directions simultaneously. In the case of an ordinary spherical
object, such as brass clack ball, the casting is made from a perfect
pattern having two small caps or shanks, in which the centers are also
marked to avoid centering by hand. It is fixed in the machine between
two centers carried on a face plate or chuck, with which they revolve.
One of these centers, when the machine is in motion, receives a
continuous rotary motion about its axis from a wormwheel, D. This is
driven by a worm, C, carried on a shaft at the back of the chuck, and
driven itself by a wormwheel, B, which gears with a screw which rides
loosely upon the mandrel, and is kept from rotating by a finger on the
headstock. This center, in its rotation, carries with it the ball,
which is thus slowly moved round an axis parallel to the face plate,
at the same time that it revolves about the axis of the mandrel, the
result being that the tool cuts upon the ball a scroll, of which each
convolution is approximately a circle, and lies in a plane parallel to
the line of centers.

When the chuck is set for one size of ball, which may be done in a few
minutes, any quantity of that diameter may be turned without further
adjustment. A roughing cut for a 2 in. ball may be done in one minute,
and a finishing cut leaving the ball quite bright in the same time.
The two paps are cut off within one-sixteenth of an inch and then
broken off, and the ball finished in the usual way. On account of the
work being geometrically true, the finishing by the ferrule tool is
done in one quarter of the time usually required.

[Illustration: IMPROVED BALL TURNING MACHINE.]

The chuck may be applied to an ordinary lathe or may be combined with
a special machine tool, as show in our illustration. In the latter