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.

—avoiding the sloppy aspect of light lining in drawings ;
and making the ink just so thick as to run freely from the
pen. This medium degree may be judged of after a little
practice by the appearance of the ink on the pallet. The
best quality of ink has a soft feel when wetted and
smoothed; free from grit or sediment, and musky. The
rubbinv of China ink in water tends to crack and break

O

away the surface at the point; this may be prevented by
shifting at intervals the position of the stick in the hand
while being rubbed, and thus rounding the surface. Nor
is it advisable, for the same reason, to bear very hard, as
the mixture is otherwise more evenly made, and the
enamel of the pallet is less rapidly worn off. When the
ink, on being rubbed down, is likely to be for some time
required, a considerable quantity of it should be prepared,
as the water continually vaporises: it will thus continue for
a longer time in a condition fit for application. The pen
should be levelled in the ink, to take up a sufficient charge;
and to induce the ink to enter the pen freely, the blades
should be lightly breathed upon before immersion. After
each application of ink, the outsides of the blades should be
cleaned, to prevent any deposit of ink upon the edge of
the squares.

To keep the blades of his inkers clean, is the first duty
of a draughtsman who is to make a good piece of work.
Pieces of blotting or unsized paper, and cotton velvet,

washleather, or even the sleeve of a coat, should always
be at hand while a drawing is being inked. When a small
piece of blotting paper is folded twice so as to present a
corner, it may usefully be passed between the blades of
the pen, now and then, as the ink is liable to deposit at
the point and obstruct the passage, particularly in fine-
lining ; and for this purpose the pen must be unscrewed to
admit the paper. But this process may be delayed by
drawing the point of the pen over a piece of velvet, or
even over the surface of thick blotting paper; either
method clears the point for a time. As soon as any
obstruction takes place, the pen should be immediately
cleaned, as the trouble thus taken will always improve
and expedite the work. If the pen should be laid down
for a short time with the ink in it, it should be unscrewed
to keep the points apart and so prevent deposit; and when
done with altogether for the occasion, it ought to be tho-
roughly cleaned at the nibs. This will preserve its edges
and prevent rusting.

For useful reference, to assist the judgment in the pre-
paration of drawings on paper, the drawing office should
be fitted with a vertical scale of full size feet and inches,
6 or 8 feet long, fixed against the wall; and with a hori-
zontal scale the full length of the office, fixed to the wall
at 7 or 8 feet above the floor. The scales should be painted
conspicuously in white, with black lining and figures.

PAET SECOND.

GEOMETRICAL CONST RUCTION S-D RAVIN G OP ELEMENTARY PORMS.

As Machinery is conceived and designed with the view
of doing work in the simplest way and by the most
direct means, its form and character are moulded largely
in conformity with geometrical or regular forms. Con-
structive geometry, indeed, lies at the foundation of the
whole, and the machinist should be qualified not only to
form just and clear conceptions of the nature and relation
geometrically of various parts in machinery, but also to
develope his conceptions in visible delineations,—in plainer
language, to be fit to make correct working drawings of
machinery on geometrical principles.

Definitions and Technicalities.

Geometry treats of the relations of lines, surfaces, and
solids; of which lines are measured by length simply,
having no breadth; surfaces, by length and breadth;
and solids, by length, breadth, and thickness or depth.

A point is a mere position, without magnitude ; as the
intersection of two lines, or the centre of a circle.

Lines may be straight or curved.

Surfaces may be flat or plane, or curved.

A plane is a perfectly flat surface.

Parallel lines are lines in the same plane, which are
equally distant from each other at every part; as, for
example, two opposite edges of a drawing-board.

Horizontal lines are such as are parallel to the horizon,
or level.

Vertical lines are such as are parallel to the position
at rest assumed by a plumb-line freely suspended in a still
atmosphere.

Inclined lines are such as are neither horizontal nor
vertical, and occupy intermediate positions. Also, two or
more lines which converge or run together, and which
would meet at a point, if produced far enough, are said to
be inclined to one another.

An angle is the divergence of two lines meeting or
cutting each other at a point. According to the amount
of divergence, the angle may be right, obtuse, or acute.

A right angle is formed by one straight line standing
on another {Fig. 31), so that the adjacent angles so formed
may be equal, each of these angles being a right angle;
and one line is said to be perpendicular to the other.
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