It seemed to Harry that the shop was fairly well equipped, but Ralph insisted that they must have a mitre box before making anything else for the house.

The mitre box is, or should be, an instrument of precision, and although simple in construction, must be perfectly accurate, or it is useless. (Fig. 145.)

The illustration shows the common form, but elaborate affairs of iron and wood can be bought ready made. Every boy should make his own, for the practice, if for nothing else. The sides should be made of oak ⁷/₈ inch thick, 18 inches long, and 3¹/₂ inches high, the bottom of ⁷/₈-inch pine or other soft wood, the same size.

When squared up, the two sides must be tested by standing them side by side; then reverse one end for end, to see if they are alike. If not, find where the trouble is, and correct it.

It is especially important that the edges of the bottom piece be square and the sides perfectly parallel. This test can be made with the marking gauge. Sides are fastened on by boring and countersinking for three screws on each. After assembling, the whole thing must be tested as if it were a solid block. Top edges must be true and parallel.

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.

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.In making picture frames of simple cross section, it is first necessary to cut the rabbet (Fig. 147) with a rabbet plane. If this moulding is made by hand, the size of the picture should be measured, the length of all four sides added, and a liberal allowance made for waste.

In the figure, the triangles a a are waste, the rabbet being indicated by the dotted line. After the four pieces have been sawed out on the mitre box, they should be placed together on a flat surface, such as the bench top or floor, to see if the mitres fit perfectly. If they do not, one of them can be block planed to make a perfect fit, and the other three laid close together, as shown in the illustration.

The assembling is the hardest part of the operation, and many devices have been tried and some patented to hold the parts together while the glue is drying.Perhaps the surest way is to drill a hole in one piece of each joint large enough for the passage of a wire bung-head nail.

The undrilled piece is placed vertically in the vise. The drilled piece, after receiving a thin coat of glue, is brought into position horizontally, and the nail driven home.

Theoretically, the nail should catch at the first blow, but the horizontal piece will sometimes slip, even with the best of care. It is wiser to place this piece about ¹/₁₆ inch above its final position, to allow for this slip.

A method sometimes used is to glue near the ends of each piece a triangular block of wood, as shown at d. These must be left over night to harden.

The next day the whole four pieces can be glued and held together by four hand screws, as shown, until the glue is thoroughly hard. This method, of course, can only be used with plain moulding or that which is square on the outside.

Our boys tried another way that is commonly practised. They nailed oblong blocks to an old drawing board, as shown at e e, and then placed the picture frame in the centre, after gluing the joints, and driving wedges in between the blocks and the frame. Paper placed under each joint prevented the frame from being stuck to the drawing board by the glue forced out by the pressure.

This paper plan was learned by experience, as the first frame the boys tried had to be pried up from the board, and in so doing they broke it at two of the joints, so that it had to be made again.

It is well to remember in gluing mitre joints that end grain absorbs more glue than a flat surface. A priming coat should be applied first, and allowed to remain a few moments to fill up the pores. The second coat should hold fast and make a strong joint, but an excess of glue should always be avoided, as it must be removed after hardening, and glue soon takes the edge from the best of tools.

Very fancy frames should be avoided. A bevel on the outside or inside, or both, is about all the young woodworker should attempt in the way of ornamentation. Depend on the natural beauty of the wood, as a fancy frame draws the attention from the picture, which after all is the main thing. We should admire the man, not his clothes, the picture not its frame, although the latter should be neat and well made.

The finishing and polishing of frames is taken up in Chapter XLIX.