An equipment for mechanical drawing, except the instruments, can be
easily made in the shop by any boy who has had some practice with tools.
The drawing board is the first thing needed, and several makes are in
use, the object of all of them being to insure a true flat surface by
overcoming the natural tendency of wood to warp.
Shrinkage will take place in spite of all precautions, but this is not
a serious matter, and does not affect the usefulness of the board.
All boards, it is conceded, should be "built up," rather than consist
of one piece. The idea is that the warping of one piece is somewhat
counteracted by that of the adjoining pieces in other directions.
Fig. 206 shows three forms in common use. At _a_ the ends are united to
wide cleats by a tongue and groove joint.
In shrinking and expanding with weather changes, the board is free to
slide along the joint, being glued only at the centre.
[Illustration: Fig. 206. The drawing board]
At _b_ two dovetail-shaped strips are inserted on the under side
across the grain. This is more difficult cult to make on account of
the shape of the groove, but it is otherwise satisfactory. At _c_ two
strong cleats are fastened across the under side by screws. This is the
easiest and least satisfactory method, as the cleats are often in the
way, making the board clumsy, and furthermore it does not allow for
shrinkage, unless the screws are secured in grooves instead of in plain
holes.
A good proportion for a small board is 24 × 18 inches. If the first
method of construction is decided on, glue up four or five strips of
well seasoned white pine, 7/8 inch thick, of the width desired, and
four inches shorter than the final length of board. Place in clamps
for twenty-four hours, and when dry dress down perfectly true to a
thickness of 3/4 inch. Test for warp and wind, and square the ends.
Square up two pieces of stock 2-1/2 inches wide, with a length equal to
width of board. For the tongue and groove joint, a set of tongue and
grooving planes will be necessary. Two cutters for this purpose come
with the modern universal plane, and if available this may be used. In
either case, set the depth gauge at half an inch, and plow a groove on
one edge of each strip 1/4 inch wide to the full depth, as shown at
_d_. On both ends of the board, plane the tongue same size as groove at
_e_. Coat the tongue at each end of board with glue for a distance of
six or eight inches at the centre, fit the end strips in position, and
place in clamps over night. When dry, give the surface a final truing
up, and also the ends, as the clamps may have made a slight change.
Go all over the surface with a sand-paper block, using 00 sand-paper,
and shellac the board all over. When dry rub flat with the sand-paper
block. Make a final test for any possible inaccuracy, and the board is
ready for use.
T square and triangles may be made, but as rubber or celluloid
triangles are better in some ways than wood, the former are recommended.
The T square is a very pretty little problem in woodwork, and may be
made as follows:
[Illustration: Fig. 207. T square and triangles]
The design for the head may be either _a_ or _b_ (Fig. 207), a being
simply a rectangular piece of hard wood, with two rounded corners; _b_
is laid out as shown, sawed near the line and curved side finished with
spokeshave. The straight side should be _perfectly_ straight, as any
variation will give horizontal lines out of parallel.
The blade may be of one piece, or built up. A very satisfactory
combination is to make the head of black walnut, and the blade of hard
maple, with black walnut edges. It will pay to make a special shooting
board for this work, and to make several T squares at the same time.
This shooting board should be slightly longer than the blade. (See Fig.
206.)
Gauge a line at a distance _x_ from the edge, equal to the width of 2
inches, and tack a straight strip of wood up to this line as a guide.
When the blade has been planed to its thickness of 1/8 inch, it is to
be placed in space _x_ and planed to width.
To plane a piece of hard wood down to an eighth of an inch, tack it to
a pine board with three 1-inch brads. The location of these brads can
be such that only one hole will be left in the blade to be filled up
afterward. One should be in the position of the central screw over the
head, the second at the point where hole _h_ is to be bored, the third
at about the centre of the blade. Set these brads slightly below the
surface, and dress down smooth.
When tested and found true, lift the blade by inserting a knife blade
under it, again fasten to the board with unfinished side up, and again
dress down. Before removing from the board, lay out the curved end to
correspond with the curve of the head, and cut to line with a chisel.
Remove from board, finish curved end with sand-paper block. Bore hole
_h_ for hanging up, locate holes for screws, and drill just large
enough to allow 1/2-inch round-head brass or blued screws to pass
through. In attaching the head, make sure that the two parts are at
right angles, and use thin copper burrs or washers under the screw
heads.
If the blade is to have edges of a different colour, joint the maple on
shooting board, and glue the strips to it, before planing to thickness.
This should be done on a flat board, with paper between it and the
blade. Glue the three pieces together, and drive 1-1/4-inch brads up
close to and touching the outside strips, at intervals of four inches.
By bending these slightly over the blade, considerable pressure will be
obtained, tending to keep the pieces together while glue is hardening.
Then proceed to dress down, and true up as before. When the process is
once learned, considerable pin money may be made by disposing of the
squares, and that will help to buy material for other things.
Triangles made from single pieces of wood are absolutely unreliable.
Referring to Fig. 207, the 45-degree triangle shows the grain running
up and down. As shrinkage takes place _m_ will not change, but _n_
will, and this will alter the angles; and besides a piece of thin
wood this size will warp and make the triangle useless for mechanical
drawing.
The 30-60 triangle illustrates the usual method of constructing a
wooden triangle.
Aside from bisecting the 90, 60, and 30 degree angles to get the
mitres, these joints, if simply glued, will be too weak for practical
use. The edge view and dotted lines indicate a thin feather of wood
glued into a saw cut made through the edge of each corner, the usual
method of strengthening. It is a delicate operation, and is only
recommended to boys who are fond of fine work.
A very serviceable section liner may be made from a wooden triangle by
carefully cutting out of one side a rectangular opening, as shown in
the detail. Make a piece of thin wood to fit this space, but 1/8-inch
shorter, and fitted so as to move freely. By moving this block and
the triangle, alternately, vertical or oblique lines can be drawn for
sectioning, and they will be equally spaced. Other blocks varying in
length will give a variety of spacings.
It is possibly one of the cheapest section liners, and the most
satisfactory within the means of any one. Irregular or French curves
may be made in thin wood. They should be drawn on the surface, sawed
out with the coping saw, and sand-papered smooth. As their thickness
should be but a trifle over 1/16 inch, they are very frail and easily
broken. These curves can be easily made in sheet aluminum, and they
will be much more satisfactory. This metal is handled similarly to thin
wood, except that the saw must be a metal cutting blade.
Triangles may be made of the same material. Lay out the form with a
sharp steel point or scriber, saw as close to lines as possible, and
with a fine file finish to line. Then smooth the curves with fine emery
paper wrapped around a lead pencil. To make straight edges, as on
triangles, lay a sheet of emery cloth on bench, and rub triangle back
and forth.