On the Economy of Machinery and Manufactures by Charles Babbage (english books to improve english TXT) 📕

to the calico. The substance of the cloth is pressed very

forcibly into the cavities thus formed, and retains its pattern

after considerable use. The watered appearance in the cover of

the volume in the reader’s hands is produced in a similar manner.

A cylinder of gun-metal, on which the design of the watering is

previously cut, is pressed by screws against another cylinder,

formed out of pieces of brown paper which have been strongly

compressed together and accurately turned. The two cylinders are

made to revolve rapidly, the paper one being slightly damped,

and, after a few minutes, it takes an impression from the upper

or metal one. The glazed calico is now passed between the

rollers, its glossy surface being in contact with the metal

cylinder, which is kept hot by a heated iron enclosed within it.

Calicoes are sometimes watered by placing two pieces on each

other in such a position that the longitudinal threads of the one

are at right angles to those of the other, and compressing them

in this state between flat rollers. The threads of the one piece

produce indentations in those of the other, but they are not so

deep as when produced by the former method.

122. Embossing upon leather. This art of copying from

patterns previously engraved on steel rollers is in most respects

similar to the preceding. The leather is forced into the

cavities, and the parts which are not opposite to any cavity are

powerfully condensed between the rollers.

123. Swaging. This is an art of copying practised by the

smith. In order to fashion his iron and steel into the various

forms demanded by his customers, he has small blocks of steel

into which are sunk cavities of different shapes; these are

called swages, and are generally in pairs. Thus if he wants a

round bolt, terminating in a cylindrical head of larger diameter,

and having one or more projecting rims, he uses a corresponding

swaging tool; and having heated the end of his iron rod, and

thickened it by striking the end in the direction of the axis

(which is technically called upsetting), he places its head upon

one part of the lage; and whilst an assistant holds the other

part on the top of the hot iron, he strikes it several times with

his hammer, occasionally turning the head one quarter round. The

heated iron is thus forced by the blows to assume the form of the

mould into which it is impressed.

124. Engraving by pressure. This is one of the most beautiful

examples of the art of copying carried to an almost unlimited

extent; and the delicacy with which it can be executed, and the

precision with which the finest traces of the graving tool can be

transferred from steel to copper, or even from hard steel to soft

steel, is most unexpected. We are indebted to Mr Perkins for most

of the contrivances which have brought this art at once almost to

perfection. An engraving is first made upon soft steel, which is

hardened by a peculiar process without in the least injuring its

delicacy. A cylinder of soft steel, pressed with great force

against the hardened steel engraving, is now made to roll very

slowly backward and forward over it, thus receiving the design,

but in relief. The cylinder is in its turn hardened without

injury., and if it be slowly rolled to and fro with strong

pressure on successive plates of copper, it will imprint on a

thousand of them a perfect facsimile of the original steel

engraving from which it was made. Thus the number of copies

producible from the same design may be multiplied a

thousand-fold. But even this is very far short of the limits to

which the process may be extended. The hardened steel roller,

bearing the design upon it in relief may be employed to make a

few of its first impressions upon plates of soft steel, and these

being hardened become the representatives of the original

engraving, and may in their turn be made the parents of other

rollers, each generating copperplates like their prototype. The

possible extent to which facsimiles of one original engraving may

thus be multiplied, almost confounds the imagination, and appears

to be for all practical purposes unlimited.

This beautiful art was first proposed by Mr Perkins for the

purpose of rendering the forgery of bank notes a matter of great

difficulty; and there are two principles which peculiarly adapt

it to that object: first, the perfect identity of all the

impressions, so that any variation in the minutest line would at

once cause detection; secondly, that the original plates may be

formed by the united labours of several artists most eminent in

their respective departments; for as only one original of each

design is necessary, the expense, even of the most elaborate

engraving, will be trifling, compared with the multitude of

copies produced from it.

125. It must, however, be admitted that the principle of

copying itself furnishes an expedient for imitating any engraving

or printed pattern, however complicated; and thus presents a

difficulty which none of the schemes devised for the prevention

of forgery appear to have yet effectually obviated. In attempting

to imitate the most perfect banknote, the first process would be

to place it with the printed side downwards upon a stone or other

substance, on which, by passing it through a rolling-press, it

might be firmly fixed. The next object would be to discover some

solvent which should dissolve the paper, but neither affect the

printing-ink, nor injure the stone or substance to which it is

attached. Water does not seem to do this effectually, and perhaps

weak alkaline or acid solutions would be tried. If, however, this

could be fully accomplished, and if the stone or other substance,

used to retain the impression, had those properties which enable

us to print from it, innumerable facsimiles of the note might

obviously be made, and the imitation would be complete. Porcelain

biscuit, which has recently been used with a black lead pencil

for memorandum books, seems in some measure adapted for such

trials, since its porosity may be diminished to any required

extent by regulating the dilution of the glazing.

126. Gold and silver moulding. Many of the mouldings used by

jewellers consist of thin slips of metal, which have received

their form by passing between steel rollers, on which the pattern

is embossed or engraved; thus taking a succession of copies of

the devices intended.

127. Ornamental papers. Sheets of paper coloured or covered

with gold or silver leaf, and embossed with various patterns, are

used for covering books, and for many ornamental purposes. The

figures upon these are produced by the same process, that of

passing the sheets of paper between engraved rollers.

Of copying by stamping

128. This mode of copying is extensively employed in the

arts. It is generally executed by means of large presses worked

with a screw and heavy flywheel. The materials on which the

copies are impressed are most frequently metals, and the process

is sometimes executed when they are hot, and in one case when the

metal is in a state between solidity and fluidity.

129. Coins and medals. The whole of the coins which circulate

as money are produced by this mode of copying. The screw presses

are either worked by manual labour, by water, or by steam power.

The mint which was sent a few years since to Calcutta was capable

of coining 200,000 pieces a day. Medals, which usually have their

figures in higher relief than coins, are produced by similar

means; but a single blow is rarely sufficient to bring them to

perfection, and the compression of the metal which arises from

the first blow renders it too hard to receive many subsequent

blows without injury to the die. It is therefore, after being

struck, removed to a furnace, in which it is carefully heated

red-hot and annealed, after which operation it is again placed

between the dies, and receives additional blows. For medals, on

which the figures are very prominent, these processes must be

repeated many times. One of the largest medals hitherto struck

underwent them nearly a hundred times before it was completed.

130. Ornaments for military accoutrements, and furniture.

These are usually of brass, and are stamped up out of solid or

sheet brass by placing it between dies, and allowing a heavy

weight to drop upon the upper die from a height of from five to

fifteen feet.

131. Buttons and nail heads. Buttons embossed with crests or

other devices are produced by the same means; and some of those

which are plain receive their hemispherical form from the dies in

which they are struck. The heads of several kinds of nails which

are portions of spheres, or polyhedrons, are also formed by these

means.

132. Of a process for copying, called in France clichee. This

curious method of copying by stamping is applied to medals, and

in some cases to forming stereotype plates. There exists a range

of temperature previous to the melting point of several of the

alloys of lead, tin, and antimony, in which the compound is

neither solid, nor yet fluid. In this kind of pasty state it is

placed in a box under a die, which descends upon it with

considerable force. The blow drives the metal into the finest

lines of the die, and the coldness of the latter immediately

solidifies the whole mass. A quantity of the half-melted metal is

scattered in all directions by the blow, and is retained by the

sides of the box in which the process is carried on. The work

thus produced is admirable for its sharpness, but has not the

finished form of a piece just leaving the coining-press: the

sides are ragged, and it must be trimmed, and its thickness

equalized in the lathe.

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