Gas Engine Magazine

Spherical Turning

By Staff

All tools for spherical or (as it is commonly termed)
‘ball’ turning operate on the same principle, which is that
of a cutter-head, tool rest, or equivalent appliance, whose
vertical axis is coincident with the axis of the ball or sphere to
be turned, or, what amounts to the same thing, with the axis of the
live-spindle of the lathe or machine, and which is capable of being
rotated on its pivot or axis in such manner that a tool fixed in
the cutter-head or tool rest, with its point or cutting edge
exactly on the same level as the lathe centers, will, when set at
any distance from the axis of the work, describe a true circle or
arc around the same, whose radius, when measured from the axis of
the work, will be the same at every point of its circumference,
thereby producing (when the tool is adjusted to the cut, and the
work is revolving in the ordinary way, and the cutter-head or tool
rest is rotated on its axis [pivot] as described) a true sphere
whose diameter measures the same at every point of its

In construction the rest consists of a base A, dove-tailed on
the bottom to fit into or over the cross-slide of the lathe
carriage, and bored at a to receive the pivot pin a of the tool
rest B which is slotted at b for the tool post C; the tool D can be
adjusted sufficiently for all practical purposes by means of the
adjusting screw E and set screw E the body of the rest is drilled
at c for the insertion of the lever F, by means of which the tool
rest and tool are rotated (fed) around the work as it revolves in
the lathe or machine.

On smaller lathes the base A is fitted directly on the lathe
bed, which can also be done on the larger lathes when desired.

The tool rest B can be fitted with a slide for adjusting the
tool in place of the slot b, if preferred.

For turning brass and other soft metal balls of small diameter
the above is an excellent appliance ; but for iron or steel balls
of any diameter a revolving sliding tool rest should be

A base plate (not shown) is fitted onto the cross-slide ways of
the lathe carriage, then upon this base plate is fitted the base A
(of the tool rest B) which is circular in form, and is geared at C
to engage with the worm D. The worm shaft F is journaled on the
lathe carriage in the brackets a a’, and on the lathe bed in
the bracket a’, and is actuated from the screw-cutting gears G.
The method of operating is so clearly shown in the engraving that
further explanation is thought to be unnecessary, except to touch
upon the two most important points, viz.: First, the imperative
necessity of having the vertical axis of the work and the pivot pin
of the tool rest coincident, and, secondly, of having the point or
cutting edge of the tool exactly level with the horizontal axes of
the lathe spindle and work.

If there is any divergence from a true coincidence in either
case, the ball would not be turned a true sphere, but would be oval
to just twice the extent that the tool rest, or tool point, are out
of a, true alignment.

  • Published on Sep 1, 1988
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