Armengaud, Jacques Eugène; Leblanc, César Nicolas   [Hrsg.]; Armengaud, Jacques Eugène   [Hrsg.]; Armengaud, Charles   [Hrsg.]
The engineer and machinist's drawing-book: a complete course of instruction for the practical engineer: comprising linear drawing - projections - eccentric curves - the various forms of gearing - reciprocating machinery - sketching and drawing from the machine - projection of shadows - tinting and colouring - and perspective. Illustrated by numerous engravings on wood and steel. Including select details, and complete machines. Forming a progressive series of lessons in drawing, and examples of approved construction — Glasgow, 1855

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CONSTRUCTION AND USE OF DRAWING INSTRUMENTS.

17

pencil; we prefer a sliarp knife. Amongst the minor
things requiring special attention, the cutting and point-
ing of pencils is one of some consequence, both in point of
economy and pleasant working. A carelessly cut pencil
is constantly requiring the knife; and at the same time it
works with much uncertainty along the straight edge of
the square.

Pins.

Pins for holding down sheets not fixed by glue or
otherwise, are convenient. These should be (Fig. m
made with a broad flat head, of brass, and
rounded so as to permit the squares to slide
easily over it and the stem, of steel, rivetted
into the head. (Fig. SO) shows a good form
of pin. The stem is in some cases screwed
in, but is then liable to wear loose; the taper
of the stem should be moderate, so as not to work out
when fixed into the board.

General Remarks on Drawing.—Management of the
Instruments.

In constructing preparatory pencil-drawings, it is advis-
able, as a rule of general application, to make no more
fines upon the paper than are necessary to the completion
of the drawing in ink; and also to make these fines just
so dark as is consistent with the distinctness of the work.
With respect to the first idea, it is of frequent application:
in the case, for example, of the teeth of spur wheels, where,
in many instances, all that is necessary to the drawing
of their end view in ink, are three circles, one of them
for the pitch fine, and the two others for the tops and
bottoms of the teeth; and again, to draw the face view
of the teeth, that is, in the edge view of the wheel, we
have only to mark off by dividers, the positions of the
fines which compose the teeth, and draw four pencil fines
for the two sides, and the top and bottom of the eleva-
tion. And here we may remark the inconvenience of that
arbitrary rule, by which it is by some insisted that the
pupil should lay down in pencil every fine that is to be
drawn, before finishing it in ink. It is often beneficial to
ink in one part of a drawing, before touching other parts
at all: it prevents confusion, makes the first part of easy
reference, and allows of its being better done, as the sur-
face of the paper inevitably contracts dust, and becomes
otherwise soiled in the course of time, and therefore the
sooner it is done with the better.

Circles and circular arcs should, in general, be inked in
before straight fines, as the latter may be more readily
drawn to join the former, than the former the latter.
When a number of circles are to be described from one
centre, the smaller should be inked first, while the centre
is in better condition. When a centre is required to bear
some fatigue, it should be protected with a thickness of stout
card glued or pasted over it, to receive the compassdeg.

Indiarubber is the ordinary medium for cleaning a
drawing, and for correcting errors in the pencil. For
slight work it is quite suitable; that substance, however,

operates to destroy the surface of the paper; and by re-
peated application, it so ruffles the surface, and imparts an
unctuosity to it, as to spoil it for fine drawing, especially
if ink-shading or colouring is to be applied. It is much
better to leave trivial errors alone, if corrections by the
pencil may be made alongside without confusion; as it is,
in such a case, time enough to clear away superfluous fines
when the inking is finished.

For cleaning a drawing, a piece of bread two days old is
preferable to indiarubber, as it cleans the surface well and
does not injure it. When ink fines to any considerable
extent, have to be erased, a small piece of damped soft
sponge may be rubbed over them till they disappear. As,
however, this process is apt to discolour the paper, the
sponge must be passed through clean water, and applied
again to take up the straggling ink. For ordinary, small
erasures of ink fines, a sharp rounded pen-blade applied
lightly and rapidly does well, and the surface may be
smoothed down by the thumb-nail. In ordinary working
drawings a fine may readily be taken out by damping it
with a hair pencil and quickly applying the indiarubber;
and, to smooth the surface so roughened, a fight applica-
tion of the knife is expedient. In drawings intended to be
highly finished, particular pains should be taken to avoid
the necessity for corrections, as everything of this kind
detracts from the appearance.

In using the square, the more convenient way is to
draw the fines off the left edge, with the right hand,
holding the stock steadily but not very tightly, against
the edge of the board with the left hand. The conveni-
ence of the left edge for drawing by, is obvious, as we are
able to use the arms more freely, and we see exactly what
we are doing.

To draw fines in ink with the least amount of trouble
to himself, the mechanical draughtsman ought to take the
greater amount of trouble with his tools. If they be well
made, and of good stuff originally, they ought to last
through three generations of draughtsmen ; their working
parts should be carefully preserved from injury, they
should be kept well set, and above all scrupulously clean.
The setting of instruments is a matter of some nicety, for
; which purpose a small oil-stone is convenient. To dress
up the tips of the blades of the pen, or of the bows, as they
are usually worn unequally by the customary usage, they
may be screwed up into contact, in the first place, and
passed along the stone, turning upon the point in a directly
perpendicular plane, till they acquire an identical profile.
Being next unscrewed, and examined to ascertain the
parts of unequal thickness round the nib, the blades are
laid separately upon their backs on the stone, and rubbed
down at the points, till they be brought up to an edge of
uniform fineness. It is well to screw them together again,
and to pass them over the stone once or twice more, to
bring up any fault; to retouch them also on the outer
and inner side of each blade, to remove barbs or frasing ;
and finally to draw them across the palm of the hand,

The China ink, which is commonly used for fine-draw-
ing, ought to be rubbed down in water to a certain degree:

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