Instructions for building your own canvas supports. This part shows how to build the support, part 2 shows how to stretch the canvas over it.
The advantages of building your own are: no size limit, any apsect ratio, choice of canvas and primer, cheaper than purchasing bespoke supports. The disadvantages are: cost of tools, time.
A claw hammer. Electric circular mitre saw. Quality mitre clamps. Tape measure. Jigsaw or handsaw (for cutting corner plates).
I recommend avoiding the cheap mitre clamps you'll see in hardware shops and market stalls. The M140 2" corner clamp from Record, are more expensive but are precise and sturdy (there's also a larger version).
For small to medium sized canvases I use wood with an 18mm depth and 40mm width. Try to avoid wood with knots and be sure it's fully dry - else it may warp later. Test the wood for straightness by placing one end on the ground and the other up to your eye and looking along its edges. Large supports need cross sections, take this into consideration when buying.
Quadrant is attached to the wood to keep the canvas free from the face of the support. Generally the flat side of the quadrant will be slightly less than the depth of the wood.
Plywood for corner plates to maintain corner strength. Plywood around 4mm thick is good. Don't use hardboard because it is too hard to hammer pins through.
Oval nails longer than depth of wood plus quadrant. Wood glue.
Step 1 - attach quadrant
Make a thin trail of wood glue along the wood as shown in fig.1.1. Then attach the quadrant as shown and hammer the oval nails in, roughly 6 - 7 inches apart along the length while maintaining alignment. Don't hammer the nails all the way as they need to be removed once the glue is dry. Wipe off excess glue.
Once fully dry you can remove the nails using the claw of the hammer (Fig.1.2). Be carefull not to damage the top edge of the quadrant with the hammer head.
Now is a good time to cut the right-angled trianglular back plates. The short edges can be around four inches. Use a jigsaw or handsaw for this.
Step 2 - cutting the mitres
Set the angle of the mitre saw to 45 degrees. Clamp the appropriate end of your wood (see fig.1.3) securely to the mitre saw, the quadrant should be against the clamping surface, and the bottom should be flat against the saw's table. Make the first cut.
Unclamp the wood and place the end of the tape measure at the quadrant side of the angled cut. Measure required length and mark with a pencil where it can be seen once clamped again. Change the saw to cut at the opposite 45 degree angle to the first. Line up the edge of the saw blade nearest to the first cut, with the mark, then clamp and cut. Repeat the entire process until you have four pieces, each with the longest edge being that of the quadrant.
Step 3 - clamping the sides together
Set your lengths of wood out so they form a frame. Next, clamp each corner, aligning each inside end with the inner corner of the clamp. Don't expect perfection. You can file the outside corners later if they don't entirely align.
Once the four corners are clamped satisfactorily, unclamp two of them to remove one side and apply wood glue to the face of the joins and reclamp securely. Do the same with the opposite side, wipe off excess glue and allow to dry.
Once dry and with the frame still clamped, hammer in a nail or two on each corner. Be careful where you place them or the wood will split. Unclamp the frame and glue plywood corner plates on each corner (away from outside edge) and using nails/pins, fix them in place.
Step 4 - cross sections
This step is required only for large canvases. I've not written it yet. You'll need a sharp chisel. In the mean time, fig.1.5 illustrates the basic idea.
Canvas + Support How To Part 2