Building a Setsquare

This is a useful little tool which should always be made at home; it is simply a flat piece of board usually about inch thick, of which one a corner is a right angle. The grain of the wood runs in the direction, and ac is cut across the grain; the angle is a true right angle, and the other angles, as also the back, are rounded. There is a reason for this, namely, that wood shrinks in breadth across the grain, but it does not shrink in length to any perceptible extent. If the setsquare were cut from the board in such a way that the grain of the wood were in the direction, and were across the grain, and the angle at c were made a true right angle, at first the setsquare would be true; but in a short time the wood would shrink in the direction d, and the angle at c would be greater than a right angle; or, if this setsquare had been made from a piece of perfectly dry and seasoned wood, which had shrunk to its utmost extent, it would expand in the direction if the weather turned damp and the wood absorbed moisture, and the angle at c would be less than a right angle, thus the setsquare would never be reliable.

On the other hand, if the grain of the wood run in the direction &, the setsquare may expand or contract whenever it likes in the direction ac, without affecting the angle at c, which will continue to be true. When making the set- square, there will be some temptation to plane the side th straight, making the angles at a and b each 45 degrees, because it looks as if some day these angles may be useful. But let it be remembered that on account of the shrinkage of the wood these angles can never be reliable, and that therefore it is better to finish the set- square in the usual way, viz., the angle at a is rounded, as in the sketch, to strengthen that corncr, which would otherwise easily break off if the setsquare should accidentally drop off the bench. The corner at b is rounded to match the corner at a for the sake of appearance, and for the same reason the side at d is hollowed out.

Setsquares are also used for mechanical drawing. These are usually about inch thick, and are made with the angle at a to be 30 degrees, that at b 6o degrees, and the side ab double the length of the base 6c, the grain of the wood running in the direction a to c; of course the two smaller angles are unreliable, but they answer the purpose for drawing nuts for bolts, etc.; these setsquares arc usually made of what is called pearwood, and are the best. These squares are also made of vulcanite (prepared indiarubber), which does not shrink, and therefore the angles continue true; but they rub the pencil lines and dirty the drawing paper, and are therefore objectionable.

There is yet another variety of setsquare, which both retains its angles true, and also not dirty the paper; it is built up of three pieces of wood about 1 inch wide and j inch thick, which are jointed together at the angles; this variety is very pleasant to work with until it accidentally drops off the drawing board and is broken. The amateur would find the making of one of these built squares a nice piece of work. The ends of each piece of wood are cut to the half of the angle of that of the finished setsquare, as in the sketch; they are then clamped upon a piece of board, b and a saw-cut made down the angle. The angles setsquare at b and c are similarly cut, and thin pieces of wood or veneer are glued into the saw-cuts. The amateur, having now made all the squares he can want for marking out and finishing his box, he will have to cut up his board with his saw.