Of Copying By Punching
133. This mode of copying consists in driving a steel punch
through the substance to be cut, either by a blow or by pressure.
In some cases the object is to copy the aperture, and the
substance separated from the plate is rejected; in other cases
the small pieces cut out are the objects of the workman's labour.
134. Punching iron plate for boilers. The steel punch used
for this purpose is from three-eighths to three-quarters of an
inch in diameter, and drives out a circular disk from a plate of
iron from one-quarter to five eighths of an inch thick.
135. Punching tinned iron. The ornamental patterns of open
work which decorate the tinned and japanned wares in general use,
are rarely punched by the workman who makes them. In London the
art of punching out these patterns in screw-presses is carried on
as a separate trade; and large quantities of sheet tin are thus
perforated for cullenders, wine-strainers, borders of waiters,
and other similar purposes. The perfection and the precision to
which the art has been carried are remarkable. Sheets of copper,
too, are punched with small holes about the hundredth of an inch
in diameter, in such multitudes that more of the sheet metal is
removed than remains behind; and plates of tin have been
perforated with above three thousand holes in each square inch.
136. The inlaid plates of brass and rosewood, called buhl
work, which ornament our furniture, are, in some instances,
formed by punching; but in this case, both the parts cut out, and
those which remain, are in many cases employed. In the remaining
illustrations of the art of copying by punching, the part made
use of is that which is punched out.
137. Cards for guns. The substitution of a circular disk of
thin card instead of paper, for retaining in its place the charge
of a fowling-piece, is attended with considerable advantage. It
would, however, be of little avail, unless an easy method was
contrived of producing an unlimited number of cards, each exactly
fitting the bore of the barrel. The small steel tool used for
this purpose cuts out innumerable circles similar to its cutting
end, each of which precisely fills the barrel for which it was
138. Ornaments of gilt paper. The golden stars, leaves, and
other devices, sold in shops for the purpose of ornamenting
articles made of paper and pasteboard, and other fancy works, are
cut by punches of various forms out of sheets of gilt paper.
139. Steel chains. The chain used in connecting the
mainspring and fusee in watches and clocks, is composed of small
pieces of sheet steel, and it is of great importance that each of
these pieces should be of exactly the same size. The links are of
two sorts; one of them consisting of a single oblong piece of
steel with two holes in it, and the other formed by connecting
two of the same pieces of steel, placed parallel to each other,
and at a small distance apart, by two rivets. The two kinds of
links occur alternately in the chain: each end of the single
pieces being placed between the ends of two others, and connected
with them by a rivet passing through all three. If the rivet
holes in the pieces for the double links are not precisely at
equal distances, the chain will not be straight, and will,
consequently, be unfit for its purpose.
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