This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
A picture frame or triangle is quite difficult to hold together when fitting the corners. It is still more difficult to hold them together while the glue dries. The clamp illustrated will be found quite satisfactory in solving this problem, and at the same time is very-simple to construct and easy to manipulate. The material list for making the clamps and corner blocks is as follows:
Picture frame clamp:
4 pieces. 1 1/4 by 154 by 15 in.
2 pieces, 1 1/4 by 1 1/4 by 5 in. Triangle clamp;
3 pieces. 1 1/4 by 1 1/4by 10 in. 1 piece, l 1/4 by 1 1/4by 4 in.
4 pieces. 7/8by 3 1/2by 3 1/2 in. 8 pieces. 7/8 by 1 by 2 in.
The pieces mentioned are of oak. S-4-S.
1 piece 3/8-in. maple for dowels Hardware:
10 bolts. 1/4 by 2 in. 4 bolts. 1/4 by 3 in. 2 bolts. 3/8by 6 in.
The picture-frame clamp consists of the four arms A, B, C and D, Fig. 1. A 1/4-in. hole is bored in one end of each piece, 1/2 in. from the end. A series of 3/8-in. holes, 1 in. apart, are bored along the center in each piece. The two short pieces, E and F, have two 1/4-in. holes bored in their centers, 1/2 in. from each end. These pieces are bolted to the four arms with %-in. bolts as shown in the sketch. A %-in. hole is bored in the middle of each piece E and F for one of the 6-in. bolts K.
Ill: The Corner Blocks on Both Picture Frame and Triangle Clamps are so Constructed That They Hold the Molding together While Fitting the Corners and also Hold Them Securely While the Glue is Hardening
The four corner blocks G, H, I and J, Fig. 1, have a %-in. hole bored in the center of each and a dowel glued into it with the end projecting 1% in. on the under side and level with the surface on the upper side. Each of the corner blocks is fitted with two pieces like X, Fig. 2. Each of these pieces has one end round or a semicircle, and in its center a %-in. hole is bored. The other end has a %-in. hole bored 1/2in. from the end.
After making the small pieces, take the four corner blocks G, H, I and J and draw a line on the upper side in the center, with the grain of the wood, and mark the angles as follows, so that one-half the angle will be on each side of the centerline: On one end of the pieces G and H mark a 90-deg. angle, on the other end a 45-deg. angle, on the piece I mark a 90-deg. and 30-deg. angle and on J mark a 90-deg. and 60-deg. angle. Mark the number of degrees of each between the sides of the angle. Place two of the pieces marked X, Fig. 2, on each of the corner blocks, one piece on each side between the different angle lines, so their round ends will be toward the center and toward each other with a space of % in. between them. Clamp the pieces to the corner blocks and bore the 1/4-in. holes through them to secure perfect alinement. Put the bolts in and turn the pieces first to one angle and then the other, and while in the respective positions, bore the %-in. holes % in. deep in the corner blocks. Glue a dowel in each %-in. hole of the small pieces, allowing it to project 1/4in. on the under side so it will fit in the 3/8-in. hole in the corner block. Be sure to countersink the holes for the heads of the bolts. All bolts should be fitted with wing nuts. All that is necessary to change from one angle to another is to loosen the nuts and swing the small pieces around so the dowel pins will drop into the other holes, then tighten the nuts.
The triangle clamp is made in the same manner as the picture-frame clamp, except that the arms L and M, Figs. 2 and 3, are half-lapped into the crosspiece P. The bolt O is % in. and the head is cut off. Drill a %-in. hole in the bolt, 1/4 in. from the end, and bore a %-in. hole in the end of the arm N. Insert the headless bolt O in this hole and drive a nail through the side of the arm N, so it will pass through the hole drilled in the bolt. This keys the bolt in the end of the arm N.
To clamp a picture frame, set the corner blocks G, H, I and J to the 90-deg. angles and adjust them on the arms A, B, C and D to accommodate the size frame to be made, as shown in Fig. 1. Tighten the thumbnut on the bolt K, and this will draw all four corners together with the same pressure. The corners can then be examined to see if they fit properly. If they do not, saw in the joints with a backsaw until they do fit.
The triangles are clamped in the same way. The corner blocks are set to take the proper angles. The ends of the bolts should be slightly burred over so that the thumbnuts cannot be turned off. - Contributed by Chas. A. Pettit, Baltimore, Md.