h other.

Sec. 56. It is not very easy for a beginner to turn a bit of
anything--iron, wood, or glass--with great accuracy to fit a template,
and consequently time may be saved by the following procedure, applied as
soon as the figure of the template is roughly obtained. A disc of
lead or iron, of the same diameter as the glass, and of approximately
the proper curvature, is prepared by turning, and is armed with a
handle projecting coaxially from the back of the disc. The glass
revolving with moderate speed on the lathe, the lead tool, supplied
with coarse emery and water, is held against it, care being taken to
rotate the tool by the handle, and also to move it backwards and
forwards across the disc, through a distance, say, up to half an inch;
if it is allowed to overhang too much the edges of the glass disc will
be overground. By the use of such a tool the glass can readily be
brought up to the template.

The only thing that remains, so far as the description of this part of
the process goes, is to give a note or two as to the best way of
making the lead tools, and for this purpose the main narrative of
processes must be interrupted. The easiest way is to make a set of
discs to begin with. For this purpose take the mandrel out of the
lathe, and place it nose downwards in the centre of an iron ring of
proper diameter on a flat and level iron plate.

The discs are made by pouring lead round the screw-nose of the
mandrel. This method, of course, leaves them with a hole in the
centre; but this can be stopped up by placing the hot disc (from
which the mandrel has been unscrewed) on a hot plate, and pouring in a
sufficiency of very hot lead; or, better still, the mandrel can be
supported vertically at any desired distance above the plate while the
casting is being poured. Lead discs prepared in this way are easily
turned so as to form very convenient chucks for brass work, and for
use in the case now being treated, they are easily turned to a
template, using woodturners' tools, which work better if oiled, and
must be set to cut, not scrape.

If the operator does not mind the trouble of cutting a screw, or if he
has a jaw chuck, the lead may be replaced by iron with some advantage.

The following is a neat way of making concave tools. It is an
application of the principle of having the cutting tool as long as the
radius of curvature, and allowing it to move about the centre of
curvature. Place the disc of i