PREPARATION OF THE DESIGN AND SETTING OUT THE FULL-SIZED DRAUGHT.
In coach-building, as in building construction, the first thing to
be done is to prepare a design of the vehicle proposed to be built
according to the requirements of the customer. A scale of one inch to
a foot is a very good one for the purpose, though the scale drawings
are more often made to a scale of one and a half or two inches to a
foot. These drawings (or draughts as they are technically termed),
are prepared by specially trained draughtsmen, and it requires no
mean skill to produce, on a small scale, a pictorial representation
of the future vehicle, truly proportioned in all its parts, and a
delicacy of touch in order that the parts may not look coarse. These
drawings, if well made (and they generally are), give a very accurate
picture of the carriage, and a purchaser is generally able from this
to say what peculiar feature he requires, or where he thinks it
should be altered; if he can do this it saves a great deal of trouble
in the future, whilst the coach is being built.
For this work the draughtsman requires a drawing-board and T
square, and two set squares; as he never has to prepare very large
drawings, a board of imperial size will be amply sufficient, and
the T square to have a corresponding length of blade. T squares are
made of a variety of woods, but the most serviceable is one made
of mahogany, with an ebony edge; the most important consideration
being that the edge should be truly “shot” from end to end. The set
squares should either be vulcanite or skeleton mahogany with ebony
edges; the latter are preferable, as they work more cleanly than
the vulcanite, which, unless kept very clean, are apt to make black
smears across the drawing. In order to fasten the paper down to the
drawing board, drawing pins will be required; they are simple pins
of iron or steel, with a large flat brass head; four is the number
required for each sheet of paper, one at each corner. A very much
better way to fix the paper down is to “strain” it to the board. It
is done in the following way:—The sheet of paper to be fastened down
is thoroughly well wetted, by means of a sponge or large flat brush,
on one side (which, it does not matter, but see that your board is
perfectly clean before starting); it should then be left for five or
ten minutes for the water to well soak into the pores of the paper;
when this is done, the paper will be quite limp. Now take a perfectly
clean straight edge, or the back edge of the T square, and turn up
one of the edges of the paper ¼ or ½ an inch against it; along this
edge run a brush charged with glue from the glue pot, or a piece of
ordinary glue dipped into boiling water and rubbed along the edge
will do just as well, and when you think there is enough sticky
matter to promote adhesion between the paper and the board, turn the
edge of the paper back on the board (without removing the straight
edge or T square), and quickly rub it with the tips of the fingers
until it goes down flat all along without any air bubbles: do this to
all four edges of the paper, and place in a perfectly flat position
to dry; and if the operation has been carefully conducted the paper
will be beautifully flat to draw upon, and there can be no fear of
its shifting. When the drawing is finished, all that has to be done
is to cut round the edges of the paper just inside the glued edge,
and take it off. A little hot water will take off the glued strip,
and take care to wash all the glue off at the same time, otherwise
a smaller piece of paper might stick in some important part, and the
drawing spoilt in order to detach it.
The draughtsman will do well to have a few French curves, for drawing
the “sweeps” or curved lines of the carriage bodies, and scales of
various sizes, which are slips of boxwood or ivory, on which are
marked at the edges various scales, from ¹⁄₁₆th of an inch to a foot
up to 3 inches to a foot; and last, though not by any means least,
a good box of compasses or mathematical instruments. We shall not
discuss the merits of the various kinds of instruments here, but any
one wishing to go into the matter may do so by reading “Mathematical
Instruments” in Weale’s Series. But we should strongly advise the
draughtsman to go to some good maker, as bad drawing instruments only
lead to bad drawing.
The drawing paper used should be of a kind having a slight gloss
on the surface, like “hot-pressed” paper, but without its granular
texture. This kind of paper is usually called a “board,” as Bristol
board, and kept in various sizes, and sold by all colour dealers.
Various names are given to it, but it is all pretty nearly alike.
[Illustration: Fig. 7.—Coach.]
The paper being fastened, the drawing is commenced by drawing the
ground line A (Fig. 7); from that set off the height that the body
is to be from the ground, indicated by the dotted line B, and draw
the line C, which is the depth of the rocker. This latter is the real
bottom of the vehicle, and from it is measured the height of the
seat, about 12 inches, shown by the dotted lines on the body. Then
from the seat measure 42 inches, the length of the roof D. Lay off 23
inches for the width of the door, and draw E and F. From F measure
28 inches, the depth of the back quarter G, and from E measure 25
inches, which will give the front quarter H. Now the curves or
sweeps of the body can be put in by means of French curves. From the
hinge pillar measure 26 inches, shown by dotted line I, and this is
the centre of the hind wheel, which is 4 feet 3 inches high. The
spring is 1¼ inches thick, and consists of 5 plates 42 inches long.
The opening between the springs is 12½ inches, the lower one being
clipped beneath the axle. Measure 12½ inches from the underside of
the axle, which will give the underside of the top spring. 1¼ inches
must also be allowed for the back bar J, and the pump-handle K will
be ½ an inch thick. Then draw the boot L in such a position that
the front wheels will lock or turn under it freely. This may be
found by drawing a plan of the wheel as shown, and with the centre
of the lock bolt produced to N, strike the lines M, and it will be
seen that the wheels will just clear the body, which is all that is
necessary. From this it will be noticed that the centre on which
the fore carriage turns is not in the same plane as the axle. This
is more particularly discussed in the chapter on wheel-plates. The
front wheel is 42 inches high, the springs the same size as the back
springs. The draught may be now completed from Fig. 7, after having
settled on the various heights and sizes, and can be inked in with
Indian ink. The dotted lines, being merely constructional, are rubbed
out when the drawing is inked in. To complete the drawing, the spokes
of the wheels must be shown. These should be neither too many nor too
few, but there is no rule which regulates their number, except that
there should be two to each felloe. Having inked the parts in and
cleaned the pencil lines off, the drawing is ready to be coloured.
The colours applied to the drawing are the same as will be used for
painting the carriage, so we shall not detail them here.
From this drawing is constructed the full-size draught, which is
prepared before a tool is touched. On the walls of the body-making
shop are large black-boards, 10 or 12 feet square, and on these the
draughts are prepared just in the same way as described for the scale
drawing, except that all the heights are marked up a vertical line
which runs through the centre of the doorway, and from this the
various widths are also set off. This and the ground line are the
first two lines drawn, and it is imperative that they should make
a perfect right angle with each other, otherwise the draught will
not be true, and the material worked from it will be wasted. This
full-sized draught requires the greatest care in preparation, as all
the patterns to which the materials are cut or shaped are taken from
it, even to the smallest parts.
[Illustration: Fig. 8.—Brougham with Cant-Board. S, Standing pillar
(developed). B, Bottom bar. R, Rocker. L, Seat.]
The full-size draught also differs from the scale draught, inasmuch
as all the details of the construction of the vehicle are shown as
in the accompanying cut (Fig. 8), which shows the construction of a
small doctor’s brougham, and Fig. 9, which shows the construction
of a landau. This latter is a representation of the working draught
for the vehicle, and, in fact, is a reduced copy of what would be
drawn upon the black-board in the shop, except that some of the minor
details are omitted to avoid confusion.
[Illustration: Fig. 9.—Landau.]