unattached compound mitre jig

When I designed the frame for my poster of the cover of The Great Gatsby, I wanted to use a compound miter joint on the corners in order to give more visual interest to an otherwise plain picture frame. I already had a nice hand miter saw, but it can only cut simple miter cuts. So, I designed a set of clamps that would attach to the frame of my saw and hold the wood at the proper angle.

a piece of wood being sawed using the clamps disassembled jig

The clamps can be set to five angles, 45, 36, 30, 22.5, and 15 degrees (corresponding to the angle presets on my miter saw). The angle of the clamp is set by the hole in the back of the clamp base: there is a screw in the back of the wood clamping mechanism that goes in to the holes in the base and can be removed and then replaced to make the adjustment. The machined parts are made of some waste Corian (solid-surface countertop material) we had at my work. I also designed a piece that can attach two of the clamps in order to make a simple corner clamp. To use the clamps with the saw, I attached two clamps on one side, placed as far apart as possible. I also put a piece of foam underneath the thumb screws to keep from denting the wood. Ideally, I'd use a long enough piece of wood that I could put at least one clamp on each side of the blade to make the cuts a little cleaner, but I didn't have enough wood for that on the frame project.

corner clamp assembly

I ended up breaking one of the clamp bases by dropping it, and also broke three of the tabs that help clamp the bases to the miter saw frame. So, I redesigned the bases to be a little thicker and changed the geometry of the clamping mechanism a bit. I think Corian is fine to use in the wood clamping mechanism because the parts are pretty thick and not subjected to very high stresses, but the bases should really be made of a less brittle material, like aluminum. I plan on making an aluminum version of the bases some time in the future, and also switching out the nylon thumb screws in the bases for steel ones so that they hold a little better on the saw frame. I might also get some all-thread to attach between the bases so I can make the clamps a little more stable when using two or more clamps at once.

jig attached to saw