resses. Hardened arbors are "seasoned" before
finish-grinding to relieve these internal stresses.

The solid type _A_, Fig. 16, is used very extensively, but in shops
where a great variety of work is being done and there are many odd-sized
holes, some form of expanding arbor _B_ can be used to advantage. This
type, instead of being solid, consists of a tapering inner arbor _M_ on
which is placed a split bushing that can be expanded, within certain
limits, by driving in the tapering member. The advantage of this type is
that a comparatively small stock of arbors is required, as
different-sized bushings can be used. This type can also be fitted to
holes of odd sizes, whereas a solid arbor must be provided for each
different size hole, unless the variation is very slight. The latter
are, however, more accurate than the expanding type.

[Illustration: Fig. 16. Different Types of Lathe Arbors]

Another form of expanding arbor is shown at _C_. This type has a
straight body _N_ in which four tapering grooves are cut lengthwise, as
shown, and there is a sleeve _S_, containing four slots that are located
to correspond with the tapering grooves. Strips s are fitted into these
slots, and as the part _N_ is driven in, the strips are moved outward as
they ascend the tapering grooves. By having different sets of these
strips of various heights, one arbor of this type can be made to cover
quite a range of sizes. It is not suited, however, to thin work, as the
pressure, being concentrated in four places, would spring a flexible
part out of shape.

The cone arbor or mandrel shown at _A_, in Fig. 17, is convenient for
holding parts having comparatively large holes, as it can be adjusted
for quite a range of diameters. The work is gripped between the two
cones _c_ and _c_{1}_ which are forced together by nut _n_. The cones
are prevented from turning upon the arbor by keys. This style of arbor
should not be used for accurate work. The threaded arbor _B_ is used for
facing the sides of nuts square with the tapped hole. When a nut is
first put upon the arbor, the rough side comes against an equalizing
washer _w_. This washer rests against a spherical seat so that it can
shift to provide a uniform bearing for the rough side of the nut, even
though it is not square with the tapped hole. This feature prevents the
nut from being canted on the arbor and insures an accurately faced nut.
The revolving conical center shown at _C_ is often used fo