Making a wooden set-square

 A very basic tool for joinery work and easily made from a stable hardwood. I made mine from two pieces of kiln dried beech.  The stock or handle is 9 1/2 inches long by 2 1/8 inches wide and 1 inch thick. The blade or tongue is 14 inches long, 2 inches wide and 1/4 inch thick. Bob Rozaiski mentions that a good size ratio of handle to tongue is 2 : 3.

Beech set-square with a blade or tongue length of 14 inches.

The preparation of the handle and tongue took most of the time to ensure they were straight and square. The reference faces are chosen as the inside faces as they are more difficult to adjust after the square is glued. The handle was finished first including squaring and planing the end grain. The tongue was carefully planed down to 1/4 inch thickness. Next the mortice for the tongue was cut in the handle allowing the top of the tongue to rise about 1/4 inch above the blade and to protrude out of the blade for trimming later. The mortice wood was removed using a fret saw and the bottom of the mortice trimmed with a 6 mm chisel making sure that the outer edges of the bottom were above the centre, i.e the base of the mortice was concave. to make adjustment of the set-square easier. Once cut, the tongue was tried in the mortice and adjusted to get a close fit by either planing or filing the tongue. It was then firmly seated in the mortice and the 90 degree angle checked using another try-square. The adjustment was made by chiselling slithers of wood from the appropriate bottom of the mortice,

The tongue was then glued and clamped in place checking that the inside edges of the set-square were at 90 degrees. I used fast-setting polyurethane glue. The next step was to mark the position of three dowels to further attach the handle and tongue. I used 8 mm oak dowels and a 5/16 inch bit in the brace drilling from both sides. These were glued in place and then sawn and chiselled to get a smooth fit to the handle faces. The section of tongue protruding from the side was planed off and finished level to the handle.

The piece was finished by chamfering the top of the handle (1/4 x 1/8 inch) on both sides and making a curved portion at the end of the tongue. The angle on the outside of the square was checked and adjusted as necessary by plane or file. A hole was also drilled for storing the square. Finally, the wood was treated two times with boiled linseed oil.

I've made two other smaller set-squares, with about 8 inch tongues and 1 inch wide stocks and keeping the 2:3 ratio. These were made in the same way as the larger square taking care to get a tight fit of the tongue to handle.

Smaller set-square with 8 inch tongue.