Near one end—about two inches in—lay out across the top with try square a line 90 degrees with the sides. Carry the line down each side, square with the top edges. For 45-degree angles, lay out a square by drawing two pencil lines across the top, as far apart as the finished mitre box is wide. Draw the two diagonals and square lines from their ends down both sides, taking care that their position is not over the screw in the bottom; because as the saw cuts deeper it may reach this screw and ruin its teeth.
Make the three saw cuts directly on the lines laid out with a cross cut or back saw, with the utmost care. If this is not done accurately, all the labour of preparation is wasted. The blank end of the mitre box may have an additional 90-degree cut, or be left for new cuts in the future, as a mitre box of this description wears out and becomes inaccurate.
Other angles may be used, as 60 degrees or 30 degrees, but it is better to have these on another box as they are used less, and for special purposes. ([Fig. 146].)
The mitre box is not ready to use until it has been thoroughly tested. Prepare a strip of soft wood—pine or white wood—11⁄2 inches wide and 1⁄2 inch thick. Cut four pieces from it on the mitre box, using the back saw as shown at a, with only one of the slits. Place these four triangular pieces together to form a square. All the four mitre joints of this square must fit perfectly. If they do not, mark the slit "N. G.," and test the other slit in the same way. If all right, mark "O. K." It often happens that one may be perfect and the other inaccurate. If they are both O. K., the box is ready for use. If one slit is useless, lay out and cut another on the blank end of the mitre box in the same direction, and test again.
Fig. 146. 30-60-90 mitre box
In testing a 30-degree cut three pieces of the strip should be sawed out, and when placed together they should form a perfect equilateral triangle, while from a 60-degree cut, six pieces are needed to form a hexagon.
These angles are valuable in inlaid work, and for getting out geometrical designs.
The 45-degree cut is indispensable in making the mitred corners of picture frames and in cabinet work.