Copying With Elongation





140. In this species of copying there exists but little

resemblance between the copy and the original. It is the

cross-section only of the thing produced which is similar to the

tool through which it passes. When the substances to be operated

upon are hard, they must frequently pass in succession through

several holes, and it is in some cases necessary to anneal them

at intervals.



141. Wire drawing. The metal to be converted into wire is

made of a cylindrical form, and drawn forcibly through circular

holes in plates of steel: at each passage it becomes smaller.

and, when finished, its section at any point is a precise copy of

the last hole through which it passed. Upon the larger kinds of

wire, fine lines may sometimes be traced, running longitudinally.

these arise from slight imperfections in the holes of the

draw-plates. For many purposes of the arts, wire, the section of

which is square or half round, is required: the same method of

making it is pursued, except that the holes through which it is

drawn are in such cases themselves square, or half-round, or of

whatever other form the wire is required to be. A species of wire

is made, the section of which resembles a star with from six to

twelve rays; this is called pinion wire, and is used by the

clockmakers. They file away all the rays from a short piece,

except from about half an inch near one end: this becomes a

pinion for a clock; and the leaves or teeth are already burnished

and finished, from having passed through the draw-plate.



142. Tube drawing. The art of forming tubes of uniform

diameter is nearly similar in its mode of execution to wire

drawing. The sheet brass is bent round and soldered so as to form

a hollow cylinder; and if the diameter outside is that which is

required to be uniform, it is drawn through a succession of

holes, as in wire drawing: If the inside diameter is to be

uniform, a succession of steel cylinders, called triblets, are

drawn through the brass tube. In making tubes for telescopes, it

is necessary that both the inside and outside should be uniform.

A steel triblet, therefore, is first passed into the tube, which

is then drawn through a succession of holes, until the outside

diameter is reduced to the required size. The metal of which the

tube is formed is condensed between these holes and the steel

cylinder within; and when the latter is withdrawn the internal

surface appears polished. The brass tube is considerably extended

by this process, sometimes even to double its first length.



143. Leaden pipes. Leaden pipes for the conveyance of water

were formerly made by casting; but it has been found that they

can be made both cheaper and better by drawing them through holes

in the manner last described. A cylinder of lead, of five or six

inches in diameter and about two feet long, is cast with a small

hole through its axis, and an iron triblet of about fifteen feet

in length is forced into the hole. It is then drawn through a

series of holes, until the lead is extended upon the triblet from

one end to the other, and is of the proper thickness in

proportion to the size of the pipe.



144. Iron rolling. When cylinders of iron of greater

thickness than wire are required, they are formed by passing

wrought iron between rollers, each of which has sunk in it a

semi-cylindrical groove; and as such rollers rarely touch

accurately, a longitudinal line will usually be observed in the

cylinders so manufactured. Bar iron is thus shaped into all the

various forms of round, square, half-round, oval, etc. in which

it occurs in commerce. A particular species of moulding is thus

made, which resembles, in its section, that part of the frame of

a window which separates two adjacent panes of glass. Being much

stronger than wood, it can be considerably reduced in thickness,

and consequently offers less obstruction to the light; it is much

used for skylights.



145. It is sometimes required that the iron thus produced

should not be of uniform thickness throughout. This is the case

in bars for railroads, where greater depth is required towards

the middle of the rail which is at the greatest distance from the

supports. This form is produced by cutting the groove in the

rollers deeper at those parts where additional strength is

required, so that the hollow which surrounds the roller would, if

it could be unwound, be a mould of the shape the iron is intended

to fit.



146. Vermicelli. The various forms into which this paste is

made are given by forcing it through holes in tin plate. It

passes through them, and appears on the other side in long

strings. The cook makes use of the same method in preparing

butter and ornamental pastry for the table, and the confectioner

in forming cylindrical lozenges of various composition.





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