The ABC's of Gears

Basic Guide - B

The world's first 2WD Bicycle by SHESCO (includes KHK SB Bevel Gears)

1
S45

Hs38

0
Drawing is the first step to creating gear products.

06.10.28

SS-REI

KHK

A human powered aircraft (won a prize at the Birdman Competition, held in Japan)
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Contents
1. Gear Types and Characteristics
1-1 Parallel Axis Gears
1-2 Linear Motion Gears
1-3 Intersecting Axis Gears
1-4 Nonparallel and Nonintersecting

The ABC's of Gears include 3

editions; Introductory Guide,
Basic Guide, and Guide for
Practical Use.
This 'Basic Guide - B' introduces;
Types of Gears, How to Use
Gears, Basic Calculations for
Gears, Tooth Profiles, Shifting,
Accuracies, and Strength of
Gears.
To learn more about Gears,
please refer to the following,
Guide for Practical Use - C.

P 4
P 7
P 8

P10
2. Basic Terminologies and Calculations P12
3. Gear Tooth Profiles
P20
4. Profile Shifting

P22
5. Gear Accuracy

P24
6. Gear Materials and Heat Treatments
P26
6-1 Gear Materials
P26
6-2 Heat Treatments
P27
7. Strength and Durability of Gears
P28
8.Surface Treatment of Gears

P30
9.Manufacturing of Gears
P32
9-1 Manufacturing Process of Spur Gears P32
9-2 Manufacturing Process of Racks P33
9-3 Manufacturing Process of Bevel Gears
P34
9-4 Manufacturing Process of Worms P35
Axis Gears

Hello, I am Haguruma Boy!

Did you find the Introductory
Guide - A useful? I hope it
helped you learn about the
history of gears and their
usages.

P 2

The ABC's of GearsBasic Guide

1.Gear Types and Characteristics

In the following pages we present three general
gear categories corresponding to KHK Stock Gear
Classifications.
Categories of Gears

Types of Gears

Efficiency (% )

Parallel Axis Gears

Spur Gear

Helical Gear
98.099.5
RackHelical Rack

Internal Gear
Intersecting Axis Gears
Miter Gear

Straight Bevel Gear

98.099.0

Spiral Bevel Gear

Nonparallel and
Nonintersecting Axis Screw Gear
(Crossed Helical Gear)
Gears

70.095.0

Worm
30.090.0
Worm Wheel

--

Isometrics

1. Gear Types and Characteristics

There are so
many types
of gears.

KHK Stock Gears

MSGA

SSG

SS

SUS

PS

KHG

SH

KRG (F) (D)

SRFD

SUR (F) (D)

PR (F)

KRHG (F)

SI

SIR

MMSG

SMSG

MM

SUM

PM

SBCB
SBSBY

SB

SUB

PB

DB

MBSG

SBSG

MBSA (B)

SBS

SN

SUN

AN

PN

KWGDL (S)
AGDL

KWG AGF

SWG AG

SW BGCG

BGCG

--

SUW PG

The ABC's of GearsBasic Guide

Gear types are classified into 3 categories, generally by the directions of the
mounting shafts. Here, in this section, we introduce the characteristics of gears,
how to use gears, and technical tips (hints).

1 1 Parallel Axes Gears

Gears involving two axis, which are parallel to each other, are called Parallel Axis Gears. For the
transmission of rotation/power by parallel axis, Spur, Helical and Internal Gears are generally used.
These are the most commonly used gears, with a wide range of applications, in various industries.

Spur Gear
A spur gear is a cylindrical shaped gear, in which the teeth are parallel to the axis. It
is the most commonly used gear with a wide range of applications and is the easiest to
manufacture.

Characteristics / Technical Hints

A gear which is the most easiest to manufacture.
A gear that is easy to use and does not produce axial thrust forces.
There is no limit in the combination of the number of gear teeth
of paired gears.
Gear 1
(z1 , n1)

Gear 2
(z2 , n2)

Speed Ratio
In Figure.1.1, a pair of meshed gears in single-stage gear train.
As you can see, the rotational direction of the paired gears is opposite
to each other.
If Gear 1 rotates clockwise, then Gear 2 rotates counterclockwise.
Also, if paired gears have a different number of teeth, the
speed will be increased / decreased; If Gear 1 is a drive gear, speed is

Fig.1.1 Spur Gear

reduced. If Gear 2 is a drive gear, speed is increased.

No. of teeth of driven gear (z2)

Speed Ratio
No. of teeth of drive gear (z )
1

Rotation of drive gear

Rotation of driven gear

Calculation Example

(n1)
(n2)

.1

Gear 1

No. of teeth of drive Gear1 : 20

Rotation of gear

: 400rpm

No. of teeth of driven Gear2 : 80, Single-stage gear train.

The Speed ratio of this gear train : 8020=4
The rotation of Gear2 : 4004=100rpm

--

Gear 2

1. Gear Types and Characteristics

Helical Gear
The spur gear that has helix teeth (helicoids teeth) is called Helical Gear. Helical gears
can bear load more than spur gears and work more quietly. They are also widely used in
different industries, such as the automotive, and in industrial machinery.

Characteristics and Technical Hints

More strength than the spur gear of the same size; transmits rotational force / power quietly.
Suitable for use in high speed rotations.
Produces axial thrust force, need to cope with these extra forces
There is no limit in the combination of number of gear teeth of paired gears.
The direction of the rotation and the thrust force in meshed helical gears are illustrated in the Figure 1.2. Thrust
bearing receives thrust force. The direction of the rotation is the same as meshed spur gears.
Driven

Drive

Drive

Driven

Thrust bearing
Fig.1.2Direction of Rotation and Thrust Force
A paired gear rotates in opposite direction each other. The speed ratio is the same as it for spur gears.

Speed Ratio of Two-Stage Gear Trains

If Gear 1 is a drive gear, the speed ratio (i) for this twostage gear train is calculated as below.

n3
z
n1
z4
i z2
z3
n2 n4
1

Gear 4
(z4 , n4)

Gear 3
(z3 , n3)

Gear 2
(z2 , n2)

1.2

Gear 1 and Gear 4 rotate in the same direction. Number

of teeth of Gear 1/2/3/4 is 10/24/12/30, respectively,
then, the reduction ratio for this gear train is 6.

Fig.1.3Two-Stage Gear Train

--

Gear 1
(z1 , n1)

The ABC's of GearsBasic Guide

Internal Gears
This is a cylindrical shaped gear, but with teeth inside the circular ring, and can mesh with
a spur gear. Internal gears are often used in Planetary Gear Systems, or Gear Couplings.

Characteristics / Technical Hints

Involves more complexity in manufacturing compared, to spur gears.
By using planetary gear systems, it enables you to create a compact gear system applicable for
high reduction ratio.
For a pair of internal and external gears meshed, the following 3 interferences might occur:
(a) Involute Interference (b) Trochoid Interference and (c) Trimming Interference
No limit to the combination of the number of gear teeth, of paired gears.
Gear 2
(z2 , n2)

Speed Ratio
In the simplest example of a meshing External Gear 1 (Pinion) with

Gear 1
(z1 , n1)

an Internal Gear 2, both the External Gear 1 and Internal Gear 2 rotate
in the same direction, as shown in Fig, 1.4

No.Gear
of teeth
No. of Teeth of Driven

of Driven Gear
Speed Ratio
No. of teeth of Drive Gear

1.3
Fig.1.4 Spur Gear and Internal Gear

Planetary Gear Systems

Planetary Gear System consists of 4 major elements;

Internal gear C

Sun Gear (A), Planet Gear (B), Internal Gear (C), and Carrier (D)

z c = 48

Carrier D

In the system shown in Fig. 1.5, 4 planet gears are used.

The load division shared by many gears enables a compact system. The
speed ratio or the direction of rotation in the Planet Gear System differs,
depending on what factor is fixed.
aPlanetary Type
If the Sun gear is of input, and the Carrier gear
is of output, and the Internal gear is fixed;

z
Speed Ratio z c + 1
a

Sun gear A

z a = 16 Planet gear B
z b = 16

1.4

Fig.1.5 Example of a planetary gear system

bSolar Type

C(Fixed)
B

Sun Gear is fixed.

cStar Type

Carrier Gear is fixed.

(a) Planetary type

D(Fixed)

D
A(Fixed)

(b) Solar type

A
(c) Star type

Fig.1.6 Planetary Gear Mechanism

--

1. Gear Types and Characteristics

1 2 Gears with Linear Motion

Gears with Linear Motion are classified as Parallel Axis Gears, but there are specific types of
"Linear Motionthat involve no mating shafts. To convert rotational movement to linear motion,
or the converse, Racks and Pinions are used in combination. Cylindrical shaped gears with an
infinite radius are called Racks, generally used in conveyors.

Spur Rack
This is a linear shaped gear, which has a straight-line tooth profile and
can mesh with a spur gear. The spur rack can be regarded as a portion
of a spur gear with an infinite radius, and several racks can combined in a line.
Movement of one cycle of the CP10-30 pinion
on a CP rack vs.SS3-30 (m3) on a m3 rack.

Characteristics / Technical Hints

Easier to manufacture and to use than Helical Racks.

One turn
One half turn

Can mesh with a spur gear with any number of teeth.

In regards to a meshed rack and pinion, the movement distance
when the pinion rotates one time, is calculated from the number
of teeth multiplied by the pitch. Pitch denotes the distance
between corresponding points on adjacent teeth. CP racks are
designed for easy positioning. ( Figure 1.7 )

Pitch

Helical Rack

Fig.1.7 Difference between CP10 and m3

This is a linear shaped gear that meshes with a helical gear. A helical
Rack can be regarded as a portion of a helical gear with infinite radius.

Characteristics / Technical Hints

Produces thrust force; coping mechanism must be considered
Rotates and transmits power more quietly than a helical rack of the same size
Suitable for use in high speed rotation
Can mesh with a helical gear with any number of teeth
It produces thrust force due to the gear-tooth helix. The Figure 1.8 shows the direction of rotation and the thrust
force.
R Rack
Thrust

L Pinion
Thrust

Drive

L Pinion
Thrust

R Pinion
Thrust

L Rack
Thrust

R Pinion
Thrust

R Rack
Thrust

Drive

Fig.1.8 Direction of Rotation and Thrust Force

--

The ABC's of GearsBasic Guide

1 3 Intersecting Axis Gears

Gears involving two axis crossing at a point are called Intersecting Axis Gears; general
applications include rotation / power transmission of Bevel gears. Bevel Gears with gear ratio of
1, are called Miter gears. Bevel Gears are classified as Straight-Bevel Gears or Spiral-Bevel Gears,
depending on the tooth form.

Straight Bevel Gear

This is a gear in which the teeth have tapered conical elements that have the same
direction as the pitch cone base line (generatrix). The straight bevel gear is both the
simplest to produce and the most widely applied in the bevel gear family.

Characteristics / Technical Hints

Easier to manufacture than Spiral Bevel Gears.
Ease of use, produces no thrust force in the negative direction.
The combination of the No. of teeth of paired gears is important. Those
gears produced in combination do not mesh with other bevel gears.

Fig.1.9 Direction of Rotation

Spiral Bevel Gear

A bevel gear that has spiral teeth with a helical angle, which is more complex
to manufacture, but offers advantages of higher strength and less noise.

Characteristics / Technical Hints

LH spiral

Suitable for use in high load / rotation. Better than Straight Bevel Gears
Axial thrust force should be carefully considered
Transmits rotational force / power more quietly than Straight Bevel Gears.

Convex
surface

Concave
surface

Since these gears are produced as a pair, in accordance with the number of

Tooth

RH spiral

teeth, they do not mesh with other gears, even if they have the same modules or

Concave
surface

pressure angles.

Convex
surface

Tooth

Fig.1.10 Contact Surface of Spiral Bevel Gears

Speed Ratio

Drive

No. of teeth of Driven Gear

1.5
Speed Ratio
No. of teeth of Drive Gear

Thrust force on Spiral Bevel Gear

The figure on the right shows the rotational

Drive

direction and thrust force for the mesh of spiral

bevel gears, with gear ratio more than 1.57. If
the pinion meshes with a convex tooth-face, it
produces thrust force in the

GreenRH
YellowLH

negative direction.

Blue Positive Thrust Force

Red Negative Thrust Force

Fig.1.11 Direction of Rotation and Thrust Force

--

1. Gear Types and Characteristics

Straight & Spiral Miter Gear

Gears which are used as a pair, with the same number of teeth, are called Miter Gears.
There are two types of miter gears; a miter gear of straight bevel gears, and the other
is a miter gear of spiral bevel gears. Generally, they have a shaft angle of 90 degrees,
however, KHK offers standardized angular miter gears with the shaft angle at 45, 60, and
120 degrees.

Characteristics / Technical Hints

Bevel gears with the gear ratio at 1 is deemed a Miter Gear
Used for changing rotational or axial directions

Drive

Thrust Force on Spiral Miter Gears

The Figure 1.12 shows the rotational direction and the thrust
force on spiral miter gears. In case they produce thrust force
in a negative direction as well as in a positive direction, the
bearings must be positioned carefully so they can receive the
forces evenly.

Drive

GreenRH
YellowLH

Blue Positive Thrust Force

Red Negative Thrust Force

Fig.1.12 Direction of Rotation and Thrust Force

Angular Miter Gears and Miter Gears

Shaft Angle 45

Shaft Angle 60

Shaft Angle 90

Fig.1.13 Shaft Angles of KHK Stock Gears

--

Shaft Angle 120

The ABC's of GearsBasic Guide

1 4 Nonparallel and Nonintersecting Gears

Gears involving two axis, which are not intersected or parallel, are called Nonparallel and
Nonintersecting Axis Gears. They are generally used as worm gear pairs or screw gears. These
gears transmit rotational force/power by the relative slippage between gear-tooth surfaces.

Screw Gear (Crossed Helical Gear)

This is a helical gear with a spiral angle at 45 degrees. A pair of gears, nonparallel and are
nonintersecting and have the same helix hands, are called screw gears. They work very
quietly, but, can only be used for light loads.

Characteristics / Technical Hints

Care should be taken for lubrication. The slippage of the meshed faces transmits
rotational force / power. Lack of proper lubrication may cause rapid wear.
Efficiency is low when compared to parallel axis / intersecting axis gears.
Used in low power transmission
There is no limits to the no. of teeth of paired gears. (differing from Bevel Gears)
The direction of rotation and thrust force on right-helical (R) / left-helical (L) combinations are shown in the
Figure 1.14.

Driven

R helical
combination

Driven

Driven

Drive

Drive
Thrust bearing

Thrust bearing

Driven

L helical
combination

Driven

Drive

Drive

Fig.1.14 Direction of Rotation and Thrust Force

Speed Ratio
This formula for the speed ratio is the same as it for spur gears.
No. of teeth of Driven Gear

Speed Ratio
No. of teeth of Drive Gear

1.6

- 10 -

Drive

1. Gear Types and Characteristics

Worm Gear Pair

A Worm Gear pair is a set of gears, where one gear is a worm having screw threads and the
other is a meshed worm wheel. Worm gear pairs are often used in power transmission with highreduction or high-torque.

Speed Ratio
No. of teeth of Worm Wheel
Speed Ratio
Threads of Worm

1.7

The direction of rotation and thrust forces on right-helical (R) / left-helical (L) worm mesh, are shown in Figure 1.15.

R helical

Driver

Thrust bearing

L helical

Driver

Driver

Thrust bearing

Driver

Fig.1.15 Direction of Rotation and Thrust Forces

Characteristics / Technical Hints

Large reduction ratio can be obtained by a single-stage train
Efficiency is low if compared with parallel-axis gears or intersecting-axis gears
Worm gear pairs must be designed and produced as a pair. Gear-cutting is applied by a selective
cutting machine in accordance with the base diameter of the meshing worm.
As with screw gears, slippage occurs on the tooth surface of gears in mesh. Care should be
taken for lubrication. Lack of proper lubrication may cause rapid wear.

Calculation Example
Threads of the worm z1 = 2 , No. of teeth of the worm wheel z2 = 40

Speed Ratio

40
20
2

- 11 -

The ABC's of GearsBasic Guide

2. Basic Gear Terminology and

Calculations
Let's learn the basics of Basic Gear Technology!
Gear size, pressure angle, number of teeth...we introduce the basic terminology,
measurement, and relational expressions necessary to understand basic gear technology.
Comparative Size of Gear-Teeth
Using ISO (International Organization for Standardization)
guidelines, Module Size is designated as the unit representing

m=1

gear tooth-sizes. However, other methods are used too.

Module (m)
m = 1 p = 3.1416
m = 2 p = 6.2832
m = 4 p = 12.566

m=2
m=4
Fig.2.1 Tooth Profiles of Racks



If you multiply Module by Pi, you can obtain Pitch ( p ). Pitch is the distance between corresponding points on
adjacent teeth.

p Pi Module m

2.1

Calculation Example
What is the pitch size (

p ) of the Gear with module m = 3 ?

p = m = 9.4248

CPCircular Pitch
Circular Pitch (CP) denotes the reference pitch ( p ).
For instance, you can produce gears at an exact integral value, such as CP5/CP10/CP15/CP20.
Transformation from CP to Module

m=

CP

Calculation Example
CP10 is transformed to module as follows;

m =

10
=3.1831
3.1416
- 12 -

2.2

2. Basic Gear Terminology and Calculations

DPDiametral Pitch
DP stands for Diametral Pitch.
By ISO standards, the unit Millimeter (mm) is designated to express length, however, the unit inch is used in the
USA, the UK and other countries; Diametral Pitch is also used in these countries
Transformation from DP to Module

m=

25.4
DP

2.3

Calculation Example
DP 8 is transformed to module as follows;

25.4
8

m=

= 3.175

Pressure Angle
Pressure angle is the leaning angle of a gear tooth, an element determining the tooth profile.
Recently, the pressure angle is usually set to 20, however, 14.5 gears were prevalent.

ure Normal reference line

Pressle
g
Pitch
an

Reference line

Top land

Tooth
surface

Root surface
Fig.2.2 Normalized Tooth Profile of Reference

No. of teeth

10

No. of teeth denotes the number of gear teeth.

They are counted as shown in the Figure 2.3. The number
of teeth of this gear is 10.

Fig. 2.3 No. of teeth

Module ( m ) , Pressure Angle ( ) , and the No. of Teeth, introduced here, are the three basic elements in the
composition of a gear. Dimensions of gears are calculated based on these elements.

- 13 -

The ABC's of GearsBasic Guide

Tooth Depth and Thickness

Tooth depth is determined from the size of the module ( m ). Introduced here are Tooth Profiles (Full depth)
specified by ISO and JIS (Japan Industrial Standards) standards.
Please see Figure 2.4 below for explanations for Tooth depth h / Addendum ha / Dedendum hf .
Tooth depth h is the distance between tooth tip and the tooth root.

2.4

h = 2.25 m
Addendum + Dedendum
Pitch

Tooth
thickness

Addendum

Reference
line

Dedendum

Fig. 2.4 Tooth Depth and Thickness

Tooth Depth

Tooth tip

Tooth root

Addendum ha is the distance between the reference line and the tooth tip.

ha = 1.00 m

2.5

Dedendum hf is the distance between the reference line and the tooth root.

hf = 1.25 m

2.6

Tooth thickness s is basically half the value of pitch ( p ). * Pitch ( p ) m

s=

m
2

2.7

Calculation Examples
The following are calculations of Tooth depth (h) / Addendum (ha) / Dedendum (hf)for a gear with module 2.

h = 2.25 m = 2.25 2 = 4.50

ha = 1.00 m = 1.00 2 = 2.00
hf = 1.25 m = 1.25 2 = 2.50

- 14 -

2. Basic Gear Terminology and Calculations

In the previous pages, we introduced the basics of gears, includingModule,Pressure Angle,Number of
Teeth' andTooth Depth and Thickness. In this section we introduce the basic parts of Spur Gears (Cylindrical
gears) and dimensional calculations.

Diameter of Gears (Size)

The size of gears is determined in accordance with the reference diameter d and determined by these other
factors; the base circle, Pitch, Tooth Thickness, Tooth Depth, Addendum and Dedendum.

Addendum
2.8

d=zm

Dedendum

er
et
am

nc
re

Re

df d 2.5 m

2.10

ter

me

ia
ip d

fe

Ro

Root diameter df

di

ot

dia

2.9

da = d + 2 m

me

ter

Tip diameter da

Reference diameter

ig.2.5 Diameter of Gears

The Addendum and dedendum circle introduced here are a reference circle that cannot be seen on a gear, as
it is a virtual circle, determined by gear size.

Calculation Examples
The following are calculations of Reference diameter / Tip diameter /
Root diameter for a spur gear with module(m) 2, and 20 teeth(z).

d = z m = 20 2 = 40
da = d + 2 m = 40 + 4 = 44
df = d2.5 m = 40 5 = 35

Practice Test
Spur Gear Specifications
Module
m= 4 No. of teeth
z= 40 Pressure angle
Reference diameter

Tip diameter

da =

Root diameter

df

= 20

=
5')#/+

KHK

- 15 -

The ABC's of GearsBasic Guide

Tip d
iame
ter
Refer
ence
diam
eter
Base
diam
eter
Root
diam
eter

Facewidth
Tooth
thickness

p
Ti

ot

Reference
pitch

di

am

dia

et

et

er

er

er

se

et

Ba

am
di

Ro

Pressure Angle
Center line
Tip and Root
Clearance

ash

ckl

Ba

Pressure Angle

ce

Dedendum

To

ot

am

di

er

et

n
re

fe

hd

Re

ep

th

Addendum
Center distance

Fig. 2.6 Working Gear Nomenclature

Table 2.1 Gear Symbols and Nomenclature

Terms
Module
Pressure Angle
No. of Tooth
Pitch
Tooth Depth
Addendum
Dedendum

Symbols

z
p
h
ha
hf

Terms
Symbols
s
Tooth Thickness
d
Reference Diameter
da
Tip Diameter
df
Root Diameter
a
Center Distance
j
Backlash
c
Tip and Root Clearance
- 16 -

2. Basic Gear Terminology and Calculations

Center Distance and Backlash

When a pair of gears are meshed so that their reference circles are in contact, the center distanceais half the
sum total of their reference diameters.

Center distancea

d2
a=

(d1+d2)
2

d1

2.11
Fig. 2.7 Center distance

Gears can mesh as shown in the Figure 2.6, however, it is important to consider a proper backlash (play) so that
the gears can work smoothly. Backlash is a play between tooth surfaces of paired gears in mesh.
Mating gears also have a clearance (play) vertical to tooth depth. This is called Tip and Root Clearancec,the
distance between tooth root and the tooth tip of mating gears.

Tip and Root Clearancec

Dedendum circle

c = 1.25 m 1.00 m
= 0.25 m

2.12

Tip and Root

Clearance

Addendum circle

Fig. 2.8 Tip and Root Clearance

Calculation Examples
The following are calculations for Center distance
aand Tip and root clearance(c)
when ; Module

m 2 , Pinion z1 20, Gear z2 40

Reference diameter of Pinion d 1 = 20 2 = 40
Reference diameter of Gear d 2 = 40 2 = 80
Center distance a =

( 40 + 80 )
= 60
2

c = 0.25 2 = 0.5

- 17 -

The ABC's of GearsBasic Guide

Calculation Examples
Practice calculating the dimensions of gears.

Terms

Symbols

Module

2.5

Pressure Angle

20

No. of Teeth

Reference diameter

Addendum

Formula

Gear

Pinion

15

30

zm

37.5

75

ha

1.00 m

2.5

2.5

Dedendum

hf

1.25 m

3.125

3.125

Tooth Depth

2.25 m

5.625

5.625

Tip diameter

da

d+2m

42.5

80

Root diameter

df

d 2.5 m

31.25

68.75

Center distance

d1 + d2
2

56.25






Practice Test
Calculations for the dimensions of gears.

Terms

Symbols

Module

Pressure Angle

20

No. of Teeth

Reference diameter

zm

Addendum

ha

1.00 m

Dedendum

hf

1.25 m

Tooth Depth

2.25 m

Tip diameter

da

d+2m

Root diameter

df

d 2.5 m

Center distance

d1 + d2
2

Formula

12

- 18 -

Gear

Pinion

60

2. Basic Gear Terminology and Calculations

He

Helical Gear

lix

Spur gears with helicoid teeth are called Helical Gears.

an

gle

The majority of calculations for spur gears can be applied to

helical gears too. This type of gear comes with two kinds of tooth
profiles in accordance with the datum surface. (Figure 2.9)
(a) Transverse System (Transverse module / Pressure angle)

NOTE 1

(b) Normal System (Normal module / Pressure angle)

NOTE 1. Transverse axis denotes the centerline of the gear.

or

Relational Expression: Transverse module( mt ) and Normal module( mn )

mt =

mn
cos

2.13

al

od

ul

Transverse
module

Fig. 2.9 Right-handed Helical Gear

Both systems are used in KHK Stock Gears.

Transverse SystemKHG Grounding helical gears
Normal SystemSH Helical gears
Reference diameter (d) of the helical gear with transverse system can be calculated from Equation (2.8).
Reference diameter (d) of the helical gear with normal system can be calculated from Equation (2.14).

d=

z mn
cos

2.14

Calculation Examples
The following is a calculation for the Reference Diameter of a helical gear with;

mt = 2, No. of teeth z = 30, Helix angle = 15(R)

Reference Diameter d = z mt = 30 2 = 60
Transverse module

The following is a calculation for the Reference Diameter of a helical gear with;

mn = 2No. of teeth z = 30, Helix angle = 15(R)

Reference Diameter d = z mn / cos = 30 2 / cos 15 = 62.117

Normal module

Practice Test
Specifications for a helical gear
Normal module

( mn ) = 4

Transverse module

Helix angle

mt

( ) = 15

- 19 -

The ABC's of GearsBasic Guide

3. Gear Tooth Profiles

One of the most popular tooth profiles is the Involute
Tooth Profile.
The majority of gears used in industrial machinery are gears with an involute tooth
profile. The popularity of the involute tooth profile is derived from many of it's
advantages, such as simplicity in design and ease of use.
Characteristics of Involute Tooth Profiles
1. Easy machining for production (Straight rack tooth profile)
2. Rotation is smooth despite changes occurring in the center distance.
3. Gears with different number of teeth can be modified by machining if they have the same module and the
pressure angle.

d
b
A

What is an involute Tooth Profile?

Involute tooth profile (Involute curve) is a curve made by a base circle (

db ). The definition of an involute is the spiraling curve traced by the end

of an imaginary taut string unwinding itself from that stationary circle

called the base circle. The resultant is the Involute curve A b c d

C
D
E

e, and so on.
Figure 3.1 shows the state of the curve when the straight line is rolled
down by 90 degrees (1/4 of the circle).

Fig. 3.1 Involute Curve

What is Base Circle?

The base circle is the base circle of the involute, and its value is determined depending on the sizes of the
pressure angle ( ) and the reference circle ( d ).

db = d cos

3.1

The Base circle is also the base circle of the involutes.

The Reference circle is the actual reference that determines the size of the gear.
Dimensions of both the base circle / reference circle are crucial for gearing.
An Involute tooth profile is the curving line created external to the side of the base circle.
The value of the pressure angle becomes O (zero) on the base circle.

- 20 -

3. Gear Tooth Profiles

Meshing of Involute Gear

A pair of standard involute gears mesh

Gear

Gear

together between the reference Center

d2

Distance, making contact at a point

d1

on the reference circle of each other.

Reference circle

This state resembles friction wheels with reference

diameter's, d 1 and d 2. However, involute gears
actually mesh based on the base circle, instead of
the reference circle, resembling a rotation/power

Center Distance

transmission by using a cross-coupled belt placed

around the 2 base circles.
In case of a belt drive, slippage tends to occur

db

when frictional force gets smaller than power

d b1

transmission. However, in case of gears, they can

transmit rotation/power without slippage as they

Reference circle
A

have teeth.
The common tangent of the two base circles

Re

fe

Look at the yellow teeth of the drive gear in the

figure on the right, after the tooth begins to mesh,

le

rc

irc

ot

Ci

eC

P1

rotation by meshing two teeth and one tooth,

Driven Gear

moves to P3 and the next tooth P1 starts meshing, so

two teeth mesh again. Therefore, the gear transmits

P2

further movement of the drive gear, the contact point

Drive Gear

when the contact point on the two base circles moves

to point P 2 , it meshes with one more tooth. With

as

P3

two of the teeth are kept in meshP1/P3. Then,

Ro

re

nc

common tangent of these two base circles.

BB

eC

irc

le

line of action. The contact point P1 P2

P3 of the two involutes slide along the

le

Fig. 3.2 Power Transmission

(A and B) is called the line of contact, or

alternately and

Tan

gen

t Li
n

eA

repeatedly.

Fig. 3.3 Meshing of Involute Gear

- 21 -

The ABC's of GearsBasic Guide

4. Profile Shifting

Usage of profile-shifted gears enables more strength,

by adjusting the center distance.
When you use gears, you might find a situation that you need to adjust the center
distance to create more strength. In this section, we introduce profile shifting by
changing tooth profile, or tooth thickness.
1.57
Gears are divided into two types, one is a standard gear, and the other is a
profile-shifted gear. Standard gears have a basic tooth profile as shown in
Figure 4.1. Profile shifting is applied to create gears with tooth thickness that
is different from standard gears. By making the tooth thickness of involute

1.0
1.25

gears thicker or thinner, you can change gear strength and the center
distance of paired gears.
Fig. 4.1 Tooth profile of
a rack with Module 1

Number of Teeth and Tooth Profiles

Although the tooth profile of racks is straight, the tooth profile of involute gears differs depending on the number
of teeth. Involute tooth profile is curvilinear, but becomes straighter like the tooth profile of a rack, if the number
of teeth is increased.

z = 10

z = 100

z = 20

z = 200

Fig. 4.2 Tooth profiles varied by number of teeth

When the number of teeth is increased, the tooth profile gets thicker at the tooth-root and can generate more
strength. As for the tooth profile of a 10-teeth gear, it is gouged at the tooth-root and under-cutting occurs.

Small

No. of Teeth

Large

Small

Tooth Thickness
at Root

Large

Small

Strength

Large
Fig. 4.3 Comparison of
Tooth Profiles : z10 z200

By applying a positive correction and increasing the tip diameter and thickness, 10-teeth gears can also obtain
the strength of a 200-teeth gear (z=200).

- 22 -

4. Profile Shifting
Rack Form Tool

Profile Shifted Gear

cutting is called the extra feed of gear cutter xm (mm).

xm Extra feed of gear cutter

d sin 2
2

(z =10). The amount of shift or correction made when applying gear

xm

Figure 4.4 shows gear cutting for a positive correction of 10-teeth gear

db
d

x Profile Shift Coefficient

m Module
As in Figure 4.5, if profile shifting (Profile Shift coefficient x = +0.5) is
applied, the tooth profile is changed and the tooth thickness increases.
Outside diameter (Tip diameter) also becomes larger. It is also notable
that positive correction is effective to prevent undercut. There are

Fig. 4.4 Generation of

Positive Shifted Spur Gear

( = 20 , z = 10 , x = + 0.5 )

also other reasons for applying profile shifting, stated below.

Under
cut

Changing the Center Distance

Reference center distance of the standard gear (without shifting) is
the half value of the sum of reference diameters. Profile shifted gears
allow you to enlarge or reduce the center distance.

Fig. 4.5 Comparison with

Positive Shifted Tooth Profile

Positive correction Enlarge the center distance

d'

d'

Characteristics and technical hints for Profile Shifted Gears

Negative correction Reduce the center distance

There are limits in profile shifting, for both positive correction and
negative correction.

Positive Correction
Forms a tooth profile that has more bending strength, as the tooth
thickness becomes thicker at the root.
Contact ratio becomes smaller, as the working pressure angle
becomes larger by the increase of the center distance,

a'
Fig. 4.6 Center Distance of
Positive Shifted Gear

Tooth tip might be sharpen, more shifting is applied, the tooth

width at the tip gets smaller, and the tooth tip becomes sharpen if it
exceeds the limit in shifting.

Negative Correction
Forms a tooth profile that has less bending strength, as the tooth
thickness becomes thinner at the root.
Contact ratio becomes larger, as the working pressure angle
becomes smaller by the decrease of the center distance.
Undercut may occur, more shifting is applied, the tooth width at root
gets smaller, undercut occurs if it exceeds the limit in shifting.

- 23 -

Fig. 4.7 Pointed Tooth-tips

The ABC's of GearsBasic Guide

5. Gear Accuracy
High accuracy in a gear denotes a gear that will
produce less errors.

A gear must work in transmitting rotation/power from one gear axis to another,
efficiently and quietly. To improve gear accuracy is to improve the performance of a gear.
Gear accuracy can be loosely classified into 3 types
The datum of gear accuracy is the centerline (gear axis) of a gear
Higher accuracy gears have less errors
1Precision in involute tooth profile

Profile Deviation

2Precision in tooth face / tooth trace

Helix Deviation

3Precision in positioning of teeth / tooth-spaces

Precision in tooth positioning

Single Pitch Deviation

(Precision in pitch)

Total Cumulative Pitch Deviation

Variation of the position of a ball inserted

in each tooth space, around the gear

Runout Error of Gear Teeth

Pitc

h1
h

tc

Pi

10
Tooth trace

Tooth profile

4
7

Fig. 5.1 Gear Accuracy

Helix DeviationF

Profile DeviationF
Dedendum

L
LAE
LAF

L :Evaluation range
LAE :Active length
LAF :Usable length

L
b

L :Evaluation range
b :Facewidth

Design helix

Designed profile
Actual profile
Fig. 5.2Total Profile Deviation

Addendum

Actual helix
Fig. 5.3Total helix deviation

F
- 24 -

5. Gear Accuracy

Pitch Deviation

+ fpt

pt

The pitch value is measured on a measurement-circle where

the center is the gear axis.

+F

aSingle Pitch Deviation fpt

The deviation between actual measurement pitch value and

pt

pk

------ Theoretical

theoretical circular pitch.

Actual

Fig. 5.4Pitch Deviation

bTotal Cumulative Pitch Deviation Fp
Evaluated by measuring the accumulative pitch deviation of the total amount of gear teeth, where the overall
amplitude of accumulative pitch error curve is the total cumulative pitch deviation.

Fr

Runout Error of Gear Teeth Fr

Runout error is measured by indicating the position of a pin or

Eccentricity

ball inserted in each tooth space around the gear and taking
the largest difference. The values of runout include eccentricity.

Total Radial Composite Deviation Fi

Tooth profile / Pitch / Tooth space are factors to evaluate

1 2

10 12

14 16 1

Number of tooth space

Fig. 5.5Runout error of a 16-tooth gear

gear accuracy by measuring a single gear. There is also

another method to evaluate gear accuracy, which is the double flank meshing test method; a measurement of a
gear meshed with the master gear. This method measures the variation in the center distance when the gear is
rotated one revolution, in a tight mesh with a master gear.
Figure 5.6 is the test result for the 30-tooth gear. It shows 30 small mountain-like waves, representing the toothto-tooth radial composite deviation. The value of total radial composite deviation would be similar to the sum of
runout error and tooth-to-tooth radial composite deviation.

Total radial composite deviation

Tooth-to-tooth
radial composite deviation


Fig 5.6 Test result of Total Radial Composite Deviation

- 25 -

The ABC's of GearsBasic Guide

6. Gear Materials and Heat Treatments

It is essential to select proper materials and heat
treatments in accordance with the intended application
of the gear.
Since gears are applied for various usages, such as industrial machinery, electric/
electronic devices, household goods and toys, and composed of many kinds of
materials, we like to introduce typical materials and their heat treatment methods.

6 1 Types of Gear Materials

S45CCarbon Steel for Structural Machine Usage

Heat Treatment and Hardness

Heat Treatment
Hardness
amounts of carbon (0.45% ). S45C is easily obtainable and is used in
None
less than 194HB
the production of spur gears, helical gears, racks, bevel gears and
Thermal Refining 225 260HB
worms.
Induction Hardening 48 53HRC
S45C is one of the most commonly used steel, containing moderate

SCM440 ( Chrome-molybdenum Alloy Steel )

Heat Treatment and Hardness
Heat Treatment
Hardness
than S45C and is used with thermal-refining or induction-hardening
Thermal Refining 225 260HB
treatment for producing gears.
Induction Hardening 50 55HRC
An alloy steel containing moderate amounts of carbon (0.40 % ). It
also contains chrome / molybdenum. SCM440 has more strength

SCM415 ( Chrome-molybdenum Alloy Steel )

SCM415 is one of the most commonly used low-carbon alloy steel (C = 0.15% ). Generally, it is carburized for use.
It has more strength than S45C or SCM440. Surface hardness should be between 55 and 60HRC for use.

SUS303 ( Stainless Steel18Cr-8Ni Stainless Steel

Since it is called "stainless steel", it is a rust-resistant steel. This authentic stainless steel is basically non-magnetic.
Most commonly used for gears in applications where rust contamination is undesirable, such as in food-processing
machinery. There is a similar stainless steel called SUS304 which has more corrosion resistance than SUS303.

Copper Alloy Casting

Frequently used as a material for worm wheels. Phosphor bronze casting (CAC502) or aluminum-bronze casting
(CAC702) are commonly used. For mating worms, iron metals such as S45C/SCM44/SCM415 are used. To
prevent galling / seizure by slippage, different materials are used for each of the paired worm and worm wheel.

- 26 -

6. Gear Materials and Heat Treatments

6 - 2 Heat Treatments
What is Quenching?

Quenching is a treat ment performed on steel, applying rapid cooling after heating at high temperature
(Approximate 800 C). Quenching is applied to adjust the hardness of steel. There are several types of quenching
in accordance with cooling conditions; oil quenching, water quenching, and spray quenching. After quenching,
tempering must be applied to give toughness back to the steel, that might become brittle. Quenching cannot
harden genuine steel, however, quenching can work for steel containing more than 0.35% carbon.

What is Thermal Refining?

Thermal Refining is a heat treatment applied to adjust hardness / strength / toughness of steel. This treatment
involves quenching and tempering. Since machining is applied to products after thermal refining, the hardness
should not be raised too high in quenching.

What is Induction Hardening?

Induction Hardening is a heat treatment performed to harden the surface of the steel
containing carbon more than 0.35% , such as S45C or SCM440. For gear products, induction
hardening is effective to harden tooth areas including tooth surface and the tip, however,
the root may not be hardened in some cases. The
Gear

precision of gears declines by induction hardening. To

encourage the gear accuracy, grinding must be applied.

High
Frequency
Inductor
(Coil)
Fig. 6.1 Quenching Machine

What is Carburizing?
Carburizing is a heat treatment performed to harden
only the surface of low-carbon steel. The surface, in

Fig. 6.2 Heating Coil

which carbon is present and penetrated the surface,

gets especially hardened. Inner material
structure (with low-carbon C = 0.15% ) is also hardened
by some level of carburizing, however, it is not as
hard as the surface. The precision of carburized
gears declines by 1 grade or so, due to deformation
(dimensional change) or distortion. To encourage the

Fig. 6.3 Carburizing Furnace

gear accuracy, grinding is essential.

What is Nitriding?
Nitriding is a heat treatment performed to harden the
surface by introducing nitrogen into the surface of

Fig. 6.4 Carbon layer by carburizing

steel. If the steel alloy includes aluminum, chrome, and molybdenum, it enhances nitriding and hardness can be
obtained. A representative nitride steel is SACM645 (Aluminum chromium molybdenum steel).

- 27 -

The ABC's of GearsBasic Guide

7. Strength and Durability of Gears

The tooth is the most crucial element of gears. Strength
of gears depends on the breakage durability or friction
durability.
Gear designers decide specifications in accordance with factors like torque,
rotation and expected lifetime. In this section, we briefly introduce the bending
Force
strength and the surface durability.
Bending Strength of Spur and Helical Gears JGMA401-01
As shown in the Figure.7.1, the tooth fillet breakage occurs at the root when
applied force exceeds the limit. The following is the equation for bending

Breakage

stress:

Allowable
Tangential Force Ftlim

Flim

Symbol Name

Flim
mn
b
YF
Y
Y
KL
KFX
KV
KO
SF

mn b
YF Y Y

KL KFX
KV KO

Fig. 7.1 Lack of

bending stress at root

1
7.1
SF

Affected Factors and other Specifications

Allowable bending stress at root Material / Heat treatment

Normal Module
Face Width
Tooth Profile Factor
Load Sharing Factor
Helix Angle Factor
Life Factor
Size Factor of Root Stress
Dynamic Load Factor
Overload Factor
Safety Factor

Tooth size
Gear size
Pressure angle/ Profile shift coefficient / Tooth width
Contact ratio
Helix angle of helical gear
Expected lifetime
1.00 at the moment (unknown)
Circumferential speed / Gear accuracy
Motor / Impact from load
It should be set to more than 1.2 for safety considerations

How to encourage bending strength

To encourage bending strength, values in the equation for allowable tangential force
(7.1) should be set to; The value of denominator should be small & The numerator
should be large
a) Use durable materials (Increase allowable bending stress at root)
b) Enlarge the gear size (For large module / wide tooth width)
c) Strengthen tooth profile (Decrease tooth profile factor)
Large pressure anglePositive correction
d) Increase contact ratio (Decrease load distribution factor)
Small pressure angleLarge tooth depth
eImprove accuracy

- 28 -

7. Strength and Durability of Gears

Surface Durability of Spur and Helical Gears JGMA402-01

Tooth surface durability is calculated in accordance with the contact stress, to
figure out the strength against the tooth surface damage (Pitting).
The allowable tangential force Ftlim for surface durability is;
Fig. 7.2 Contact Stress

Allowable
2
Tangential Force Ftlim Hlim d01 bH

Symbol Name

Hlim

Allowable Hertz Stress

d01
bH
i
ZH
ZM
Z
Z
ZHL
ZL
ZR
ZV
ZW
KHX
KH
KV
K0
SH

Gear Ratio z2 / z1
Zone Factor
Material Factor
Contact Ratio Factor
Helix Angle Factor
Life Factor
Lubricant Factor
Surface Roughness Factor
Lubrication Speed Factor
Hardness Ratio Factor
Size Factor
Longitudinal Load Distribution Factor
Dynamic Load Factor
Overload Factor
Safety Factor

Pitch Diameter of Pinion

Effective Facewidth

i
i1

KHL ZL ZR ZV ZW KHX
ZH ZM Z Z

1
KH KV KO

1
7.2
SH2

Affected Factors and other Specifications

Material / Heat treatment

Pinion size (Diameter)

Gear size
Ratio of the number of teeth
Helix angle / Profile shift coefficient
Material combination
Transverse / Overlap contact ratio
1.00 (Assumed)
Expected lifetime
Lubricants and Viscosity
Surface roughness
Circumferential speed / Surface hardness
Hardness of wheels
1.00 assumed
Gear Support / Stiffness etc.
Circumferential speed / Gear accuracy
Motor / Impact from load
Set to more than 1.15 for safety considerations

How to increase surface durability

a) Use hard material treated by quenching ( Increase allowable hertz stress )
b) Enlarge gear size (Large pitch diameter / Wide effective tooth width )
c) Increase contact ratio (Decrease contact ratio factor )
d) Improve accuracy

The strength calculator on KHK web site

The calculation of gear strength tends to be rather complicated. On our web site, we offer a strength
calculator for KHK stock gears, which enables you to calculate gear strength automatically, by inputting
values in accordance with your usage condition. For gear strength calculation, there are several formulas. The
gear strength formula used in our calculator is based on JGMA (Japanese Gear Manufacturers Association)
specifications.

- 29 -

The ABC's of GearsBasic Guide

8. Surface Treatment
Surface treatment when properly applied in accordance
with usage conditions will improve the capabilities of
gears.
Surface treatments are performed to make surface condition improvements on
materials. The following are typical reasons for surface treatments, providing rust
prevention and inhibiting abrasion by friction, to improve overall quality control.
For corrosion resistance / For rust prevention
For wear resistance
For improvement in surface roughness
(Smooth surface)
For improvement in appearance
Others
(Improvement in fatigue strength, etc.)
Electro-galvanizing
A typical plating method applied to prevent the rusting of steel. By applying a

Electro-galvanizing

chromating process, the quality of the appearance also improves. Thickness of

plating film is generally between 2 to 25 m.

Uni-chromate
Silver white in color with slight bluish tint. The rust preventative properties are less
than electro-galvanizing but the price is lower.

Uni-chromate

Chromate
It has a multi-color appearance consisting of red, yellow and green. It has more
corrosion resistance than Uni-chromate.

Black-chromate

The color is basically black, but it looks slightly red depending on product
shapes. It has the most corrosion resistance of all 3 types of electro galvanizing.

Chromate

Electroless Nickel Plating

A plating method produced without the use of electricity. It inhibits corrosion/
wear resistance. This plating is suitable for products that have; uniform thickness
of plating film (310

m), complicated shapes, or high-precision is required.

Black-chromate

Electroless Nickel Plating

- 30 -

8. Surface Treatment

Black Oxide Treatment

A treatment from alkaline black oxidizing.
Applying a 140 heated, strong alkaline processing liquid, the material is blacken
by a chemical reaction within the steel. It is effective for rust proofing. On the
surface it makes a ferrosoferric oxide film, a thickness that is less than 3 m.
Black Oxide Treatment

Raydent Treatment
Raydent is a registered brand of Raydent Industrial Co., Ltd. Expect excellent rust
prevention performance from this treatment. The color is black and the processing
is similar to plating, as it makes a Raydent film (1 to 2 m) on the surface, which
is extremely strong and will not separate.

Phoshate Treatment

Raydent Treatment

A treatment from an Iron phosphate type coating.

An Iron phosphate type film is a thin amorphous film used as a base coating for
painted interior products.

PALFOS M
A treatment with manganese phosphate that produces a plating thickness
approximately 3 to 15 m. Used as a rust prevention film
and also applied to sliding components, as it is wear-resistant.

Solid Lubrication Treatment

A dry-coating spray, very useful as a solid lubrication treatment, where direct

PALFOS M

application of lubrication is not possible.

Achieved by spraying on tooth areas, it allows the lubricant agent to adhere
and dry. It also allows compounded molybdenum to form a disulfide metal
texture, to discourage corrosion.

WPC Treatment
WPC is a treatment, effective in encouraging fatigue
strength and reducing metal friction. This treatment helps
improve fatigue strength, but does not improve bending

Solid Lubrication Treatment

strength. Applied by spraying the gears in very small amounts,

40 to 200 m, at the speed of 100 m/sec or more. By using
this application, the process instantaneously generates heat
and melts the metallic crystal, creating a fine coating from
rapid cooling, Usually involves very little dimensional change;
expected change would be within 1 to 2 m.

WPC Treatment

- 31 -

The ABC's of GearsBasic Guide

9. Manufacturing of Gears
KHK stock gears are produced by the following
manufacturing processes.
For gear manufacturing, there are several fabrication approaches. However, we will
show you how KHK Stock Gears are produced by introducing our typical cutting
processes, selection of materials and the packaging of our gears.

9 1 Manufacturing Process of Spur Gears

Shown is a typical manufacturing process for the production of SS-type of KHK Spur Gears.
(Some photographs may not be of the SS-type of gears, and shown as examples)

Material Procurement

Rough Cutting

Lathe Operations

Source the material: S45C

Round Bars, KHK always
have plenty in stock.

Selection of material (round

bars). Diameter and length
are cut larger than the outer
diameter and length of the
finished product.

Perform rough machining to

create the basic form (gear
blank) by a lathe.

Black Oxide Coating

Burr Removal

Gear Cutting

Apply black oxide coating,

as a surface treatment, to
prevent rusting residue and
texturing.

Remove all imperfections

(burrs), chamfer the sharp
corners for safety in use
and to prevent fracturing.

Generate gear teeth by our

gear-cutting machines. After
cutting, gear teeth will have
imperfections.

Packing

Done!

and
duct
h pro
c
the
a
g
e
in
ge
l stat
Packa
e d la b e
t
n
ri
p
p la c e a name
t's
produc

- 32 -

9. Manufacturing of Gears

9 2 Manufacturing Process of Racks

Shown is a typical manufacturing process for the production of SRFD-type of KHK Racks.
(Some photographs may not be of the SRFD-type of gears, and shown as examples)

Material Procurement

Gear Cutting

Removal of Burrs

Source the material: S45C

Square Bars. KHK always
have plenty in stock.

Generate gear teeth by our

gear-cutting machines. After
cutting, gear teeth will have
imperfections.

Remove all imperfections

(burrs), chamfer the sharp
corners for safety in use
and to prevent fracturing.

Boring

End Machining

Press Operations

For mounting, boring of

counterbores is applied by
center machining.

For use of racks in contact,

end machining is applied
to align the ends, based on
tooth space.

Apply press operations

to correct warpage that
occurred in the gear-cutting
processes.

Packing

Black Oxide Coating

place a
uct and
d
ro
p
h
duct's
e eac
the pro
Packag
tating
s
l
e
b
la
printed
name

Apply black oxide coating,

as a surface treatment, to
prevent rusting residue and
texturing.

- 33 -

The ABC's of GearsBasic Guide

9 3 Manufacturing Process of Bevel Gears

This is a typical manufacturing process for SM-type of KHK Bevel Gears.

(Some photographs may not be of the SM-type of gears, and shown as examples)

Material Procurement

Rough Cutting

Lathe Operations

Source the material: S45C

Round bars, KHK always
have plenty in stock.

Selection of material (round bars).

Diameter and length are cut larger
than the outer diameter and length
of the finished product.

Machine to create basic

form (gear blank) by turning.

Black Oxide Coating

Burr Removal

Gear Cutting

Apply black oxide coating,

as a surface treatment, to
prevent rusting residue and
texturing.

Remove all imperfections

(burrs), chamfer the sharp
corners for safety in use and
to prevent fracturing.

Generate gear teeth by our

gear-cutting machines. After
cutting, gear teeth will have
imperfections.

Packing

Done!

nd
duct a
ch pro
he
t
a
e
g
in
e
t
g
bel sta
Packa
la
d
e
t
prin
place a
e
t's nam
c
u
d
ro
p

- 34 -

9. Manufacturing of Gears

9 4 Manufacturing Process of Worm Gears

This is a typical manufacturing process for SW-type of KHK Worm Gears.

(Some photographs may not be of the SW-type of gears, and shown as examples)

Material Procurement

Rough Cutting

Lathe Operations

Source the material: S45C

Round bars, KHK always
have plenty in stock.

Selection of material (round bars).

Diameter and length are cut larger
than the outer diameter and length
of the finished product.

Perform rough machining to

create the basic form (gear
blank) by turning.

Black Oxide Coating

Burr Removal

Gear Cutting

Apply black oxide coating,

as a surface treatment, to
prevent rusting residue and
texturing.

Remove all imperfections

(burrs), chamfer the sharp
corners for safety in use and
to prevent fracturing.

Generate gear teeth by

our gear-cutting machines.
After cutting, gear teeth
will have imperfections.

Packing

lace a
t and p
produc
h
duct's
c
a
ro
e
e
g the p
in
Packag
t
a
t
s
l
labe
printed
e
m
na

- 35 -

 All rights reserved herein and no portion of this booklet may be reproduced without the prior consent in
writing from KHK Co.,Ltd.
This booklet is published for the purpose of informing people about gears and is used as a KHK's sales
promotion advertisement.
No guarantee is given by KHK Co., Ltd. on the contents of these copyrighted works. Please note that,
even if there are any errors therein, we shall not be held responsible, whatsoever.
KHK Co., Ltd. reserves the right to make changes to the specifications and contents of this booklet,
without notice.

The ABC's of Gears

First Published: September 1, 2007
Copyright by Kohara Gear Industry Co., Ltd.
All rights reserved.
Publisher

Toshiharu Kohara

Published by

Kohara Gear Industry Co.,Ltd.

332-0022
1317

Editor / Producer Team: ABC's of Gears

Basic Guide - B

13-15 Nakacho, Kawaguchi-shi, Saitama-ken, 332-0022 JapanTEL:048-254-1744 FAX:048-254-1765

URL http://www.khkgears.co.jp/en/

E-mail export@khkgears.co.jp