort less under high load compared
to the steel ball type.
Lower Corrosion &
Thermal Electrical
Expansion Resistance Corrosion and Electrical Resistance
These bearings can be run in more arduous environments.
The electrical resistance prevents pitting of the ball surface
due to electrical discharge in built-in motor spindles.

Designation System:
Grease Lubricated
7014CSN24TRSULP3 (Standard Precision Product)

Temperature Rise (ºC) 70BNR10HTSULP3 (High-speed ‘Robust’ Product)

20 Bearing: 7006C
Speed: 34000 min-1
15 (1.455Mdmn)
Preload:
Summary of Benefits
10 Conventional 318N - Constant Type › Higher Speed › Longer Life
Bearing (spring)
5
Hybrid › Cooler Temperature › Higher Accuracy
Bearing
› Higher Reliability
0
7006C Bearing Speed: 34000 rpm Preload: 318N

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 63

 Upgrading
TYN Cages

TYN Cage The majority of angular contact bearings use phenolic type
cages and these are exceptional good for a wide range of
conditions and particularly for high-speed since they are outer
ring located. However, there are advantages to using TYN
cages in certain applications, particularly in grease lubrication.
TYN is a polyamide material and this cage is designed to be
ball guided.

Reduced Cage Noise

In certain applications cage noise can occur in grease
lubricated bearings. This is due to friction between the
Low Noise ballsurface and the cage guide surface; this can be
particularly noticed in cold conditions. The TYN cage
design eliminates this due to the very low friction quality
of the material and good vibration absorption characteristics
Self-Excited Vibration as well as improvements in the cage shape.

The test data left shows the comparison of the Phenolic

Temperature
Cage Grease and Polyamide cage:
Room 0ºC -10ºC
(20ºC)
Multemp PS2 A A A
Longer Grease Life – Shorter ‘Running In’ Time
TYN Isoflex NBU15 A A A
Grease life is longer because there is more internal space for
Isoflex NBU8EP A A A
Multemp PS2 B C
the grease to collect in and because the grease can clear the
Phenolic Isoflex NBU15 B C rotating parts more quickly, the running in time is reduced.
Isoflex NBU8EP C

A: No cage noise, B: cage noise often observed, C: cage noise was observed. Cage Guiding Contact:
TYN cage runs silence compared to phenolic cage
More grease space with TYN. Less grease pushed out of
bearing, therefore, longer life. Shorter running in time
Larger Grease Reservoir Position of Guiding compared to Phenolic and more stable temperature
characteristics.

Higher Strength
Ball Guided Outer Ring
Polyamide (TYN) Guided Phenolic The TYN material has both higher bending and tensile
(T/TR) strength. TYN cages can be used up to a speed of 1.4Mdmn.
(Mean bearing diameter in mm X speed in rpm.)
This covers most grease lubricated applications.
Above 1.4Mdmn phenolic cage should be selected.
Cage Type Bending Strength MPa Tensile Strength MPa
T/TR 150 90 Examples of Designation:
TYN 237 172
7014CTYNDULP3 (Standard Precision)
Strength measured on test piece, not complete cage
70BNR10TYNDULP3 (High-Speed Precision)

64
Upgrading
TAC Conversions

Traditionally, medium to large lathes require very good

radial and axial rigidity. For this reason it is normal to use
a configuration of roller bearings and thrust bearings at the
front of the spindle for radial and axial rigidity respectively.
The conventional type thrust bearing was a double row,
bi-directional 60° contact angle TAC series bearing. This is still
available for bore sizes of 140mm and above. However for
lathe spindles below this size the requirements are now for
higher speed and/or lower temperature performance. For this
reason a new type of thrust bearing has been designed to fit
25 this requirement.
Outer Ring Temp. Rise (ºC)

20

15
New ‘Robust’ Design BAR and BTR Thrust Bearings
This new range has the same size and number of balls as
10
100TAC20X (α0=60º) the TAC series but have special internal geometry and lower
100BTR10STYNDB (α0=40º)
5 100BAR10STYNDB (α0=30º)
Grease lubrication (Isoflex NBU15)
contact angles (30° or 40°) enabling low heat generation,
-1
0 Speed (min )
higher speed performance and good axial rigidity.
0 1000 2000 3000 4000 5000 6000 7000
4
(x10 dmn)
0 10 20 30 40 50 60 70 80
Higher Speed Performance
The new thrust bearing design can run to higher speeds,
BAR (30°) being the fastest followed by BTR (40°) which
Relative Speed Interchangeability has a higher rigidity compared to BAR but still runs faster
200
B
A
C than the original TAC (60°).
A = 2B
D The new thrust bearings can
also be supplied in hybrid types (ceramic balls) enabling
180
160
Relative Speed

140
120
100 even higher speeds and rigidities.
80
B B
60
40
20
0
TAC BTR BAR Interchangeability
Steel Ceramic The width of the pair of new thrust bearings is special to allow
High speed with Robust design
New
B product also with ceramic balls
A
C A = 2B
D easy interchange between the old TAC type bearing. The outer
diameter tolerance is the same as the TAC bearings to enable
a clearance fit in the housing, this ensures radial load is only
Low Heat Generation
B B
taken by the adjacent roller bearing.
› ROBUST design enables
low heat generation and Example of designation:
Advantages
high-speed operation. › Reduced components – Original 60° type: 100TAC20DPN7+LC6
eliminates outer spacer B
› Longer grease life thanks New 30° type: 100BAR10STYNDBLP4A (S=steel, H=Hybrid)
› Easy mounting since single
to reduced grease row bearing structure New 40° type: 100BTR10STYNDBLP4A (S=steel, H=Hybrid)
› Easy to upgrade from old to
deterioration and TYN new design – only inner ring
spacer
resin cage. needs to change
› Better machining accuracy. › (C to D), bore and OD same as
old design

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 65

 Upgrading
TB Cages

An exciting new material has been patented by NSK for use in roller bearings.
This new material is an engineered polymer called ‘PPS’ Polyphenylene sulphide
and is designated TB type.

Longer Life
Experiments also showed that the TB cage could be run
under higher preloaded conditions and closer to boundary
lubrication compared with brass cages. In endurance tests
under severe conditions wear could be found in the Brass
cage bearings after 200 hours compared to 300 hours for the
PPS material of the TB cage.

Example of Designation:
NN3022TBKRE44CC0P4

Speed
Advantages over
Brass MB type cage
NN3022 Grease
› Reduced wear
› Higher speed
› Lower temperature Brass 5400 rpm Typically
(MB) 11-14%
› Longer life
increase in
speed with
PPS (TB) 6100 rpm
TB cages

Speed
MB Brass Cage TB PPS Cage

66
 Wear Resistance Lower Temperature
Grease discolouration due to wear on brass cage
MB cage before testing MB cage after testing 4
dmNx10
0 24 48 72 96 120 144 168
30
MB TB
25 MB
Outer Ring Temp. Rise oC

20
TB
15
Reduced wear using TB cage
10
TB cage before testing TB cage after testing Grease Lubrication
Target Clearance : 0µm
5 Orientation : Horizontal

0
0 2000 4000 6000 8000 10000 12000 14000
-1
Shaft Speed (min )

Size and Range

Bearing Type Cage Symbol Specification Available Size

NN3920 to NN3956
MB Roller guided machined brass cage NN3920 to NN3956
NN
NN4920 to NN4940
TB Roller guided PPS resin cage NN3006 to NN3024

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 67

 Supplementary Information
Bearing Interchange Guide

Interchange Guide for Precision Angular Contact Bearings

(Symbols in brackets show seal designation when available; Items in red are the manufacturers identifiers of particular parameters)

Example of 25 degrees contact angle

Standard ISO
NSK SKF SNFA Fafnir FAG
Design Series

19 79xxA5(V1V) 719xxACD SEBxxxxx3 3xx93xxWI B719xxE.(2RSD)

10 70xxA5(V1V) 70xxACD SEBxxxxx3 3xx91xxWI B70xxE.(2RSD)

02 72xxA5 72xxACD E2xxxxx3 3xx21xxWI B72xxE.(2RSD)

19 79xxA5SN24(V1V) 719xxACD/HC SEBxx/NSxxx3 3xxC93xxWI HCB719xxE.(2RSD)

10 70xxA5SN24(V1V) 70xxACD/HC EXxx/NSxxx3 3xxC91xxWI HCB70xxE.(2RSD)

High-Speed ISO
NSK SKF SNFA Fafnir FAG
Design Series

19 xxBER19 (V1V)S 719xxACE VEBxxxxx3 3xx93HX(VV) HS(S)719xxE

10 xxBER10 (V1V)S 70xxACE VEXxx(/S)xxx3 3xx91HX(VV) HS(S)70xxE

19 xxBER19 (V1V)H 719xxACE/HC VEBxx(/NS)xxx3 3xxC93HX(VV) HC(S)719xxE

10 xxBER10 (V1V)H 70xxACE/HC VEXxx(/S)/NSxxx3 3xxC91HX(VV) HC(S)70xxE

19 xxBER19 (V1V)X – VEBxxXNxxx3 – XC(S)719xxE

10 xxBER10 (V1V)X – VEXxx(/S)/XNxxx3 – XC(S)70xxE

Special material rings/

Steel balls Ceramic balls Steel balls sealed Ceramic balls sealed
Ceramic balls (Sealed)

Interchange Guide for Ball Screw Support Bearings

Series NSK INA SKF TIMKEN

No flange single BSNxxxxDDUHP2B ZLKNxxxx-(2Z/2RS) BEAM0xxxx-(2RZ/2RS) MMN5xxBSxxPP DM

No flange single BSFxxxxDDUHP2B ZLKFxxxx-(2Z/2RS) BEAS0xxxx-(2RZ/2RS) MMF5xxBSxxPP DM

No flange pair BSNxxxxDDUHP2BDT ZLKNxxxx-(2Z/2RS)-2AP - MMN5xxBSxxPP QM

No flange pair BSFxxxxDDUHP2BDT ZLKFxxxx-(2Z/2RS)-2AP - MMF5xxBSxxPP QM

Interchange Guide for Precision Thrust Bearings

Thrust Bearings for Spindle Applications
NSK SKF SNFA Fafnir FAG
Contact Angle

30 degrees xxBAR BTMxx A/DB – – –

40 degrees xxBTR BTMxx B/DB – – –

60 degrees xxTAC 2344xx – – 2344xx

Interchange Guide for Precision Ball Screw Support Bearings

Series NSK SKF SNFA Fafnir FAG

Non-ISO Metric (30 bore, 62 OD, 15 w) 30TAC62B BSD3062C BS3062 MM30BS62 BSB030062
ISO Metric (30 bore, 62 OD, 16 w) BSB2030 BSA206C BS230 - 760230

INCH (23.838 bore, 62 OD, 15.875 w) BSB093 BDAB634201C – MM9308WI2H –

68
Interchange Guide for Precision Cylindrical Roller Bearings

Standard Design Construction NSK SKF FAG

NN39xx(KR) – –

NN30xx(KR) NN30xx(K) NN30xx(K)

NN49xx(KR) – –

NNU49xx(KR) NNU49xx(K) NNU49xx(K)

N10xx(KR) N10xx(K) N10xx(K)

High Speed Design Construction

High Speed Design Construction (*) NSK SKF FAG

Steel Rollers
NN10xxRS(KR) – –
and Rings

Ceramic Rollers and

N10xxRXH(KR) N10xxHC5(K)(*) HCN10xx(K)
Special Steel Rings

Special Steel Rollers

N10xxRX(KR)
and Rings

(*) Normal steel rings used only

This interchange should be used as a guideline only, as manufacturers’ designations may change without notice.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 69

 Supplementary Information
Bearing Failures and Countermeasures

This next section will explain the most common forms of bearing failure in a
machine tool application with possible causes and countermeasures. This section
includes a diagnostic chart to help the end user to quickly focus on the most
important reasons for the failure.

Inspection of the dismantled bearings often reveals that the Bearing Failure and Countermeasures
most common cause of bearing failure is contamination of In general, if rolling bearings are used correctly they
either hard particles or liquid. This often causes noise and will survive to their predicted fatigue life.
vibration and can be detected by the methods outlined at However, they often fail prematurely due to avoidable
the end of this section. mistakes. In contrast to fatigue life, this premature failure
is caused by improper mounting, handling or lubrication,
Maintenance, Inspection and Correcting Irregularities entry of foreign matter, or abnormal heat generation. For
In order to maintain the original performance of a bearing instance, the causes of rib scoring, as one example, are the
for as long as possible, proper maintenance and inspection use of improper lubricant, faulty lubricant system, entry of
should be performed. If correct procedures are used, foreign matter, bearing mounting error, excessive deflection
many bearing problems can be avoided and the reliability, of the shaft or any combination of these. Thus, it is difficult
productivity, and operating costs of the equipment containing to determine the real cause of some premature failures.
the bearings are all improved. It is suggested that periodic
maintenance be done following the procedure specified. If all the conditions at the time of failure and previous to
This periodic maintenance encompasses the supervision of the time of failure are known, including the application, the
operating conditions, the supply or replacement of lubricants, operating conditions, and environment; then by studying the
and regular periodic inspection. Items that should be regularly nature of the failure and its probable causes, the probability
checked during operation include bearing noise, vibration, of similar future failures can be reduced. The most frequent
temperature, and lubrication. types of bearing failure, along with their causes and
corrective actions, are listed in the table.
If an irregularity is found during operation, the cause should
be determined and the proper corrective actions should be
taken after referring to the table.
If necessary, the bearing should be dismounted and
examined in detail.

70
The types of problems reported by end users
fall into the following categories:

Reason For Return/Bearing Problem

Axial Clearance/
Preload Problem
10%
Notchy to Turn
5%

Excessive Heat
10%

Noise Vibration
60%
Failure/Collapse
15%

Causes of Bearing Problem

Out of Balance 4%

Lubrication
8%

Radial Preload/
Incorrect Fits
17%

Contamination
63%

Fitting
Error
4%

Abnormal
Load
4%

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 71

 Supplementary Information
Bearing Failures and Countermeasures

Causes and Countermeasures for Bearing Failures

Type of Failure Irregularities Photo Probable cuases Countermeasures

When mounting the outer ring of free-

Flaking on one side of the Abnorma axial load (sliding failure of
side bearings, it should be fitted loosely,
raceway of radial bearing. free-side bearing)
to allow axial expansion of the shaft.

Flaking pattern inclined relative to Use care in mounting and centering,

Improper mounting, bending of shaft,
the raceway in radial ball bearings. select a bearing with a large clearance
inadequate centering, inadequate
Flaking near the edge of the raceway and correct the squareness of shaft and
tolerances for shaft and housing.
and rolling surface in roller bearing. housing shoulder.

Large shock load during mounting,

rusting while bearing is out of Use care in mounting and apply a rust
Flaking of raceway with same
Flaking operation for prolonged period, preventative when machine operation
spacing as rolling element.
mounting flaws of cylindrical is suspended for a long time.
roller bearings

Premature flaking of raceway Insufficient clearance, excessive load, Select proper fit, bearing clearance and
and rolling element. improper lubrication, rust, etc. lubricant.

Premature flaking of combined bearings. Excessive preload. Adjust the preload.

Inadequate initial lubrification,

Scoring or smearing between raceway Use a softer grease and avoid rapid
excessively hard grease, high
and rolling surface. acceleration.
acceleration when starting operation.

Scoring

Scoring or smearing between the end Inadequate lubrication, incorrect Select proper lubricant and modify
face of the rollers and guide rib. mounting and large axial load. the mounting.

Excessive shock load, excessive Examine the loading conditions, modify

interference in fitting, poor shaft the fit of bearing and sleeve, improve
Crack in outer or inner ring. cylindricity, improper sleeve taper, large accuracy in machining shaft and sleeve,
fillet radius, development of thermal correct fillet radius (the fillet radius must
cracks and increased flaking. be smaller than the bearing chamfer).

Increased flaking, shock applied to rib

Use care in mounting and
Cracks Crack in rolling element or broken rib. during mounting or dropped during
handling a bearing.
handling.

Abnormal loading on the cage

Correct mounting and examine the
Fracture of cage. due to incorrect mounting.
lubrication method and lubricant.
Improper lubrication.

72
Type of Failure Irregularities Photo Probable cuases Countermeasures

Indentation on raceway with the same Shock load during mounting or

Use care in handling the bearing.
spacing as rolling element (brinelling). excessive load when not rotating.

Indentations

Indentation on raceway and Entry of foreign matter such as Clean the housing, improve the seals
rolling elements. metallic particles and grit. and use clean lubricant.

Vibration of the bearing without rotation Secure the shaft and housing use oil
False brinelling
when out of operation, such as during as a lubricant and reduce vibration by
(phenomenon similar to brinelling).
transport or rocking motion of vibration. applying preload.

Fretting, localized wear with reddish- Sliding wear at a minute gap in the
Increase interference and apply oil.
brown wear dust at fitting surface. fitting surface.

Abnormal
wear

Wearing on raceway, rolling elements, rib Entry of foreign matter, incorrect Improve sealing capabilities, clean the
and cage. lubrication and rust. housing and use a clean lubricant.

Insufficient interference, insufficiently Modify the fitting and tighten

Creep, scoring wear at fitting surface.
secured sleeve. the sleeve properly.

Examine the fitting and internal

clearance of a bearing, supply an
Discoloration and melting of raceway, Insufficient clearance, incorrect
Seizure adequate amount of proper lubricant
rolling elements and ribs. lubrifacation, or improper mounting.
and examine the mounting method
and quality of related parts.

Store carefully when in a moist or hot

Condensation of water from the air, or climate, take rust prevention measures
Corrosion Corrosion and rust at bearing interior or
fretting, entry of corrosive substance before removing from operations for a
and Rust fitting surface.
(especially varnish gas). long time, and select proper varnish
and grease.

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 73

 Supplementary Information
Bearing Failures and Countermeasures

Typical causes

Bearing Lubrica-
Handling Load Speed
surrounding tion

Bearing selection
Oscillating, vibration,
Damage name Location (phenomenon) Remarks

Lubricant method

High speed, high

Stock, shipping

Sealing device,

Too small load

Shaft, housing

Excessive load

Moment load
water, debris

Temperature

acceleration

stationary
Lubricant
Mouting
01. Flaking Raceway, rolling surface

Raceway, rolling contact surface

02. Peeling
Bearings outer diameter surfaces * mating rolling part

Roller end surface, rib surface

03. Scoring
Cage guide surface, pocket surface

04. Smearing Raceway, rolling surface

05. Fracture Raceway collar, rollers

Raceway rings, rolling elements

06. Cracks
Rib surface, roller end face, cage guide surface
(thermal crack)

(Deformation), (fracture)
07. Cage damage
(Wear)

Raceway, rolling surface,(innumerable small dents)

08. Denting
Raceway (debris on the rolling element pitch)

09. Pitting Raceway, rolling surface

10. Wear Raceway, rolling surface, rib surface, roller end face

Raceway, rolling surface

11. Fretting
Bearing outside and bore, side surface
(Contact with housing and shaft)

12. False brinelling Raceway, rolling surface

* *
13. Creep Raceway, rolling surface * Loose fit

14. Seizure Fitting surface

* * * Electricity passing
15. Electrical corrosion Raceway, rolling surface through the rolling
element

16. Rust and corrosion Raceway ring, rolling element, cage

17. Mounting flaws Raceway, rolling surface

18. Discoloration Raceway ring, rolling element, cage

Remark: This table is not comprehensive. It lists only the more commonly occurring damages, causes, and locations.

74
Supplementary Information
Trouble Shooting

Sound and Vibration -

Classification of Sounds and Vibrations By recording sounds and vibrations of a rotating machine and
Sound and vibration accompany the rotation of rolling bearings. analysing them, it is possible to infer the cause. As can be
The tone and amplitude of such sound and vibration varies seen from the charts below, a mechanically normal bearing
depending on the type of bearing, mounting conditions, shows a stable waveform. However, a bearing with a scratch,
operational conditions, etc. The sound and vibration of a for example, shows a waveform with wide swings indicating
rolling bearing can be classified under the following four chief large-amplitude sounds at regular intervals. NSK produces a
categories listed in the table on page 76 and each category can Bearing Monitor NB-4, a vibration measuring monitor that can
be further classified into several sub-categories, as described in diagnose irregularities in a rotating machine. The causes of
the table overleaf. Boundaries between groups are, however, the irregularities can be inferred using the NB-4 and recording
not definite. Even if some types of sounds or vibrations are equipment, such as a personal computer.
inherent in the bearings, the volume might be related to
the manufacturing process, while some types of sounds or
vibrations, even if they arise due to manufacturing, cannot
be eliminated even in normal conditions.

Vibration Measuring Equipment, Bearing Monitor NB-4

Sound waveform of a normal bearing

Sound waveform of a scratched bearing

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 75

 Supplementary Information
Trouble Shooting

Classification of Sounds and Vibrations in a Rolling Bearing

Sound Vibration Features

Continuous noise, basic unavoidable noise which all bearings

Race noise Free vibration of raceway ring
generate

Free vibration of raceway ring, Regular noise at a certain interval, large bearings and
Click noise
free vibration of cage horizontal shaft, radial load and low rpm

Intermittent or continuous, mostly large cylindrical roller

Squeal noise Free vibration of raceway ring
bearings, radial load, grease lubrication, at particular speed

Regular noise at a certain interval,

Structural “CK” noise Free vibration of cage
all bearing types generate it

Cage noise “CG” noise Vibration of cage Intermittent or continuous, lubrication with particular grease

Certain interval, but a little irregular

Tapping noise Free vibration of cage
under radial load and during initial stage

Continuous,
– Rolling element passage vibration
all bearing types under radial load

Inner ring Continuous noise

Vibration due to
Manufacturing Waviness noise Outer ring Continuous noise
waviness

Rolling element Continuous with rollers, occasional with balls

Inner ring

Vibration due to
Flaw noise Outer ring Regular noise at a certain interval
flaw
Handling
Rolling element

Vibration due to
Contamination noise Irregular
contamination

Seal noise Free vibration of a seal Contact seal

Lubricant noise – Irregular

Others fr Continuous

– Runout fc Continuous

fr – 2fc Continuous

n: Positive integer (1, 2, 3...)

Z: Number of rolling elements
f RiN: Ring natural frequency in radial bending mode, Hz
f MI: Natural frequency in the mode of angular vibration in inertia of outer ring-spring system, Hz
f r: Rotation frequency of inner ring, Hz

76
 Generated frequency (frequency analysis)

FFT of original wave FFT after Source Countermeasures

envelope
Radial (angular) direction Axial direction (basic No.)
Selective resonance of waviness Improve rigidity around the bearings, appropriate radial
f RiN , f MI f AiN , f AM -
(rolling friction) clearance, high-viscosity lubricant, high-quality bearings
f RiN , f MI f AiN , f AM Collision of rolling elements with inner
Zf c Reduce radial clearance, apply preload, high-viscosity oil
Natural frequency of cage ring or cage
Self-induced vibration caused by Reduce radial clearance, apply preload, change thegrease,
( ≈ f r2N , f r3N) - -
sliding friction at rolling surface replace with countermeasured bearings
Collision of cage with rolling elements
Natural frequency of cage fc Apply preload, high-viscosity lubricant, reduce mounting error
or rings
Self-induced vibration caused by
Natural frequency of cage - Change of grease brand, replace with countermeasured cage
friction at cage guide surface
Collision of cage and rolling element Reduce radial clearance, apply preload, low-viscosity
Natural frequency of cage Zf c
caused by grease resistance lubricant
Displacement of inner ring due to
Zf c - - Reduce radial clearance, apply preload
rolling element passage
Inner ring raceway waviness, irregula-
nZf i ± f r (nZ ± 1 peaks) nZf i (nZ peaks) - High-quality bearings, improve shaft accuracy
rity of shaft exterior
Outer ring raceway waviness, irregular
nZf c (nZ ± 1 peaks) nZf c (nZ peaks) - High-quality bearings, improve housing bore accuracy
bore of housing

2nf b ± fc (2n peaks) 2nf b (2n peaks) - Rolling element waviness High-quality bearings

Nicks, dents, rust, flaking on inner ring

Zf i Replacement and careful bearing handling
raceway
Nicks, dents, rust, flaking on inner ring
f RiN , f MI f AiN , f AM Zf c Replacement and careful bearing handling
raceway
Nicks, dents, rust, flaking on rolling
2f b Replacement and careful bearing handling
elements

f RiN , f MI f AiN , f AM Irregular Entry of dirt and debris Washing, improve sealing

Self-induced vibration due to friction at

Natural frequency of seal ( f r) Change the seal, change the grease
seal contact area
Lubricant or lubricant bubbles crushed
- - Irregular Change the grease
between rolling elements and raceways

fr - - Irregular inner ring cross-section High-quality bearings

Ball variation in bearing, rolling

fc - - High-quality bearings
elements non-equidistant
Non-linear vibration due to rigid
f r – 2f c - - High-quality bearings
variation by ball variation

f c: Orbital revolution frequency of rolling elements, Hz

f AiN: Ring natural frequency in axial bending mode, Hz
f AM: Natural frequency in the mode of axial vibration in mass of outer ring-spring system, Hz
f i: f i = f r - f c Hz
f b: Rotation frequency of rolling element around its centre, Hz

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 77

 Supplementary Information
Bearing Preload Conversion Tables –
Standard Angular Contact

Preload Conversion Tables

Rule
In cases of emergency it is possible to change the preload
of a set of bearings, providing a spacer is used between the
opposing preloading bearings.
The tables on pages 79 – 83 show the amount of spacer
length adjustment required to change from one preload to
another.

For example, if the preload of a 7914 15º contact bearing

Spacers
needed to be changed from extra light to light, the inner
ring spacer length would need to be reduced by 6µm. From
To increase preload: reduce inner ring spacer medium to heavy would be 13µm reduction of inner ring
245.434
To reduce preload: reduce outer ring spacer
spacer length. If it was required to change from light to
heavy, it would be necessary to accumulate the values i.e.
12 and 13 to equal 25µm inner ring spacer length reduction.

In example when reducing the preload, select the same

values from the table below but reduce the length of the
outer spacer.

78
Standard Series
Series 79

15º contact angle 25º contact angle

preload preload
Extra light Light to Medium to Extra light Light to Medium to
Bearing number to light to medium to heavy to light to medium to heavy
µm µm µm µm µm µm

7900 3 3 5 1 4 3

7901 2 5 5 2 2 4

7902 3 4 7 2 3 5

7903 3 5 7 2 3 4

7904 4 5 7 3 3 6

7905 3 7 8 2 4 5

7906 3 6 7 2 3 5

7907 4 7 9 3 5 7

7908 4 9 10 2 6 7

7909 5 7 9 3 6 7

7910 4 10 10 3 6 8

7911 5 9 11 3 6 7

7912 4 9 11 3 5 8

7913 5 9 11 3 6 7

7914 6 12 13 4 7 10

7915 6 11 14 4 8 9

7916 5 12 13 4 7 10

7917 7 12 16 4 8 12

7918 6 14 16 4 8 11

7919 6 15 16 5 9 11

7920 8 14 19 5 9 12

7921 8 14 18 5 10 13

7922 8 14 18 5 10 13

7924 9 18 21 6 11 15

7926 10 18 23 7 11 16

7928 9 18 23 6 13 16

7930 11 20 25 7 14 19

7932 11 20 25 7 15 18

7934 11 20 25 7 14 19

7936 13 23 30 9 16 22

7938 13 24 30 9 16 22

7940 15 27 34 10 19 25

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 79

 Supplementary Information
Bearing Preload Conversion Tables –
Standard Angular Contact

Standard Series
Series 70

15º contact angle 25º contact angle 30º contact angle

preload preload preload
Extra light Light Medium Extra light Light Medium Extra light Light Medium
Bearing number to light to medium to heavy to light to medium to heavy to light to medium to heavy
µm µm µm µm µm µm µm µm µm

7000 3 5 7 3 3 5 5 5 5

7001 3 6 8 3 4 6 5 5 5

7002 4 6 9 2 5 5 5 5 5

7003 3 6 9 2 5 6 5 5 5

7004 4 8 10 3 6 7 5 5 5

7005 4 9 10 3 4 7 5 5 5

7006 4 10 11 3 6 8 5 5 5

7007 6 9 12 4 7 9 5 5 5

7008 5 11 13 4 6 9 5 5 5

7009 5 11 14 4 7 9 5 5 10

7010 6 12 14 4 7 10 5 5 10

7011 7 13 16 5 9 11 5 10 5

7012 7 15 16 5 8 11 5 10 5

7013 7 11 15 4 9 11 5 10 5

7014 7 16 18 5 9 13 5 11 9

7015 7 17 18 5 10 13 5 10 10

7016 8 17 21 5 12 14 10 10 10

7017 8 18 20 5 11 14 10 10 10

7018 10 19 23 6 12 16 10 15 10

7019 10 17 22 6 12 17 10 15 10

7020 9 19 23 6 13 16 10 15 10

7021 10 21 25 7 13 18 10 15 10

7022 12 24 29 8 15 20 15 15 15

7024 12 24 29 8 15 21 15 15 15

7026 13 25 31 8 16 22 15 20 15

7028 13 23 30 9 17 21 15 20 15

7030 14 25 32 9 17 24 15 22 23

7032 15 28 33 10 18 25 15 20 22

7034 17 31 38 11 22 28 20 17 23

7036 18 32 40 12 22 30 24 16 24

7038 19 34 43 12 24 32 25 18 26

7040 20 36 45 13 25 34 30 30 35

80
Standard Series
Series 72

15º contact angle 25º contact angle 30º contact angle

preload preload preload
Extra light Light Medium Extra light Light Medium Extra light Light Medium
Bearing number to light to medium to heavy to light to medium to heavy to light to medium to heavy
µm µm µm µm µm µm µm µm µm

7200 4 7 10 3 5 6 5 5 -

7201 4 9 10 2 6 7 5 5 5

7202 4 8 10 3 7 8 5 5 5

7203 4 12 12 3 7 7 10 5 5

7204 5 13 13 3 8 10 10 5 5

7205 5 11 11 3 7 10 10 5 5

7206 7 12 15 4 8 10 10 5 5

7207 7 15 18 4 10 12 10 5 10

7208 8 16 18 5 11 13 10 5 11

7209 9 14 19 5 12 15 10 10 10

7210 8 16 19 5 12 14 10 10 10

7211 9 21 22 6 13 16 10 16 9

7212 11 20 25 7 14 18 10 15 10

7213 11 21 26 6 15 18 10 15 10

7214 11 23 26 7 15 19 15 15 10

7215 11 21 26 7 15 19 15 15 10

7216 12 23 29 8 16 21 15 15 10

7217 13 26 32 9 16 22 16 19 15

7218 14 28 33 9 18 25 20 20 10

7219 15 30 36 10 19 26 15 20 15

7220 16 32 39 11 20 28 15 25 15

7221 17 35 41 12 21 29 20 20 20

7222 19 35 43 13 22 31 20 25 20

7224 19 35 43 13 24 33 20 30 15

7226 19 34 43 13 24 31 25 30 15

7228 21 37 49 14 26 35 31 29 15

7230 23 41 53 15 28 40 30 31 15

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 81

 Supplementary Information
Bearing Preload Conversion Tables –
Robust Series

Robust Series

BNR19S BER19S BNR19H,X,XE BER19H,X,XE

18º contact angle 25º contact angle 18º contact angle 25º contact angle
preload preload preload preload
Extra light Light Extra light Light Extra light Light Extra light Light
Bore size to light to medium to light to medium Bore size to light to medium to light to medium
µm µm µm µm µm µm µm µm

25 8 8 8 6 25 8 7 8 6

30 8 7 8 6 30 8 7 8 6

35 8 9 8 7 35 8 8 8 7

40 8 8 8 7 40 8 9 8 7

45 8 8 8 7 45 8 8 8 7

50 8 8 8 7 50 8 8 8 7

55 8 8 8 7 55 8 7 8 7

60 8 8 8 7 60 8 8 8 6

65 8 8 8 7 65 8 8 8 6

70 8 8 8 7 70 8 8 8 7

75 8 11 8 7 75 8 11 8 7

80 8 11 8 7 80 8 11 8 7

85 8 16 8 11 85 8 16 8 11

90 8 13 8 9 90 8 13 8 9

95 8 14 8 9 95 8 14 8 9

100 10 16 10 10 100 10 16 10 10

105 10 16 10 10 105 10 16 10 10

110 12 14 10 10 110 12 14 10 10

120 12 21 12 14 120 12 21 12 14

130 20 15 16 11 130 20 15 16 11

140 20 16 16 11 140 20 16 16 11

150 20 18 17 13 150 20 18 17 13

82
Robust Series

BNR10S BNR10S BNR10H,X,XE BER10H,X,XE

18º contact angle 25º contact angle 18º contact angle 25º contact angle
preload preload preload preload
Extra light Light Extra light Light Extra light Light Extra light Light
Bore size to light to medium to light to medium Bore size to light to medium to light to medium
µm µm µm µm µm µm µm µm

30 5 8 8 7 30 5 6 8 7

35 5 7 8 7 35 5 7 8 7

40 5 6 8 7 40 5 6 8 7

45 5 6 8 7 45 5 6 8 6

50 5 7 8 7 50 5 7 8 6

55 5 8 10 8 55 5 8 10 8

60 5 10 10 8 60 5 10 10 8

65 5 10 10 8 65 5 10 10 7

70 10 10 10 8 70 10 10 10 7

75 10 10 12 9 75 10 10 12 9

80 10 9 12 10 80 10 9 12 9

85 10 9 12 10 85 10 9 12 9

90 10 14 12 10 90 10 14 12 9

95 10 14 12 10 95 10 14 12 9

100 10 14 12 10 100 10 14 12 9

105 12 15 15 11 105 12 16 15 11

110 15 14 15 11 110 15 14 15 11

120 15 14 15 11 120 15 14 15 11

130 20 16 16 11 130 20 16 16 11

140 15 15 13 10 140 15 15 13 10

150 18 17 15 13 150 18 17 15 13

150 20 18 17 13 150 20 18 17 13

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 83

 Supplementary Information
Bore and OD Matching Chart

When selecting SU bearings or mixing sets of bearings to

Ring size deviations are shown on both the bearing rings and
box label as below. form a new or different arrangement, it is important to
ensure that the bore and OD deviations are within a certain
value. If the NSK sliding chart is not available, the tables
-3 -1
shown can be used to select the maximum difference
between each deviation within the set.
Depending upon the bearing size and class of precision the
maximum values for optimum load sharing with the set of
bearings is shown for both the bore and independently for
the OD of the bearings.
The bores of the bearings to be matched together into sets
are selected independently to the outer ring diameters.
NSK Super Precision Ball Bearings

79** 79
P2
Permissible difference of OD
P3
in a matched set (μm) The bearings are graded with the deviation in microns
P4
P2
from the nominal size.
Permissible difference of bore
P3
in a matched set (μm) Nominal
P4

OD grade
70** 70
P2
Bore grade
Permissible
difference
Permissible difference of OD from nominal
P3 dimensions
in a matched set (μm)
P4
P2
Permissible difference of bore
P3
in a matched set (μm) Nominal
P4

Nominal
Bore & OD matching chart

72** 72 Universal bearing matching

Permissible difference of OD
P2
P3
Super Precision ball bearings are made in accordance Permissible
with the International Standards Organisation’s
in a matched set (μm)
P4
dimension plans. All bearings in a set must be within difference
P2
Permissible difference of bore
in a matched set (μm)
P3 permissible bore & OD deviation from nominal from nominal
dimensions. This improves load sharing when bearings
dimensions
P4
are mounted closely.
73** 73
P2 The size difference of the OD and bore of sets of
Permissible difference of OD
P3 bearings is generally less than 1/3 of the size deviation.
in a matched set (μm)
P4
This chart can be used to identify the permissible
P2
Permissible difference of bore
P3 difference between OD’s and bores in a set of bearings
in a matched set (μm)
P4 for precision grades for P2, P3 and P4. Nominal

NSK Super Precision Ball Bearings

› For convenience ask NSK or your distributor to
79** 79
P2
supply the handy sliding chart which will enable
Permissible difference of OD
fast and accurate matching of all bearings within
P3
in a matched set (μm) The bearings are graded with the deviation in microns
P4
P2
from the nominal size.
Permissible difference of bore
in a matched set (μm)
P3
P4
Nominal the NSK range. This is a double sided pocket
70** 70 Permissible
difference
sized plastic coated chart.
P2
Permissible difference of OD from nominal
P3 dimensions
in a matched set (μm)
P4
P2
Permissible difference of bore
P3
in a matched set (μm) Nominal
P4

Bore & OD matching chart

72** 72 Universal bearing matching

P2 Super Precision ball bearings are made in accordance
Permissible difference of OD
P3 with the International Standards Organisation’s
in a matched set (μm)
P4
dimension plans. All bearings in a set must be within
84 Permissible difference of bore
in a matched set (μm)
P2
P3 permissible bore & OD deviation from nominal
P4 dimensions. This improves load sharing when bearings
are mounted closely.
Bore and OD Matching Chart
P2 P3/P4 P2 P3/P4

OD Bore OD Bore OD Bore OD Bore

7900 2 1 2 2 7000 2 1 2 2

7901 2 1 2 2 7001 2 1 2 2

7902 2 1 2 2 7002 2 1 2 2

7903 2 1 2 2 7003 2 1 2 2

7904 2 1 2 2 7004 2 1 2 2

7905 2 1 2 2 7005 2 1 2 2

7906 2 1 2 2 7006 2 1 2 2

7907 2 1 2 2 7007 2 1 2 2

7908 2 1 2 2 7008 2 1 2 2

7909 2 1 2 2 7009 2 1 2 2

7910 2 1 2 2 7010 2 1 2 2

7911 2 2 2 2 7011 2 2 2 2

7912 2 2 2 2 7012 2 2 2 2

7913 2 2 2 2 7013 2 2 2 2

7914 2 2 2 2 7014 2 2 2 2

7915 2 2 2 2 7015 2 2 2 2

7916 2 2 2 2 7016 2 2 3 2

7917 2 2 2 2 7017 2 2 3 2

7918 2 2 3 2 7018 2 2 3 2

7919 2 2 3 2 7019 2 2 3 2

7920 2 2 3 2 7020 2 2 3 2

7921 2 2 3 2 7021 2 2 3 2

7922 2 2 3 2 7022 2 2 3 2

7924 2 2 3 2 7024 2 2 3 2

7926 2 2 3 3 7026 2 2 3 3

7928 2 2 3 3 7028 2 2 3 3

7930 2 2 3 3 7030 2 2 3 3

7932 2 2 3 3 7032 2 2 3 3

7934 2 2 3 3 7034 4 2 7 3

7936 2 2 3 3 7036 4 2 7 3

7938 4 2 7 4 7038 4 2 7 4

7940 4 2 7 4 7040 4 2 7 4

7942 4 2 7 4

7944 4 2 7 4

7948 5 2 8 4

7952 - - 8 7

7956 - - 8 7

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 85

 Supplementary Information
Bore and OD Matching Chart

Bore and OD Matching Chart

P2 P3/P4 P2 P3/P4

OD Bore OD Bore OD Bore OD Bore

7200 2 1 2 2 - - - -

7201 2 1 2 2 - - - -

7202 2 1 2 2 - - - -

7203 2 1 2 2 7303 2 1 2 2

7204 2 1 2 2 7304 2 1 2 2

7205 2 1 2 2 7305 2 1 2 2

7206 2 1 2 2 7306 2 1 2 2

7207 2 1 2 2 7307 2 1 2 2

7208 2 1 2 2 7308 2 1 2 2

7209 2 1 2 2 7309 2 1 2 2

7210 2 1 2 2 7310 2 1 2 2

7211 2 2 2 2 7311 2 2 2 2

7212 2 2 2 2 7312 2 2 3 2

7213 2 2 2 2 7313 2 2 3 2

7214 2 2 3 2 7314 2 2 3 2

7215 2 2 3 2 7315 2 2 3 2

7216 2 2 3 2 7316 2 2 3 2

7217 2 2 3 2 7317 2 2 3 2

7218 2 2 3 2 7318 2 2 3 2

7219 2 2 3 2 7319 2 2 3 2

7220 2 2 3 2 7320 2 2 3 2

7221 2 2 3 2

7222 2 2 3 2

7224 2 2 3 2

7226 2 2 3 3

7228 2 2 3 3

7230 4 2 7 3

86
Useful Tips

List of Tips in This Publication

Tip number Tip description Section Page number

1 Setting bearing high points Bearing Selection 13

2 P3 precision more cost effective Bearing Selection 17

3 Changing preload in spaced bearings Bearing Selection 21

4 Greasing precision bearing using syringe Pre-mounting 28

5 Measurement of components - room temperature Pre-mounting 30

6 Hot air gun for heating housings Mounting 32

7 Adjusting spindle assemblies for better runout accuracy Mounting 35

8 Cylindrical roller bearing-housing assembly Mounting 37

9 Simple guide for roller bearing preload calculation Mounting 41

10 Spacer method for tapered bore cylindrical roller bearing preload setting Mounting 43

11 ‘Running in’ safety checks Post-mounting 51

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 87

 Index

A E
Axial Stiffness 14, 20, 49 End Cover Gap/Clearance 36-37
Axial Clearance 19, 24 EP Steel 58
Assembly Procedures 34
Alignment 50 F
F and B Mark on the Bearing Box 13
B Face to Face Arrangements 16
Bearing Overview 9 Fitting Area 26
Ball Screw Support Bearings 10 Bearing Fitting 32-33
Bending Stiffness 14 Failure, Causes of Failures, Countermeasures 70-74
Built-in Motors 15
Back to Back Arrangements 16
G
Bearing Combinations 20
Grease Lubrication 27
Bearing Capacity 20
Grease Quantity 28-29
Bearing Rigidity 20-21
Gauge Method for Mounting Cylindrical Roller Bearings 42-43
Bearing Matching Chart 24, 85-86
Bearing Tolerances 24
H
Balancing 50
High-Speed Bearings 9
Box Bar Code 24
High Point Marking 13
Handling Bearings 26
C Housing Measurements 30
Conventional Bearings 9
Induction Heater 33
Cylindrical Roller Bearings 10
Hybrid Bearings 63
C mark on Bearing and Box 13
Contact Angle 14
Constant Preload 18 I
CA Values 19 Introduction 4-5

Cr Values 20 Identification Marks 13

Cor Values 20 Interchange Guide 68

Contamination 26
Cleanliness 27 L
Component Checks 30 Life Ratio - Cylindrical Bearings 23
Calculation Method for Preload of Cylindrical Bearings 35-41 Locknut Torque 34
Couplings 50
Ceramic Balls 63 M
Cage Material 64 Material Upgrades 58

D N
d and D Marks on Bearing and Box 13 Natural Frequency 49
dmn Factor 19 Noise, Cause of 53
DU Arrangements 24
DUD Arrangements 24
Dismantling Area 26

88
P T
Product Range 6-8 Thrust Angular Contact Bearings 11
Precision Grades 17 Tandem Arrangements 16
Preload 18-23 Tolerances 17, 24
Position Preload 18 Taper (Cylindrical Roller Bearing) 35
Preload Adjustment - AC Bearings 20 Temperature, Cause of 52
Preload Adjustment - Cylindrical Bearings 22 TB Cage 66
Packaging 27 TYN Cage 64
Press Fits 33 TAC Thrust Bearing Conversion 65
Preload Checking 48-49 Thrust Bearings 65
Preload Conversion 78-83 Trouble Shooting 75-77

Q U
QU Arrangements 24 Universal Bearing Sets 16
Upgrading 54-55
R Useful Tips 87
Robust Bearings 9, 56-57
Radial Stiffness 14, 20 V
Runouts 17 Vee Lining - Single Bearing 13
Radial Internal Clearance (RIC) 22 Vee Lining - Sets of Bearings 13
Retaining Cover Tightening 36 Vee Drives 50
Running In Process 51
X
S X Type Bearing 56
Serial Number 13
Single Micron Grading 17 Z
Spring Preload 18 Z Steel 58
Speed Factors 18
Spindle Arrangements 16
Sliding Chart 24
Spacers 30
Shaft Measurements 30
Spindle Checks 34
Spindle Examples 44-47
Start Up Checks 52
SHX Material 58
Sealed Bearings 59-60

MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 89

 Notes

90
MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 91
 Notes

92
MACHINE TOOL SPINDLE BEARING SELECTION & MOUNTING GUIDE 93
 NSK Sales Offices – Europe, Middle East and Africa

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any errors or omissions. © Copyright NSK 2012. The contents of this publication are the copyright of the publishers.
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