Think of it almost like a DIY track saw.
Crosscutting a full sheet of plywood on a tablesaw is pretty difficult, particularly when you don’t have any help. I use a circular saw and this shop-made edge guide, instead. The cuts aren’t finish quality, of course, but at least I end up with smaller pieces that I can more easily cut to final size on the tablesaw.
My guide is easy to use, and there are no loose parts. You just line up either end of its arms with a pencil line on the wood and you’re ready to go. One turn of a knob locks it in place.
I often cut a sheet on edge, still sitting in its storage rack, so I don’t have to lift it. When the offcut is quite large, I pull out the sheet and lay it flat on a 4×8 piece of 2″ foam insulation. The foam supports the whole sheet and can be re-used many times—mine has dozens of saw kerfs running across it.
The guide’s locking mechanism is composed of two pieces with opposing, beveled sides. The outer piece is fixed to the guide’s arm; the inner piece is loose, but attached to a knob. Tightening the knob draws the two pieces together, and because they’re beveled, forces the inner block to wedge against the plywood, holding the guide in place.
I determined the lengths of these pieces by measuring my circular saw. The long side of each one corresponds to the large offset to the left of the blade; the short sides correspond to the small offset to the right of the blade. The precise lengths of the offsets are important, since the ends of these pieces show you exactly where the saw will cut. This way, depending on the situation, you can cut on either side of the guide. There’s a fixed block at the lower end of the guide with the same offsets.
The guide is made from four pieces of hardwood; the fixed block and wedge parts are all 3/4″ x 3″ x 7″ (the length of these pieces may have to be adjusted for your saw). The straightedge is 3/4″ x 3″ x 56″. -Mark Thiel