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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THE

ENGINEER AND MACHINIST’S

DRAWING-BOOK.


PART FIRST.

CONSTRUCTION AND USE OE DRAWING INSTRUMENTS.

A WORK which proposes to enter thoroughly into the prin-
ciples and practice of Mechanical Drawing, is properly
introduced by a description of the instruments provided
for the use of the draughtsman, and an explanation of
their construction and various application. The elements
of this department of Drawing, consist of geometrical
figures delineated with as close an approximation as pos-
sible to mathematical truth; and they therefore require
the aid of mechanical contrivances to correct the less exact
operations of the unassisted eye and hand. The intelligent
and ingenious mechanician not unfrequently devises for
himself an instrument that works with all the truth of the
one contained in his mathematical case, and with greater
facility; and, indeed, many technical aids are constantly
used in the workshop, which, whilst they have identity of
principle with the compasses, protractor, parallel ruler,
&c,, admit of less formal and more rapid application to,
the draughtsman’s purposes. Moreover, the engineer has
frequently to construct drawings of a size far beyond the
capabilities of his case of instruments; and is thus com-
pelled, not more by the desire of saving time than by
absolute necessity, to tax his ingenuity in the contrivance
of aids equally true, but of longer range. These very facts
however, are the strongest arguments that can be adduced
for the necessity of grounding the young mechanician in
a knowledge of the construction and use of the commonly
received drawing instruments , since, just in the same
way as a boy acquires an acquaintance with arithmetic
through the formal rules of the schools, and. in after life,
works his business calculations by equally sure yet shorter
processes ; so the young mechanical draughtsman gathers,
from a thorough knowledge of his drawing-case, those fixed
and permanent principles of mathematical relation and
geometrical construction, which alone enable him to pro-
duce more simple and effective instruments for the daily
operations of the workshop. Whilst, therefore, we shall
notice some of the aids peculiar to the mechanical draughts-

man, it will be our chief anxiety to give all needful infor-
mation concerning those instruments which are in ordinary
and general use.

The contents of the Drawing-Case may be divided into
Compasses of various sorts—Single and Double Scales,
Protractors, Parallel Rulers, and Drawing Pens. Of each
of these we shall speak in order.

Compasses.

A pair of Compasses is an instrument too well known
to need a lengthened description. It consists of two legs,
jointed at one end, and opening freely to any extent that
falls within its range. Its use is, speaking in general, to
describe circles, or circular lines, and to measure off dis-
tances. Compasses are, however, of different kinds, and
the Drawing-Case usually includes Dividers, Compasses
with movable legs, Bow Compasses and Directors; and
to these may be added Proportional Compasses, and Beam
Compasses.

Dividers —These compasses are used for taking off
measurements from the scales, and transferring them to
the lines of any figure or drawing in course of construction.
They are also employed in bringing the dimensions of
any finished drawing or figure to its scale of construction.
Generally, they are applied to the measurement and com-
parison of distances. The common dividers are moderately-
sized compasses, without movable legs working somewhat
stiffly in the joint, and having fine, well-tempered points
of equal length, lying fairly upon each other when closed.
When dimensions are to be taken with extreme accuracy,
these dividers will not, under the most skilful manipu-
lation, work with the delicacy and certainty that are
required. In such cases, the draughtsman resorts to his
Hair Dividers : these are compasses in which one leg is
acted upon by a spring; and a finely-threaded screw,
pressing upon this spring, changes the direction of the

point to the nicety of a hair s-breadth. The distance to

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