A drawing-board should be made of well seasoned pine of a convenient
size, say 23 × 16, which will take half a sheet of imperial paper,
leaving ¹⁄₂-inch margin all around.
The working surface of the board--or its front side--should be perfectly
smooth, but instead of being flat it should have a very slight camber,
or rounding, breadthways, this latter feature in its construction being
to prevent the possibility of a sheet of paper when stretched on its
surface having any vacuity beneath it.
The _four edges_ of the board need not form an exact rectangle, as much
valuable time is often wasted in the attempts to produce such a board;
but it will answer every purpose of the draughtsman so long as the
adjacent edges at the lower left-hand corner of it are at right angles,
or square to each other.
An English authority recommends the use of two drawing-boards, 42 inches
long and 30 inches wide, made of plain stuff, without cleets, 1¹⁄₄
inches thick--seasoned--with edges perfectly straight and at right
angles to each other. _With two boards, one may be used for sketching
and drawing details and the other for the finished drawing._
The board should be ³⁄₄ inch in thickness, and fitted at the back, at
right angles to its longest side, with a couple of hardwood battens,
about 2 inches wide and ³⁄₄ inch thick; the use of these battens being
to keep the board from casting or winding and to allow of its expansion
or contraction through changes of temperature. This latter purpose,
however, is only effected by attaching the battens to the back of the
board in the following manner: ... At the middle of the length of each
batten--which should be one inch less than the width of the board--a
stout, well-fitted wood screw is firmly inserted into it, and made to
penetrate the board for about ¹⁄₂ inch, the head of the screw being made
flush with the surface of the batten; on either side of the central
screw, two others, about 3¹⁄₂ inches apart, are passed through oblong
holes in the battens, and screwed into the body of the board until their
heads are flush with the central one; fitted in this way the board
itself can expand or contract lengthwise or crosswise, while its surface
is prevented from warping or bending.
[Illustration: Fig. 141.]
A further improvement in such a drawing board as above shown is made by
cutting lengthwise along its ends a narrow groove and inserting an ebony
or hardwood strip; this is cut or sawn apart at about every inch to
admit of contraction; this strip serves as a guide to the stock of the
drawing square, allowing an easy sliding movement.
To produce really good work in the shape of a mechanical drawing, one
perfect straight edge only is required on a drawing board, and that the
left one, which is always known as the _working-edge_; but for the
convenience of being able to draw a long line across the board at right
angles to its lower edge, this edge is made truly square with that on
the left side of the board.
The details for building these drawing boards are given, because they
are easy to be made by one who understands the use of a few wood-working
tools; while the boards themselves are difficult of transportation--in
case of the change of residence of their owners--quite unlike the
instruments which are to accompany them.
Fig. 141 represents the board which has been described in the text, with
provisions for the contraction and expansion; the very dark lines are
intended to represent the ebony insertions--as described. Fig. 140
represents a plain pine board with dovetailed battens.
[Illustration: Fig. 142.]
Fig. 142 represents the common means used to attach or secure slightly
or temporarily the drawing paper to the drawing board; these are called
thumb-tacks, and are usually forced through the paper into the wood by
the hand, whence they are easily detached. These are made to have as
slight a projection as may be, so as not to interfere with the free
movement of the tee-square.
For mechanical drawing the invariable practice is to secure the paper on
which the drawing is to be made to the drawing board by pinning it; this
is effected by various kinds of _drawing pins_ or _thumb-tacks_.
The best kind for this purpose have a head as thin as possible without
cutting at its edges, slightly concave on the under side next the paper,
and only so much convex on its upper side as will give it sufficient
thickness to enable the pin to be secured to it; better use four or more
small pins along the edge of a sheet of paper, than use one clumsy,
badly made pin at each end.
[Illustration: Fig. 143.]
[Illustration: Fig. 144.]
Fig. 143 and fig. 144 represent a pair of plain trestles or horses in
common use for supporting large size drawing boards. This pattern is
found frequently in the laying-out shop. Fig. 145 and fig. 146 represent
_adjustable_ horses or trestles--these are designed, primarily, for
office use. As will be seen by viewing the illustration, the upper part
is supported by two hard-wood sliding pieces; these are provided with
strong pins and numerous holes, and pass through the frame of the
trestle, as shown, so that the upper portions can be arranged at any
angle convenient to the draughtsman, as he lies over his work or stands
by it.
[Illustration: Fig. 145.]
[Illustration: Fig. 146.]
Fig. 137 is introduced to exhibit the paper attached to the drawing
board with the thumb-tacks, and with the T-square and set-squares
arranged to commence work; the paper should not extend to the edges of
the board; three, four or more tacks may be used on each edge of the
sheet of paper, instead of two, as shown in illustration.
[Illustration: Fig. 147.]
A most convenient--and except for its extreme lightness, which is not
good in a drawing stand--a most admirable device is shown in fig. 138.
The drawing table is simply a drawing board with folding legs; these are
made from hard-wood, while the top is made of soft, seasoned pine, with
square corners; while the device is strong and well braced, it can be
folded and easily carried about--all as shown in the illustration.
[Illustration: Fig. 148.]