1.4 Terminology of each part of the gear
Terminologies of gears are defined in JIS B 0102:1999 Vocabulary of gear terms-Related to geometry.
The vocabularies for gear numerical formula and gear drawings are defined in JIS B 0121:1999 International gear notation - Symbols for geometrical data.
Comparison table 2 for common gear terms of JIS B 0102:1993(old) and JIS B 0102:1999 are confirmed. The names
are changed but meanings are retained.
Table 2. Comparison between new and old for gear terms.
JIS B 0102:1999

JIS B 0102: 1993 confirmed

Reference circle (1)Reference pitch circle

Reference diameter

Reference pitch diameter

Tooth depth

Tooth depth

Tooth thickness

Circular tooth thickness

Working depthWorking depth

Standard basic rack

Basic Rack (2)Datum line of Rack

Pitch line for rack

Virtual cylindrical gear of Bevel gear

Virtual spur gear for Bevel gear

Pitch angle

Pitch angle

Tip angle

Tip cone angle

Root angle

Root angle

Spiral angle for Bevel gear

(Bevel gear) Spiral angle

Locating distance for Bevel gear

(Bevel gear) Location distanceCentre distance modification coefficient

Coefficient of increment Centre distance

Note (1)	Pitch diameter is stipulated in JIS B0102:1999. Reference circle is classified with Pitch circle. Pitch circle isdiameter of geometrical circle for gear described by moment of relative motion of axis with mating gear.
Note (2)	Definition of Basic rack is “imaginary rack with Standard basic rack” under the Normal section in JIS0102:1999
In addition, the gears terms have been updated but not outlined.
Standard basic rack tooth profile
Rack tooth profile is stipulated in JIS B 0102:1999, Standard tooth profile dimension in Involute tooth profile group.
Therefore the gear and dimensions of tool are established while compatibility is kept.
The details of Standard basic rack tooth profile are shown in Fig. 5 and Table 3. According to the JIS B1701-1:1999 Involute tooth profile Article 1: Standard basic rack tooth profile and it’s recommended attached supplement articles
adds Tooth profile and Usage of Basic rack for reference, which is ommitted here.
Table 3. Dimensions of Standard basic rack
p=πm
Sp

Ap

ep

Tooth Tip

hpw

P

Vocabulary

Dimension of Standard basic rack

αp20°

hap

1.00mm

Cp

0.25m

hfp

1.25m

Pfp

0.38m

cp

Pfp

hFfp

hfp

hp

hap

Standard basic rack
tooth profile

cp

Mating of Standard basic
rack tooth profile

Tooth Root
Fig. 5 S tandard basic rack tooth profile and Mating of Standard basic rack tooth profile11

Gear terms and Vocabularies for Involute gear

(JIS B 0102:1993 confirmed and extracted from JIS B 0121:1999)
Fig. 6 indicates the names (gear terms) for parts of Tooth profile.
Standard is a defined term of an applicable limited word from Reference surface of gear, defined in JIS B 0102:1999.
Normally “Standard” and “Working” are distinguished. When it is not necessary to classify between Standard andWorking, it is common knowledge that the word “Standard” can be omitted.
Centre distance is defined as the shortest distance between axes of Parallel gear pair or pairof crossed gear.
Reference centre distance is defined in JIS B 0121:1999 which is not outlined here.
Circular pitch∗ ― p
Circular pitch is the distance of Pitch between adjacent teeth as measured on the Reference
circle or Reference line.
∗Base pitch ― pb
Base pitch is perpendicular line to Pitch between any section of Tooth profile in Involute gear.
Tooth depth ― hTooth depth is radial distance between Tip and Root circle.
Addendum ― ha
Addendum is radial distance between Tip and Reference circle.
Dedendum ― hf
Dedendum is radial distance between Root and Reference circle.
Working depth ― h’. Working depth is distance along the centre line between Tip surface of two engaging gears.
Bottom clearance ― c Bottom clearance is distance along the centre line between Tip surface of a Gear and Rootsurface of its Mating gear.
Tooth thickness ― s. This is length of Arc on Reference circle between the two profiles of a tooth.
Tip diameter ― daThis is diameter of Tip circle.
Reference diameter ― d. This is diameter of Reference circle.
Root diameter ― df.
This is diameter of Root circle.
Transverse line of action This is normal line common to two Transverse profiles at their point of contact. For Involutegear pairs, the lines of action are also common tangents to their Base circles.
Pressure angle ―α .
Angle drawn when centre connection line and profile crosses pitch point upon the referencecircle.
Centre distance―aThe term of ∗-mark is not define in JIS B 0121:1999. The Pressure angle is supplemented due to insufficient description in this JIS. An Addendum and Dedendum of Worm wheel is defined for classification of ‘’ Reference’’ and ‘’ Mating’’, which omitted here.
a = Centre distance c = Bottom clearance
p = Circular pitchs = Tooth thickness
pb = Base pitchda = Tip (Out side) diameter
h = Tooth depth
d = Reference diameter
ha = Addendum
db = Base diameter
hf = Dedendum
df = Root diameterh’ = Working depth α = Pressure angleFig. 6 Name of the each parts of Tooth profileAdaddbdf

Line of actionshf

chapb

hphʼa12