B-3-3.

8 ND Series for Nut-Rotatable Drives

• This product is patented by NSK. 2. Features (2) Accuracy grade and axial play A Critical speed nc
A Multi-nut drive The available standard accuracy grade and axial As shown Fig. 4, calculate unsupported length
A nut rotatable ball screw is developed as a unit Two or more nut units can be installed in a play are as follows. Please consult NSK for other (mm) of L1, L2, and L3 (assumed that the nut section
into which angular contact support ball bearings single ball screw shaft. They can be operated by grades. is a fixed support.) Table 4 shows the coefficients
are integrated. It is best suited for an application respective motors. "f " of each shaft end mounting condition.
that requires rotation of the ball nut while the A High operation speed Table 1 Axial play d
nc = f • r2 × 107 (min-1) (3-1)
screw shaft is fixed. High feeding speed operation, but yet low Li
Axial play code Z T S
rotational speed, is feasible by means of dr: Screw shaft root diameter (See the
Axial play 0 0.005 mm or less 0.020 mm or less
NDT model medium to high-helix lead ball screws. dimension table.)
1. Structure A Easy installation Li : Unsupported length (mm) (See Fig. 4)
Balls are installed between the assembly Table 2 Combination of accuracy grades and axial play f : Factor determined by the ball screw shaft
Merely install a mount housing to the table of
housing and the ball nut. The outer bearing the machine to take advantage of this multi-nut Accuracy grade C3 C5 Ct7 end mounting condition
rings are integrated into the assembly housing rotation system. Axial play code Z, T, S Z, T, S S Table 4
and thus, compact design are attained. A Simple shaft end configuration Shaft end mounting condition f
A timing pulley (prepared by the user) is directly Shaft end configuration is simple because this
Fixed -- Fixed support 21.9
secured to the end face of the nut. unit does not need support bearings. 4. Allowable d•n value and the criterion
of maximum rotational speed Fixed -- Simple support 15.1
A Shaft diameter/lead combination
Timing pulley Assembly housing There are 10 types of "shaft diameter/lead" Allowable d·n value and the criterion of Fixed -- Free support 3.4
(shall be provided by the user) (fixing part)
combinations. maximum rotational speed are shown below.
Selections are: Shaft diameters -- 32, 40, 50 mm; Please consult NSK if the rotational speed
Leads -- 20, 25, 32, 40, 50 mm. exceeds the permissible range below.
A Low inertia Note: The basic concept is the same as that of

ND Series
Compared to the NSK current product (end cap general ball screws. Refer to "Technical
ball recirculation system), rotational inertia was Description: Permissible Rotational Speed"
reduced by 16% at most. (page B47).

Table 3 Allowable d•n value and the criterion of Fig. 4 Installation example
Ball nut Ball return tube 3. Specifications maximum rotational speed
(rotational part)
(1) Ball recirculation system 5. Design precautions
Standard
Fig. 1 Ball nut structure The structure of return tube recirculation system specification 70 000 or less One end of the screw thread should be cut-
Allowable d·n value High-speed
is shown below. specification 100 000 or less
through to the end. Also, if the nut must be
removed from the screw shaft, the user should
Criterion of maximum rotational speed 3 000 min-1
Slide table Assembly housing (fixed support) have an arbor to prevent the balls from falling
d·n value: shaft dia. d [mm] × rotational speed n [min–1]
out during this process. (NSK manufactures
Return tube Screw shaft
arbors on request.)
Timing pulley Ball screw nut (rotational)
(ball nut)
Ball screw shaft
For general precautions regarding ball screws,
(stationary) refer to "Design Precautions" (page B80) and
"Handling Precautions" (page B99).

Drive motor

Timing pulley Fig. 3 Structure of ball return tube recirculation

(drive motor)
system
Fig. 2 Example of installation to the table

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 NDD Type: (Incorporating vibration damper) 2. Features
An increase in stroke length may restrict A No need for measures against critical speed.
required rotational speed of a ball screw due Conventionally, an increase in screw shaft
to the issue of critical speed even if there is no diameter or use of intermediate support is the
problem on d·n limitation. measure against the issue of critical speed.
In such a case, we recommend using NDD NDD Type ball screw will make these measures
Type nut rotatable ball screws equipped with needless.
vibration damper. A Dimensional interchageability with NDT Type
It will make it possible to operate a ball ball screws
screw exceeding the critical speed, which is The vibration damper is set inside a ball screw
conventionally considered being impossible. shaft, and therefore, there is no difference
Notes: 1) However, NDD Type cannot be used with existing series in regards to external
exceeding the d·n limitation. Please dimensions. The ball nuts of NDD Type are
consult with NSK in such a case. interchangeable with those of NDT Type.
2) You cannot rotate the screw shaft of A Others
NDD Series. Benefits in multiple ball nut on a screw shaft,
high feeding speed for long stroke, easy in (Without vibration (With vibration
1. Structure installation, and low inertia of the ball nuts are damper) damper)
Hollow ball screw shaft has a mechanism to the same as NDT Type.
absorb vibration energy (vibration damper).
This increases dynamic rigidity of the screw 3. Specification
shaft and lowers vibration when exceeding the Recirculation system, accuracy grade, axial play
critical speed. and preload system are the same as NDT Type. Fig. 6 Vibration of screw shaft when nut is rotating

ND Series
Construction of the ball nuts are the same as 4. Design precautions
those of NDT Type. They are the same as NDT Type.

5. Permissible rotational speed

The d•n value is the same as NDT Type.
You don’t need to consider the critical speed.

Shaft diameter : d
j50 j40 j32

4 000 5 000 Unusable zone even the vibration damper is equipped.

3 000
4 000
3 000 Limitated by d · n = 100 000
2 000 3 000 (High speed specification)
2 000
2 000 Limitated by d · n = 70 000
Zone for NDD Type (Standard)
Rotational speed

1 000 (Usable zone with

1 000 the vibration damper.)
1 000

Zone for NDT Type

(Usable zone even
no vibration damper.)

–1
(min )
Limitation by the critical speed
100 (fixed – fixed support) (Without vibration damper) (With vibration damper)
100
100 j32
1 000 2 000 3 000 4 000 Fig. 7 Effect of vibration damper (results of endurance test)
j40 Shaft diameter: d
2 000 3 000 4 000 5 000

j50
2 000 3 000 4 000 5 000

Unsupported length L i (mm)

Fig. 5 Compartmentalization between NDT and NDD types to rotational speed and unsupported length
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 Calculation example of permissible rotational speed Structure of reference number
The followings describe the structure of "Reference number for ball screw".
[Calculation example] A Calculate critical speed
Assume a system which moves two nuts on a The maximum unsupported length comes
shaft as shown below. between Nut A and B.
Does this system operate appropriately if: both L2 = 3 300 (mm)
ends of the ball screw (shaft diameter 40 mm/ f = 21.9 (Fixed-Fixed) eReference number for ball screw
lead 40 mm) are fixed, and the travel speed is at Root diameter: dr = 35.1 (mm)
60 m/min? Therefore, the permissible rotational speed is; W 40 15 - ——
—— —— ——
** P
— —
XU - C5
— ———
Z
—— —
40
— ——
21.9 × 35.1
n≤ 2 × 10 = 706 (min )
7 -1
Product code Lead (mm)
[Answer] 3 300
The rotational speed n (min–1) when the lead of Screw shaft diameter (mm) Axial play code: Z, T, S (page B20)
the ball screw is 40 mm, and the travel speed is The calculation indicates that the d • n value is at
Effective threaded length (in the unit of 100 mm)
at 60 m/min is: the safe level. But the critical speed exceeds the Accuracy grade: C3, C5, C7 (Ct7) (page B37 to B42)
60 × 103 limitation. However, with a vibration damper, Design serial number
n= = 1 500 (min-1) Appearance/specification code
40 the system can be operated at 1 500 min–1. Preload code: No code, Non-preload; P, P-preload (page B5) ("T" is added for NDD Type.)
A Calculate d • n value
As the d • n value of standard specification is 7 000,
therefore, the permissible rotational speed is;
70 000
n≤
-1
= 1 750 (min )
40

ND Series
L 1 = 300 Stroke of ball nut A: 3 000

Fixed support Fixed support

Fixed
Fixed support support
Ball nut A Ball nut B

300 Stroke of ball nut B: 3 000 L 3 = 300

Maximum distance between ball nuts L 2 = 3 300

Fig. 8 Calculation example of permissible rotational speed

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 ND Series for nut-rotatable drives

60
6-jX1 drill thru 60° ° Seal
jY1 c'bore, Z1 deep (both sides)

W1
PCD

jD rh7

jDh6
jd m

jd r
jA

jd
PCD
W2

4-M2 tap, t2 deep

(equally spaced)
T B F
L

Unit: mm

Shaft Ball Ball Root Effective turns of Basic load rating (N) Moment of Ball nut Ball nut dimensions Tap hole
dia. Lead dia. circle dia. balls inertia, ball nut mass PCD
Model No. Turns Nut entire Nut outside Flange outside Flange Nut Projection tube dimensions Bolt hole dimensions Bolt hole Tap hole dimensions
dia. × Dynamic Static J W length diameter diameter width length PCD
d l Dw dm dr Circuits Ca C0a (kg·cm2) (kg) L D A B F Dr T X1 Y1 Z1 W1 M2 t2 W2
NDT
3220-2.5 20 4.762 33.25 28.3 2.5×1 17 900 41 800 6.2 2.9 107 78 105 12 83 60 12 6.6 11 6.5 91 M6 12 50
NDD
NDT 96
3225-2.5 25 4.762 33.25 28.3 2.5×1 17 900 41 800 6.7 3.2 120 78 105 12 60 12 6.6 11 6.5 91 M6 12 50
NDD
32

ND Series
NDT
3232-1.5 1.5×1 11 500 24 800
NDD
32 4.762 33.25 28.3 6.2 2.9 107 78 105 12 83 60 12 6.6 11 6.5 91 M6 12 50
NDT
3232-3 1.5×2 18 900 44 600
NDD
NDT
4025-2.5 25 6.35 41.75 35.1 2.5×1 28 500 70 000 19.3 6.0 136 100 133 15 106 76 15 9 14 8.5 116 M8 16 62
NDD
NDT
4032-1.5 1.5×1 18 400 41 200
NDD
32 6.35 41.75 35.1 18.0 5.5 122 100 133 15 92 76 15 9 14 8.5 116 M8 16 62
NDT
4032-3 40 1.5×2 30 100 74 100
NDD
NDT
4040-1.5 1.5×1 18 400 41 200
NDD
40 6.35 41.75 35.1 19.2 6.0 136 100 133 15 106 76 15 9 14 8.5 116 M8 16 62
NDT
4040-3 1.5×2 30 100 74 100
NDD
NDT
5025-2.5 25 7.938 52.25 44.0 2.5×1 42 700 109 000 45.7 8.5 140 120 156 18 107 96 15 11 17.5 11 136 M10 18 78
NDD
NDT
5032-2.5 32 7.938 52.25 40.0 2.5×1 42 700 109 000 48.9 9.4 158 120 156 18 125 96 15 11 17.5 11 136 M10 18 78
NDD
NDT
5040-1.5 1.5×1 27 500 66 500
NDD
50 40 7.938 52.25 44.0 45.5 8.5 140 120 156 18 107 96 15 11 17.5 11 136 M10 18 78
NDT
5040-3 1.5×2 44 900 120 000
NDD
NDT
5050-1.5 1.5×1 27 500 66 500
NDD
50 7.938 52.25 44.0 48.7 9.4 158 120 156 18 125 96 15 11 17.5 11 136 M10 18 78
NDT
5050-3 1.5×2 44 900 120 000
NDD
Notes: 1. The right hand screw is the standard. Consult NSK for the left hand screws.
2. Seals are standard equipment.

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