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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ENGINEER AND MACHINIST'S DRAWING-BOOK.

cular lines may be drawn by the upright edge. The most
convenient size for general use measures from to 4 inches
on the side. A larger size, 8 or 9 inches long on the side,
is convenient for use in making large scale drawings. Ap-
plying one or other edge of the triangle, b, to the square,
the slant side gives at once the boundaries of all hex-
agonal and triangular figures, as nuts and bolt-heads, and
also the centre-lines of wheels, &c., with six arms. This

triangle may be of two sizes, 5 inches high and upwards.
Of the two set-squares, the second is the more convenient
for general use in drawing perpendiculars, as it is larger
and has a shorter base, and is more easily handled. Still
sharper set-squares are sometimes used ; also compound
triangles, having the slant-edge broken into two lines of
different slopes. Neither of these is to be recommended.
Circular openings are sometimes made in the body of the
triangle for facility in handling; but they are of no
moment, indeed we prefer the solid triangle.

Triangles are further useful in connection with each
other, or with the straight edge, for drawing short parallels
and perpendiculars without the use of the T square as shall
be exemplified in the proper place.

Sweeps and Variable Curves.

For drawing circular arcs of large radius, beyond the
range of the ordinary compasses, thin slips of wood, termed

(.Fig. 270

sweeps, are usefully employed, of which one or both edges
are cut to the required circle. For curves which are not
circular, but variously elliptic or
otherwise, “ universal sweeps,"
made of thin wood, of variable
curvature, are very serviceable.

The two examples {Figs. 27, 28)
have been found from experi-
ence to meet almost all the One-fourth fmi size,

requirements of ordinary drawing practice. Whatever be
the nature of the curve, some portion of the universal
sweep will be found to coincide with its commencement,

and it can be continued throughout its extent by applying
successively such parts of the sweep as are suitable, taking
care, however, that the continuity is not injured by
unskilful junction.

Pencils.

Pencils are of various qualities, distinguished by letter-
marks. The H B (hard and black) quality is usually
recommended ; but it is too soft to retain long the firm
point usually required for the correct execution of mecha-
nical drawings; and, besides, the softer pencils are the
more unctuous, and therefore the less ready in taking on
ink lines than the harder. F pencils work pretty well
upon smooth paper; but for drawing paper of a thick
and rougher quality, especially after having been damp-
stretched, H IT, and still better IT H PI pencils (of
two or three degrees of hardness), are better suited to
retain their sharpness. They are further recommended
by the lightness and delicacy of the lines that may be
thrown off by them ; for when a pencil drawing is made
with the view of being done over with ink-lines, the
excellence of these lines, as well as the readiness with
which they are produced, depends much upon the quality
of the pencilling.

Pencil lines, intended to be made permanent in ink,
ought to be entered very delicately, and made just so
dark as to render them distinct, for the more lightly
they are executed, the fitter they are to receive the ink.
A little practice and a steady hand, will secure the end
proposed. The pencil need not be held tightly; a slight
hold, without slackness, is what is wanted, inclined a little
to the side toward which the line is drawn. Besides a
1 drawing pencil for straight lines, it is well to have one for
sketching in small circles, not requiring the regular appl i -
cation of the pencil bows, as the rounding and filling up
of corners, ends of bolts, and the like. The straight-line
pencil, to be properly cut for use, should in the first place
be cut down to the flat side of the lead, in a plane nearly
parallel to the axis; then cut away on the opposite side to
a bevel considerably inclined, and cut, likewise, trans-
versely, at equal angles. The lead being thus laid bare,
should be pared down gradually on the three inclined
sides, till brought to a fine edge viewed laterally, and a
flat round point in the other aspect, as in (Fig. 29). The
less inclined side, when applied to a square, admits of
the point being brought close to the
edge, by which the line is more
certainly drawn ; and the roundness
of the point keeps the pencil longer
in working order. The sharpen-
ing of a sketching pencil is simply
conical, and brings it to a fine point.
To produce a good working pencil,
a sharp knife is indispensable; if
the knife be blunt, the point will
invariably break away before it is
properly brought up—a very fine flat file, or a pumice-
stone, is sometimes used to bring up the point of the

(Fig. 28.)

(Fig. 29)
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