Slide the stretcher bars together to assemble your frame. To make the process easier, look at each stretcher bar to determine how to slide them together. The printed side of the stretcher bars is the back, and the unprinted side is the front of the frame. Each long stretcher bar should be connected, top and bottom, to a shorter stretcher bar, and all of the printing should be on the same side of the frame.
Make sure the frame is square by measuring the frame diagonally, from corner to corner, on each diagonal. If the measurements match, then the frame is square. If they don't match, make sure that the stretcher bars are slid all the way together by tapping on the corners with a rubber mallet. Then measure again.
Lay the canvas, face up, on your work surface.
Put the frame on top of the canvas and center the frame.
Fold an edge of the canvas over one corner of the frame. Mark where the corner of the frame touches the canvas. Do this with all the corners of the frame.
Remove the frame and turn the canvas face down on your work surface.
Lay the frame on the canvas again, and line the edges up with the marks you just made. Make sure the printed side of your stretcher bars is facing upward.
Fold the canvas around the one of the longest stretcher bars and staple it in the middle.
Pull the canvas around the other long stretcher bar until there is a ridge in the center, and staple it in the center of the stretcher bar. Repeat this step with the short sides of the stretcher bar.
Staple the canvas on each stretcher bar two more times, placing one staple on each side of the staple you added in the previous step. Make sure you pull the canvas tight while you staple. Keep repeating this step until you get 1 inch away from each corner.
Fold in the point of the corner of the canvas, make a crease, then fold the edge of the excess canvas over the corner of the canvas and staple it down. This is a lot like making a hospital corner when making a bed. You want the folds to be tight and sharply creased so they look tidy. Do this to all four corners.