T-34
SECTION 4 SPUR GEAR CALCULATIONS
4.1 Standard Spur Gear
Figure 4-1 shows the meshing of standard spur gears. The meshing of standard spur gears
means pitch circles of two gears contact and roll with each other. The calculation formulas are in
Table 4-1.
Fig. 4-1 The Meshing of Standard Spur Gears
(a = 20°, z1 = 12, z2 = 24, x1 = x2 = 0)
Table 4-1 The Calculation of Standard Spur Gears
* The subscripts 1 and 2 of z1 and z2 denote pinion and gear.
All calculated values in Table 4-1 are based upon given module (m) and number of teeth
(z1 and z2). If instead module (m), center distance (a) and speed ratio (i) are given, then the
number of teeth, z1 and z2, would be calculated with the formulas as shown in Table 4-2.
1
2
3
4
5
6
7
8
9
10
Module
Pressure Angle
Number of Teeth
Center Distance
Pitch Diameter
Base Diameter
Addendum
Dedendum
Outside Diameter
Root Diameter
m
a
z1, z2 *
a
d
db
ha
hf
da
df
3
20°
12
24
54.000
36.000
72.000
33.829
67.658
3.000
3.750
42.000
78.000
28.500
64.500
(z1 + z2)m *
––––––––––
2
zm
d cosa
1.00m
1.25m
d + 2m
d – 2.5m
No.
Item
Symbol
Formula
Example
Pinion
Gear
a
da2
d2
db2
df2
d1d
b1
a
a
O1
O2
