A practical self-instruction manual that guides readers through learning mechanical drawing for industrial use. It explains basic techniques — chalk-work, freehand sketching, instrumental drafting, geometric constructions, and perspective — and emphasizes drawing to scale and accuracy. Sections describe tools, instruments, board work, and step-by-step exercises, with advice on persistence, first principles, and when to seek hands-on help from experienced draughtsmen. The text also outlines the draughtsman’s roles in design and production, how to read drawings, and uses sketching for quick communication in workshops, aiming to equip learners with the skills to produce clear, functional technical illustrations.
Section-Lining.
Cross-hatching has been defined in the “preliminary
definitions” to drawing; this term represents the
practice of drawing diagonal lines representing the interior
of an object, shown as a piece cut in half or
when a piece is broken away. This is done to make
more of the parts show, or to exhibit more clearly the
nature of the materials; hence section lining and cross-hatching
tell the same thing, i. e., the drawing of diagonal
lines, usually at an angle of 45°, to show that the
object is broken away and the interior designed to be
represented.
Cast iron.
Fig. 251.
Wrought iron.
Fig. 252.
Steel.
Fig. 253.
Composition.
Fig. 254.
Vulcanite.
Fig. 255.
Wood.
Fig. 256.
Leather.
Fig. 257.
Brick.
Fig. 258.
Fig. 259.
Figs. 251 to 258, inclusive, show the section lining
and cross-hatching by which it is customary to represent
the various materials entering into a construction.
In fig. 259 is outlined a
representation of a section of
a cog-wheel; section 1 being
the wood cogs; 2, the iron
wheel, and 3 the wedges at
the root of the gear. It would
be impossible to convey the
same ideas by ordinary plan
or elevation drawing; all the objects on the same page
are more clearly represented by the use of section
lines or cross-hatching.
Sectioning is executed by drawing a series of parallel
lines about 3⁄32 inches apart. Lay the 45° triangle
on the upper edge of the T-square and draw the top-most
line of the sectioning. Then slide the triangle
along the T-square for each successive line. The sectioning
should be inked in without previous penciling
and the lines should be finer than the lines of the general
drawing.
Various devices are in use for mechanically equalizing
the distances in section lining, but the trained
eye is the most practical method. When two abutting
pieces are sectioned, the section lining on one piece
slants in an opposite direction to that on the other.
To draw an object to be sectioned on both sides
of its center line, only one side is sectioned, while the
other side is drawn in full.
Sections are necessary in nearly all machine drawings;
they are usually taken horizontally or vertically,
but they may be taken in any direction; the position
of a section should be shown by a line upon the object;
this line is called the cutting plane.
In fig. 261 is shown the hub of a wheel, it is also a
sample of work for practice.
Fig. 260.
Fig. 261.
Fig. 260 shows the mode of representing two
different materials in one plane, or a section may be
represented by the darker portion, and the lighter
shaded portion being a surface resting on the section.
Fig. 261 shows the section of a shaft surrounded
by the surface of a wheel.
TINTS AND COLORS.
For special purposes of illustration drawings are
made which must be tinted. In such cases the paper
must be expanded and stretched evenly all over its
surface; otherwise when the moist tint is applied the
paper will wrinkle and get out of shape; to do this
cut the paper at least half an inch less in size than the
drawing board; lay the paper face down, turn up a
margin or edge of about three-fourths of an inch all
round, then dampen the paper with a sponge and clean
water; allow it to soak for a few minutes until it is
evenly dampened or moistened all over, turn the paper
upside down (face up).
Apply strong paste to the under side of the margin
all round; rub down, on the drawing-board, working
from the center of the board outwards so as to exclude
the air and prevent creases or furrows. The board is
then inclined and left to dry slowly; make sure that the
paper is all well pasted and every part of the edges
attached to the board.
If tracings are required to be tinted or shaded,
the color may be applied before the tracing is cut off,
or what is more usual, the color may be applied on the
back of the tracing; then there is no liability to wash
out the lines.
Mechanical drawings are seldom tinted, but are
mainly produced in India ink. Where, however, a fine
effect is desired, working drawings are colored, so as to
show at a glance the material of which the different
parts are to be made.
The colors required are few but should be of the
best quality. Besides India ink the following water-colors
are generally used:
1, Neutral-tint. 2, Prussian Blue. 3, Chrome
Yellow. 4, Gamboge. 5, Raw Sienna. 6, Carmine.
7, Vermillion. 8, Venetian Red. 9, Sepia. 10, Indigo.
These come in hard cakes.
Certain colors and tints represent different metals
and materials as follows:
Wrought Iron—Prussian Blue.
Steel—Carmine and Prussian Blue, mixed to give
a purple shade.
Steel Casting—Same as the above darkened by
Venetian Red.
Cast-Iron—Neutral Tint made of India Ink, indigo,
mixed with a little carmine.
Brass—Gamboge or Chrome Yellow.
Babbitt—Emerald Green; sometimes light mixture
of India Ink.
Copper—Purple Lake.
It is sometimes found necessary to prepare a highly
finished and shaded drawing of the work in hand.
Such elaborations, in fact, are much admired by the
uninitiated, although the complete shading of the
drawing is no criterion as to the scientific value of the
machine. An illustration of this is told in the note.
Note.—A consulting engineer had to lay before a board of
directors plans of horizontal engines for their consideration. One
of these drawings was of a very superior machine, but being only
depicted lineally was at once rejected by them, for a highly
finished representation of a very inferior apparatus. The engineer,
wishing to induce the board to decide for the best, suggested that
the matter should be postponed to a future day, and in the meantime
had the drawing of the superior machine highly colored and
finished. At the next meeting the directors unanimously decided
that this was the very one which they preferred and had chosen.
