Determine the height and width of your finished canvas piece. These are the measurements you will use to cut your stretcher bars. For example, if your finished canvas will be 8 inches by 10 inches, then you need to cut two stretcher bars to 8 inches and two stretcher bars to 10 inches.
Select wood for your stretcher bars. Look for wood that is 1/2-inch thick. Pine works well for this project because it is easy to cut, readily available in most areas and inexpensive. You can save money by finding one piece of pine that is long enough to use for all four stretcher bar. For example, if you are trying to cut stretcher bars for an 8-by-10 inch canvas, you would buy a piece of pine that is 36 inches long (8+8+10+10).
Measure and mark the cuts to be made on your pine. Use a T-share to draw perpendicular lines across the pine for a straight cut.
Cut your rough stretcher bar blanks using a handsaw or an electric saw. Then use a protractor or polysquare to draw 45-degree angles across the ends of both sides of your stretcher bar. The angles need to angle inward, so when you assemble the stretcher bars, you create a kind of picture frame.
Saw the angle cuts on your wood.
Assemble your four stretcher bars. Apply a bead of wood glue to each angle cut edge and press the pieces together to form a picture frame shape. To provide a little extra stability use a staple gun to add two or three staples along the joints, inserting the staples from the broad face of the frame rather than the narrow face.