Figure 7-43.--Sprocket wheel cutter.
SPROCKET WHEEL CUTTER. --The
sprocket wheel cutter (fig. 7-43) is a formed cutter
Figure 7-45.--Fly cutter arbor and fly cutters.
that is used to mill teeth on sprocket wheels.
GEAR HOB.--The gear hob (fig. 7-44) is a
Selection
formed milling cutter with teeth cut like threads on a
screw.
Each cutter can do one kind of job better than any
other cutter in a given situation. A cutter may or may
FLY CUTTER.--The fly cutter (fig. 7-45) is
not be limited to a specific milling operation. To
often manufactured locally. It is a single-point cutting
select the most suitable cutter for a particular
tool similar in shape to a lathe or shaper tool. It is
operation, you must consider the kind of cut to be
held and rotated by a fly cutter arbor. There will be
made, the material to be cut, the number of parts to be
times when you need a special formed cutter for a
machined, and the type of milling machine available.
very limited number of cutting or boring operations.
This will probably be the type of cutter you will use
Another factor that affects a milling operation is
since you can grind it to almost any form you need.
the number of teeth in the cutter. If there are too many
We have discussed a number of the more common
teeth, the space between them is so small that it
types of milling machine cutters. For a more detailed
prevents the free flow of chips. The chip space
discussion of these, other types, and their uses,
should also be smooth and free of sharp corners to
consult the Machinery's Handbook, machinist
prevent the chips from clogging the space. A
publications, or the applicable technical manual. We
coarse-tooth cutter is more satisfactory for milling
will now discuss the selection of cutters.
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
Figure 7-44.--Gear hob.
a larger cutter.
7-26