ω
=
W
t
v
t
Knowing how the power splits enables the determination of
the transmitted load at each mesh.
(
a
)
Form milling cutter
(
b
) Spur gear shaper cutter
(
c
) Hob for small pitch gears having large teeth
(
d
) Hob for high pitch gears having small teeth
FIGURE 9–4
A variety of gear cutting tools
(Gleason Cutting Tools Corporation, Loves Park, IL)
CHAPTER NINE
Spur Gear Design
325
(
a
)
Gear being shaped with shaping cutter
FIGURE 9–5
Gear shaping operation and shaping machine
(Bourn & Koch, Inc., Rockford, IL USA)
(
b
)
Gear shaping machine
of the next adjacent space. This method is used mostly for
large gears, and great care is required to achieve accurate
results.
Shaping
[Figures 9–4(b) and 9–5] is a process in which
the cutter reciprocates, usually on a vertical spindle. The
shaping cutter rotates as it reciprocates and is fed into the
gear blank. Thus, the involute-tooth form is generated grad-
ually. This process is frequently used for internal gears.
Hobbing
[Figures 9–4(c) and (d) and 9–6] is a process
similar to milling except that the workpiece (the gear blank)
and the cutter (the hob) rotate in a coordinated fashion. Here
also, the tooth form is generated gradually as the hob is fed
into the blank.
The gear teeth are finished to greater precision after
form milling, shaping, or hobbing by the processes of
grinding, shaving, and honing. Being products of sec-
ondary processes, they are expensive and should be used
only where the operation requires high accuracy in the
tooth form and spacing. Figure 9–7 shows a gear grinding
machine.
(
b
)
Large hobbing machine
(
a
) Long pinion and a hob in a hobbing machine
Pinion
Hob
FIGURE 9–6
Gear hobbing operation and hobbing machine
(Bourn & Koch, Inc., Rockford, IL USA)
