tire rim; in other
words, the rim should be set concentric with the table, as shown in Fig.
3, and the sides of the rim should also be parallel to the table.

[Illustration: Fig. 3. Plan View showing Flywheel Casting Chucked for
Turning]

A simple tool that is very useful for testing the position of any
cylindrical casting consists of a wooden shank into which is inserted a
piece of wire, having one end bent. This tool is clamped in the toolpost
and as the work revolves the wire is adjusted close to the cylindrical
surface being tested. The movement of the work with relation to the
stationary wire point will, of course, show whether or not the part runs
true. The advantage of using a piece of wire for testing, instead of a
rigid tool, is that the wire, owing to its flexibility, will simply be
bent backward if it is moved too close to a surface which is
considerably out of true. The upper surface of a casting can be tested
for parallelism with the table by using this same wire gage, or by
comparing the surface, as the table is revolved slowly, with a tool held
in the toolpost. An ordinary surface gage is also used for this purpose.
The proper surface to set true, in any case, depends upon the
requirements. A plain cylindrical disk would be set so that the outside
ran true and the top surface was parallel with the table. When setting a
flywheel, if the inside of the rim is to remain rough, the casting
should be set by this surface rather than by the outside, so that the
rim, when finished, will be uniform in thickness.

As far as possible, chucks should be used for holding cylindrical parts,
owing to their convenience. The jaws should be set against an interior
cylindrical surface whenever this is feasible. To illustrate, the
flywheel in Fig. 3 is gripped by the inside of the rim which permits the
outside to be turned at this setting of the work. It is also advisable
to set a flywheel casting in the chuck so that a spoke rests against one
of the jaws as at _d_, if this is possible. This jaw will then act as a
driver and prevent the casting from slipping or turning in the chuck
jaws, owing to the tangential pressure of the turning tool. When a cut
is being taken, the table and work rotate as shown by arrow _a_, and the
thrust of the cut (taken by tool _t_) tends to move the wheel backward
against the direction of rotation, as shown by arrow _b_. If one of the
chuck jaws bears against one of the spokes, this movement is p