Measure the width of the 2-by-4-inch wood you'll use. It should be 2 inches wide, but a 2-by-4 is usually a few millimeters wider or shorter. Center the middle of the wood's width on a table saw's blade so that the saw is able to cut the wood in half lengthwise; take into account the width of the blade because the blade will take away a small amount of wood when it cuts.
Set the lock on the table saw so the 2-by-4 won't move and change the blade's angle to 45 degrees. Turn on ventilators if they are available, and put on safety goggles and a dust mask.
Double-check the table saw's settings, and revise them if necessary. When the settings are correct, turn on the table saw, and split the wood in half lengthwise. Turn off the saw immediately when you finish cutting.
Mark the wood at the point you need to cut to create each side of the canvas frame, starting at one end of one board and measuring inward. Make the marks on all the pieces of wood with a wood pencil. Use as much of one wood board at a time as you can.
Place the flat sides of the first board to be cut against the right side of the table saw. The diagonal cut should be closest to you and facing up. Move the saw blade to a 90-degree angle.
Align the table saw's blade with the first mark made on the wood. Put on the safety goggles and dust mask if you took them off, and turn on the table saw. Cut the wood along the first mark, and turn off the saw. Line up each next mark, and cut the wood until you make all of the pieces of the interior frame.
Move the angle of a hand saw to 45 degrees to the right side. Line up the first piece of wood you cut in Step 6 with the blade, and cut off the right corner. Cut off the right corner of each other piece of wood.
Adjust the hand saw to a 45-degree angle to the left side. Move the pieces of wood to the left of the saw, and line up the first piece of wood with the saw blade. Remove the remaining corners on the wood just as you did with the right side.
Check the fit of each stretcher bar by laying all of them on a flat surface in a rectangle. All of the corners should fit together to make a complete frame.