Machinery Repairman

Figure 7-43.—Sprocket wheel cutter.
SPROCKET WHEEL CUTTER. —The
sprocket wheel cutter (fig. 7-43) is a formed cutter
that is used to mill teeth on sprocket wheels.
GEAR HOB.—The gear hob (fig. 7-44) is a
formed milling cutter with teeth cut like threads on a
screw.
FLY CUTTER.—The fly cutter (fig. 7-45) is
often manufactured locally. It is a single-point cutting
tool similar in shape to a lathe or shaper tool. It is
held and rotated by a fly cutter arbor. There will be
times when you need a special formed cutter for a
very limited number of cutting or boring operations.
This will probably be the type of cutter you will use
since you can grind it to almost any form you need.
We have discussed a number of the more common
types of milling machine cutters. For a more detailed
discussion of these, other types, and their uses,
consult the Machinery’s Handbook, machinist
publications, or the applicable technical manual. We
will now discuss the selection of cutters.
Figure 7-44.—Gear hob.
7-26
Selection
Figure 7-45.—Fly cutter arbor and fly cutters.
Each cutter can do one kind of job better than any
other cutter in a given situation. A cutter may or may
not be limited to a specific milling operation. To
select the most suitable cutter for a particular
operation, you must consider the kind of cut to be
made, the material to be cut, the number of parts to be
machined, and the type of milling machine available.
Another factor that affects a milling operation is
the number of teeth in the cutter. If there are too many
teeth, the space between them is so small that it
prevents the free flow of chips. The chip space
should also be smooth and free of sharp corners to
prevent the chips from clogging the space. A
coarse-tooth cutter is more satisfactory for milling
material that produces a continuous and curled chip.
The coarse teeth not only permit an easier flow of
chips and coolant but also help to eliminate chatter. A
fine-tooth cutter is more satisfactory for milling a thin
material. It reduces cutter and workpiece vibration
and the tendency for the cutter teeth to “straddle” the
work and dig in.
Another factor you should consider in selecting a
cutter is its diameter. Select the smallest diameter
cutter that will allow the arbor to pass over the work
without interference when you take the cut. Figure 7-46
shows that a small cutter takes a cut in less time than
a larger cutter.