ry support for parts that are bored and therefore
cannot be centered.

[Illustration: Fig. 14. Bushing mounted on Arbor for Turning]

Another example of work that would be turned on an arbor is shown in
Fig. 15. This is a small cast-iron wheel having a finished hole through
the hub, and the outer surface and sides of the rim are to be turned
true with this hole. In this case, the casting would also be held by
pressing a mandrel through the hub; as shown. This method, however,
would only apply to comparatively small wheels because it would be
difficult, if not impossible, to prevent a large wheel from turning on
the arbor when taking a cut, and even if it could be driven, large work
could be done to better advantage on another type of machine. (The
vertical boring mill is used extensively for turning large wheels, as
explained in Chapter VI.) When turning the outside of the rim, a tool
similar to that shown at _t_ should be used, but for facing or turning
the sides, it might be better, if not necessary, to use tools having
bent ends as shown by the dotted lines; in fact, turning tools of
various kinds are made with the ends bent to the right or left, as this
enables them to be used on surfaces that could not be reached very well
with a straight tool. If a comparatively large pulley is mounted near
the end of the arbor, it can be driven directly by pins attached to the
faceplate and engaging the pulley arms. This method of driving is often
employed when the diameter to be turned is large and the hole for the
arbor is so small that there will not be sufficient friction for
driving.

[Illustration: Fig. 15. Turning Pulley Held on an Arbor]

=Different Types of Lathe Arbors.=--Three different types of lathe
arbors are shown in Fig. 16. The kind shown at _A_ is usually made of
tool steel and the body is finished to a standard size. The ends are
somewhat reduced and flat spots are milled, as shown, to give the
clamping screw of the dog a good grip. The body of the arbor is usually
tapered about 0.006 inch per foot. This taper makes it easier to insert
the arbor in a close-fitting hole, and it also permits slight variations
in the diameter of different holes. As to hardening, the practice at the
present time among manufacturers is to harden arbors all over, but for
extremely accurate work, an arbor having hardened ends and a soft body
is generally considered superior, as there is less tendency of
distortion from internal st