in. in diameter, the
plate being 1 and one-eighth in. thick, is three hours. Of course, if
several boilers of one size are being made at the same time, the holes
in two or more of these plates can be cut out at once. The machine is of
such design that it can be placed with one of the horizontal bed-plates
(say A 1), parallel and close up to a wall of the boiler shop; and when
the turning apparatus is being used, the vertical arm B 2 can be
swiveled half way round on its square box E 2, and used for drilling and
tapping the stay holes in marine boiler ends after they are put
together; of course sufficient room must be left between bed-plate A 2,
and the wall of boiler shop parallel with it, to allow for reception of
the boiler to be operated upon.

It would obviously be quite difficult to draw such drawings as in
Figures 298 and 299 on thin paper, so as to enable the drawing to be
traced on the wax direct by the process before described, unless indeed
the draftsman had considerable experience in fine work; hence, it is not
uncommon to make the drawing large, and on ordinary drawing paper. The
engraver then has the drawing photographed on the surface of the wax,
and works to the photograph. The letters of reference in wax engravings
are put in by impressing type in the wax, and in this connection it may
be remarked that the letters I and O should not be used on drawings to
be engraved by the wax process, unless they are situated outside the
outlines of the drawing, because the I looks so much like part of a
dotted line that it is often indistinguishable therefrom, while the O
looks like a circle or an ellipse.

CHAPTER XIV.

_SHADING AND COLORING DRAWINGS._

The shading or coloring of drawings by tints is more employed in large
drawings than in small ones, and in Europe than in the United States;
while on the other hand tinting by means of line-shading is more
employed in the United States than in Europe, and more on small drawings
than on large ones.

Many draftsmen adopt the plan of coloring the journals of shafts, etc.,
with a light tint, giving them the deepest tint at the circumference to
give them a cylindrical appearance. This makes the drawing much clearer
and takes but little time to do, and is especially advantageous where
the parts are small or on a small scale, so that the lines are
comparatively close together.

For simple shading purposes black tints of various degrees of darkness
may be empl