Squaring the corners of a mortise is a make or break moment.
If you don’t place the chisel just right — or put too much pressure the wrong way — it’s easy to bruise an edge or go past your layout line.
That’s why I always use the “swivel trick” when it comes to corners.
Here’s how it works:
- After you’ve cleared the bulk of the waste and are ready to pare down to your lines, make sure to use a chisel slightly NARROWER than your mortise. Stay away from the corners.
- Once the bulk of your edge is pared square, place one corner of the chisel in the mortise at an angle. Keep the flat back of the chisel flat against the inner wall.
- Keeping the chisel flat against the inside mortise wall, slowly swivel the chisel so the corner of the cutting edge comes down into the mortise corner and cuts off the last bit of material.
- Repeat this process to clean up the corner all the way to the bottom of the mortise.
The key here is control on the swivel.
Take only a little material at a time — and you’ll end up with clean, square corners.
February 16, 2023
Excellent technique, as always, sir. I basically do the same, but I often leave a tiny bit of waste at the top, perhaps a 16th or so in both directions, and clean up this last bit with a nice sharp-tipped marking knife. Keep up the good work!
Katz-Moses Disciple and Occasional Marking Knife Mis-User