similar, in many
respects, to those used in a lathe, although the shanks of the former
are shorter and more stocky than those of lathe tools. The cutting edges
of some of the tools also differ somewhat in form, but the principles
which govern the grinding of lathe and boring mill tools are identical,
and those who are not familiar with tool grinding are referred to
Chapter II, in which this subject is treated.

=Turning a Flywheel on a Vertical Mill.=--The turning of a flywheel is a
good example of the kind of work for which a vertical boring mill is
adapted. A flywheel should preferably be machined on a double-head mill
so that one side and the periphery of the rim can be turned at the same
time. A common method of holding a flywheel is shown in Fig. 9. The rim
is gripped by four chuck jaws _D_ which, if practicable, should be on
the inside where they will not interfere with the movement of the tool.
Two of the jaws, in this case, are set against the spokes on opposite
sides of the wheel, to act as drivers and prevent any backward shifting
of work when a heavy cut is being taken. The illustration shows the tool
to the right rough turning the side of the rim, while the left-hand tool
turns the periphery. Finishing cuts are also taken over the rim, at this
setting, and the hub is turned on the outside, faced on top, and the
hole bored.

[Illustration: Fig. 9. Turning the Rim of a Flywheel]

The three tools _A_, _B_ and _C_, for finishing the hole, are mounted in
the turret. Bar _A_, which carries a cutter at its end, first rough
bores the hole. The sizing cutter _B_ is then used to straighten it
before inserting the finishing reamer _C_. Fig. 10 shows the turret
moved over to a central position and the sizing cutter _B_ set for
boring. The head is centrally located (on this particular machine) by a
positive center-stop. The turret is indexed for bringing the different
tools into the working position, by loosening the clamping lever _L_ and
pulling down lever _I_ which disengages the turret lock-pin. When all
the flywheels in a lot have been machined as described, the opposite
side is finished.

[Illustration: Fig. 10. Tool B set for Boring the Hub]

[Illustration: Fig. 11. Diagrams showing Method of Turning and Boring a
Flywheel on a Double-head Mill having one Turret Head]

In order to show more clearly the method of handling work of this class,
the machining of a flywheel will be explained more in detail in
conn