Refining The Mortise Hole

The inside of the mortise hole does not have to be perfectly smooth; rather, just clean enough for the tenon to make decent contact when fully seated. Also, some ‘tooth’ (unevenness) inside the hole helps the glue to form a stronger bond.

To clean up the mortise hole, grip the chisel handle firmly with both hands and drag the chisel back and forth along the length of the mortise, making sure not to twist the chisel as it would bind and enlarge the hole. The sides of the chisel will trim any protruding fibres and make the walls somewhat more regular. If the chisel can move freely (with a bit of work) from one end to the other, you can be sure that the tenon will also fit snugly.