When stretching a piece of canvas onto a frame, you first have to position the canvas SQUARELY on the frame.
Then, pin the corners, around the back, in an area that will not show in the finished frame. This is to ensure that the final product will stretch SQUARE, and not twist the frame, as you stretch and staple. Very important that the frame does not end up twisting, or the corners being off-square.
Then, you make sure again that it is square with the frame, and then pin the canvas right in the middle of the frame stetcher bars on each side, so the tension that you feel is right (in the screen tightness) is evident.. in the middle of the screen. basically, it is stapled, once on each side, exactly in the middle of each rail, or stretcher bar.
then, you put one staple, on each side of that first staple, stretching the canvas over the bar(for a total of three staples, on that side!, at this point!), and towards the corner.. You are moving out from the center of the bar, towars the corners.
One staple, on each side of the area you are working on. Then, you move to the opposite side. Then across from one another.
To rei-terate... one side, the opposite, then the side not yet worked on (which is 90 degrees fom the sides you just did), then the last side. One staple, on each side of that fist center one. Repeat until done out to the corners.
Fold over the corners of the canvas, and then staple down that last bit (the coner bit will 'fold over' as there is excess canvas in the finished corner).
If you fail to do it this way, your frame will twist, and/or you will have consistency problems in your stretching or surface.
This from a friend who owned a artist's shop, who did all his own frames for re-sale. Huge ones as well. He lent me his air powered staple gun. I have my own compressor.
The amount of tension is up to you. Be realistic. remember, it will add up, so, some is DEFINITELY desired, just.. this is not a bicycle.. don't hammer the tightness until things break. Lotsa tension is not good. That will virtually guarantee twisting over time, as the thing settles. Besides, the paint drying (if you use any), will tighten the frame even more.
Not quite floppy canvas (not loose by any means, but a little more tightness desired) can be easily tightened to the exact right amount, when paint is applied to a canvas.
[This message has been edited by KBK (edited 08-11-2001).]