Chains and Gears 197
dharm
d:\N-Design\Des13-1.pm5
Shaft dia
a
d
Pitch cone
radius
a
B
Tw
L Hubdia
D
Tr
Pitch line
Fig. 13.12 Bevel gear
13.11.6 Bevel Gearing
Two bevel gears in mesh is known as bevel gearing. In bevel gearing, the pitch cone angles of
the pinion and gear are to be determined from the shaft angle, i.e., the angle between the
intersecting shafts. Figure 13.13 shows two views of a bevel gearing.
a
d
D
1
L 1
D 2
L^2
a
d
Pitch coneradius
B
a 1
a 2
B
Hubdia
Shaft
dia
Hub
dia
Fig. 13.13 Bevel gearing
13.11.7 Worm and Worm Gear (Wheel)
Worm and worm gear in combination, i.e., in meshing is known as worm gearing and is used in
speed reducers requiring large reductions. In worm gearing, the driving member is the worm,
which is in the form of a screw, having trapezoidal thread. The worm may have single or
multiple start threads which are left or right hand in nature. The driven member is known as
the worm gear or worm wheel. In one of the designs, the worm gear is in the form of a helical
gear, with teeth cut on a concave shaped periphery and thus enveloping the worm. Figure
13.14 shows the worm and worm gear indicated separately and Fig. 13.15, the same in mesh.
