This is probably a common technique, with a name, but it only occurred to me today. I gave it a shot, and it worked out really well. I’m going to use it from now on for non-through cuts, and by that, I mean rips and crosscuts that don’t go from one end to the other, but do cut through bottom and top of the ply.
Basically, once I set the blade height, and fence, I run the cut up to a 2” mark I make from the leading edge. Then I back it out, flip it over, and measure the distance to the end of the cut on the bottom. I make the target mark on the top side, minus that difference, then cut to that line, which isn’t all the way to where I need it. Now the bottom of the cut is to the mark, but the top is a little shy. Now I can carefully cut the rest with a very thin kerf, handheld flush-cut saw, using the pull strokes from each end to avoid any tearout, and inching up to the mark on each side. It only takes a minute to finish up the thin wedge left over.
I got cuts to my marks that are within a couple thousandths of exactly right, and by pressing the flush-cut against the edge of the cut that I care about with both hands, one on each side, keeping the blade flat, the cut is inline, and indistinguishable from the circular saw’s cut. I guess this is how the old-school dovetailers did, and do it. Of course, I’m not going from scratch, but following a straight edge the saw already created, but I can see now that I’m able to walk up by hand far closer than I can when trusting machinery. I’m always amazed by that. Machines are supposed to be perfect! :)
I need this as I’m doing some stair-shaped cuts in plywood right now, some nice 3/4” baltic birch I picked up this week from a plywood store that I’m liking more each time I go back (I think I’ll make a little post on that later today). I need sharp inside corners, and this is giving them to me.
The project this is for will be documented as I get farther along, and then in stages, and I’ve a Sketchup model I’ll eventually post as well, but I’d like to have more progress first before spilling the beans, even though it’s just a simple little thing.
-- Gary, Los Angeles, video game animator