Quite a few people have asked me if I build stretchers for other artists, and I have to say no. Then they sometimes ask how I do it, and I'm happy to explain. Now here is the illustrated version!
Today I began to build what I call "strong-back" stretchers. You can see one on the wall behind my work table in the photo above. They are mostly used for larger canvases, to avoid excessive cross-bracing.
Building strong-backs is a 2-part process. First the lengths of wood are prepared, then they are cut to the desired size and assembled into stretchers.
I like to use plywood because I ship my work to places where the humidity is very different from here. Because plywood is made with thin layers of crossed wood grain, it is less likely to warp and twist than a solid piece of wood.
Ordinary construction-grade spruce plywood is fine. It should have 6 or 7 layers of ply, and should not be terribly expensive.
To begin, I buy 2 sheets of 3/4" plywood at the lumber store. I have them rip one sheet into 2" strips, with a slight bevel (10-15 degrees) on one edge. The other sheet is ripped into 1 3/4" strips with no bevel. I take away one little pile of straight-edge strips, one little pile of bevelled strips. That's the easy part.
Now the idea is to glue one of each piece together.
Put some glue on the edge of a non-bevelled (1 3/4") piece. Make sure you use enough glue to get a good join.
Then lay a bevelled (2") piece on top and nail the two together. A nail every 12" or so should do it.
This is the profile you're aiming for. Ok, it's flipped upside down from how I nailed it, but you get the idea, right?
This is not a great glue join.
This one is better. A good glue join here is important - it will not separate when you begin cross-cutting.
Wipe off any excess glue, put it on the "finished" pile and continue along until all the strips are assembled. I let them sit overnight (sometimes longer) to make sure the glue is set before I begin the cross-cuts.
That's all for now. In a day or two I will cut and assemble the stretchers - stay tuned!