Old circular-saw blades make excellent knives because they are abundant, and you can pick and choose the thickness and composition of the blade. Circular-saw blades that work best for making most knives are composed of plain carbon steel with 1/16-inch thickness. For larger knives, a circular-saw blade for cutting concrete can be found up to 2 feet in diameter and with 1/8-inch thickness.
Design the shape of the knife and cut it from cardboard to use as a template. Make sure the cardboard template fits within the space of the old saw blade. Your template should include the shape of the handle along with the blade. Lay the cardboard design on the saw blade and trace it with a felt-tip marker. Avoid laying the template over the saw blade teeth. Lay the template close to the inside of the saw blade to take advantage of its full diameter; use the area closer to the teeth for a shorter knife.
Clamp the saw blade in a vice. Cut the knife blade along the outline using a rotary cutting tool. Use the highest speed setting on the rotary cutter, and stop frequently to lubricate the rotary blade with paraffin wax to keep it cool. Wear safety glasses at all times while cutting the blade.
Smooth out the sharp edges along the blade and handle on a grinder. File the edges smooth starting with a medium file. Change over to a finer file as the edges become smoother, especially on the handle and the side opposite the cutting edge of the blade.
Clamp the knife in a vice so you can use both hands for filing the bevel on the knife blade. The bevel is the tapering of the blade down toward the cutting edge. Add the bevel, but do not sharpen the blade yet. Multiply the blade thickness by two, then measure that distance from the edge of the blade to determine where to start the bevel. In other words, for a 1/16-inch thick knife, the bevel will begin 1/8-inch from the edge on both sides of the knife. Use a medium file to begin with, and then use increasingly finer files as the proper shape takes form.
Drill the pinholes for attaching the handle in a drill press. If making the handle from wood, dry out the wood by baking it in an oven at 65.6 degrees Cor several hours. This will prevent the handle from shrinking once it's mounted to the blade. Mount the handle by inserting the Corby rivets through the pinholes and screwing them together with a screwdriver. A Corby rivet is like a countersunk screw made of brass; sand away the Corby rivet screw head in the sander for a smooth finish on the handle. Complete the knife by sharpening the blade.
Avoid using saw blades with carbide teeth; make sure the whole blade is made from 100 per cent steel for best results.
Don't use high-speed steel saw blades and alloys like tungsten, cobalt, titanium or other exotic metals for making knife blades. These blades are not optimum for keeping a razor-sharp cutting edge.