Why is my circular saw cutting at a slight angle instead of square?

An edge that is out of square by a degree looks fine on its own and shows immediately in a joint, a mitre or a run of shelves. The cause is nearly always one of two things: the saw is not set up square, or it is not being held flat. Both are easy to check and neither is expensive to fix.

What you'll need

• Engineer's square or combination square
• Spanner or hex key for the bevel lock
• Scrap timber for test cuts

Step by step

1. Isolate the saw before you touch the blade.Unplug it, or remove the battery. Every check below involves putting hands and steel near the teeth.
2. Set the blade to maximum depth and the bevel to zero.Full depth gives the longest reference surface to check against and makes an error obvious.
3. Square the blade to the shoe against the plate.Stand the square on the shoe with its blade against the flat of the saw blade, between the teeth. Measuring against a tooth measures the set, not the plate, and will read out of square on a perfectly good saw. Look for light under the square.
4. Adjust the bevel and reset the stop.Slacken the bevel lock, bring the blade square against the square, and lock it. Then check the bevel scale: if it does not read zero, adjust the stop screw or the pointer so it does. A detent that lies is worse than no detent.
5. Check the shoe itself is flat.Lay a straightedge across the underside of the shoe in both directions. Pressed steel shoes distort if a saw has been dropped, and a twisted shoe cannot cut square however the blade is set.
6. Check for blade wobble.Spin the blade by hand and sight along it. Run-out from a bent plate, a chip trapped behind a flange or a bent arbor widens the kerf on one side and produces a cut that is not square through the thickness.
7. Make a test cut in thick scrap and check it.Cut a piece at least as thick as your usual work and check the cut face with the square. Test on the real thickness — an error of a degree is invisible in 12mm ply and obvious in 50mm timber.
8. If the saw is square but cuts are not, change how you hold it.Keep the whole shoe flat on the work throughout. Cuts go out of square when the saw is tipped at the start, when it rides up over a knot, or when one hand pushes down harder than the other at the end of a cut as the offcut drops away.
9. Support the work so nothing moves under the shoe.A workpiece that flexes downwards under the saw's weight tips the shoe. Foam beneath sheet material, or bearers either side of the line, removes the problem.

Tips

• Check the 45 degree stop separately. Squaring the zero stop tells you nothing about the bevel stop at the other end, and a mitre cut relies on it.
• If a cut is out of square along its length as well, that is a guiding problem, not a bevel problem — see the guides on cutting straight.
• A saw that has been dropped is worth checking end to end: shoe flatness, bevel, depth lock and blade run-out.

If it doesn't work