[XXVI]
THE MITRE BOX AND PICTURE FRAMES
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.
Fig. 145. The 45° mitre box and test pieces