Circular Saw and Straightedge Crosscuts
module: square is everything
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ok. last time we talked about why square matters. this time we actually make a straight cut, because talking about it doesn't build a side table.
i said in the tools lesson that you don't need a table saw to build good furniture. a circular saw and a straightedge will do most of what you need, and this is the lesson where i prove that to you.
the setup
here's the problem with a circular saw straight out of the box. you're guessing. you draw a line, you line up the blade by eye, and you cut. and your hand drifts, just a little, the whole way down the board. an eighth of an inch here, a sixteenth there. by the end of the cut you're not on the line anymore.
a straightedge fixes that. it's just a straight board or a metal rail that you clamp down as a fence, and you run the saw's base plate against it instead of trying to follow a pencil line freehand. the saw can't wander because it's got a wall to run against.
you can buy a nice aluminum track for this. you can also use a straight piece of plywood or a factory-edge board you know is true. i started with the plywood version because that's what i had. works fine as long as the edge is actually straight, which you should check, not assume.
measuring twice, and why i mean it
before you cut anything, measure your workpiece. then measure it again. i know everybody's heard "measure twice, cut once" so many times it's basically wallpaper, but here's what actually happens if you skip it.
i was cutting legs for a side table a while back. needed four legs, all the same length. cut two of them at 17 inches. went to cut the other two and my tape had shifted, or I misread it, honestly I still don't know what happened, and I cut them at 17 and a quarter. quarter inch off.
instead of just recutting them, I decided I'd sand the extra off. you cannot sand out a quarter inch. I want to save you that hour, because that's about how long I spent trying before I gave up and recut the legs properly. would've taken ten minutes if I'd just done it right the first time. stubbornness cost me the hour, not bad math.
so measure the board. measure it again before the saw touches it. and after you make your first cut, measure that piece too, don't assume the saw did exactly what you told it to. the board doesn't care what you meant to cut.
the actual steps
here's how i do a crosscut with a straightedge, start to finish.
- mark your cut line on the board with a square, all the way across, not just a tick mark on the edge. you want to see the whole line when you're cutting.
- figure your offset. your saw blade doesn't cut exactly at the edge of the base plate, there's a gap between the blade and the edge you're going to ride against the fence. measure that distance on a scrap cut first. write it down if you need to, i still check mine every time i switch saws.
- clamp the straightedge down on the offset line, not the cut line. use two clamps minimum, one on each end. if the board's long, add a third in the middle. a straightedge that shifts mid-cut is worse than no straightedge at all.
- support the workpiece so the offcut isn't just hanging there. if it's not supported, the piece can pinch the blade as you finish the cut, or it can snap off and drop before you're done, which is not a clean cut and can also kick the saw back at you. use sawhorses, use scrap underneath, whatever it takes so both sides of the cut are held up.
- set your blade depth so it's only about a quarter inch deeper than the board thickness. deeper than that and you're just adding more spinning blade below the wood for no reason, which is more exposed blade near your hand and the surface underneath.
- make the cut in one steady pass. don't stop halfway and reposition your hands. keep the base plate flat against the straightedge the whole way through, and keep your body out of line with where the blade would go if it kicked back toward you. it doesn't happen often, but it happens fast when it does.
- check your work. square, measure the length, compare it to its pair if you're cutting matching pieces, like legs. this is where that quarter-inch story earns its keep. check before you move to the next piece, not after you've cut all four.
Pocket holes and dowels get their strength from square, true cuts feeding into them. a joint can only be as good as the two faces you're putting together, and this is where those faces get made.
before next time
grab a piece of scrap and practice this cut a few times before we touch the actual side table pieces. get your offset dialed in on your own saw and get comfortable with the clamping, because next lesson we're cutting real parts and I'd rather you waste scrap than a good board.