T-62
Fig. 8-4 Spherical Basis of Octoid Bevel Crown Gear
8.2 Bevel Gear Tooth Proportions
Bevel gear teeth are proportioned in accordance with the standard system of tooth
proportions used for spur gears. However, the pressure angle of all standard design bevel
gears is limited to 20°. Pinions with a small number of teeth are enlarged automatically
when the design follows the Gleason system.
Since bevel-tooth elements are tapered, tooth dimensions and pitch diameter are
referenced to the outer end (heel). Since the narrow end of the teeth (toe) vanishes at the
pitch apex (center of reference generating sphere), there is a practical limit to the length
(face) of a bevel gear. The geometry and identification of bevel gear parts is given in
Figure 8-5.
8.3 Velocity Ratio
The velocity ratio (i ) can be derived from the ratio of several parameters:
z1 d1 sind1
i = –– = –– = –––––
(8-1)
z2 d2 sind2
where: d = pitch angle (see Figure 8-5, on following page)
8.4 Forms Of Bevel Teeth *
In the simplest design, the tooth elements are straight radial, converging at the cone
* The material in this section has been reprinted with the permission of McGraw Hill Book Co.,
Inc., New York, N.Y. from "Design of Bevel Gears" by W. Coleman, Gear Design and Applications, N.
Chironis, Editor, McGraw Hill, New York, N.Y. 1967, p. 57.
O
P
Great Circle
Tooth Profile
Line of Action
Pitch Line
