rk is shown in Fig. 43. This is a
rectangular-shaped casting having a round boss or projection, the end
_e_ of which is to be turned parallel with the back face of the casting
previously finished on a planer. A rough cored hole through the center
of the boss also needs to be bored true.

The best way to perform this operation in the lathe would be to clamp
the finished surface of the casting directly against the faceplate by
bolts and clamps _a_, _b_, _c_, and _d_, as shown; the work would then
be turned just as though it were held in a chuck. By holding the casting
in this way, face _e_ will be finished parallel with the back surface
because the latter is clamped directly against the true-running surface
of the faceplate. If a casting of this shape were small enough it could
also be held in the jaws of an independent chuck, but if the surface e
needs to be exactly parallel with the back face, it is better to clamp
the work to the faceplate. Most lathes have two faceplates: One of small
diameter used principally for driving work turned between centers, and a
large one for holding heavy or irregularly shaped pieces; either of
these can be screwed onto the spindle, and the large faceplate has a
number of slots through which clamping bolts can be inserted.

[Illustration: Fig. 43. Casting Clamped to Faceplate for Turning and
Boring]

The proper way to clamp a piece to the faceplate depends, of course,
largely on its shape and the location of the surface to be machined, but
in any case it is necessary to hold it securely to prevent any shifting
after a cut is started. Sometimes castings can be held by inserting
bolts through previously drilled holes, but when clamps are used in
connection with the bolts, their outer ends are supported by hardwood or
metal blocks which should be just high enough to make the clamp bear
evenly on the work. When deep roughing cuts have to be taken,
especially on large diameters, it is well to bolt a piece to the
faceplate and against one side of the casting, as at _D_, to act as a
driver and prevent the work from shifting; but a driver would not be
needed in this particular case. Of course a faceplate driver is always
placed to the rear, as determined by the direction of rotation, because
the work tends to shift backward when a cut is being taken. If the
surface which is clamped against the faceplate is finished as in this
case, the work will be less likely to shift if a piece of paper is
pl