Two Techniques for Cutting a Mortise
There are two common techniques for mortising; one uses a succession of chisel cuts to remove wood in layers, and the other, known as the “Maynard” technique, starts by drilling a hole the same width as the mortise. Try them both and see which works best for you.
Begin by laying out the mortise. Stand behind or to one side of the workpiece, and start each cut about 1/8" from the end or from the previous cut; each cut is about 1/4" deep in hardwoods, 3/8" deep in softwoods.
Hold the chisel vertically with a relaxed grip on the handle. Ensure that its back is parallel with the end of the mortise.
Move the chisel 1/8" from the last cut, incline the handle slightly to chop about 1/4" deep, and use the chisel as a lever to remove the waste.
When you get close to the other end, turn the chisel around and chop vertically 1/8" from the end line to leave a small amount of waste for final cleaning up.
Repeat the previous steps until the desired depth is reached.
Last, drive the chisel straight down on the end lines to cut to final dimension and remove any bruising created when levering out the waste.
The Maynard technique employs the use of a drill to ease the start before chiselling. Start by marking out the mortise, and then follow these steps.
Drill a hole that is as wide and deep as the mortise and about 1/4" from the end of the mortise.
With the chisel bevel placed about 1/4" from the starter hole, tilt and drive the chisel in at an angle until it hits the bottom of the hole. Then lever the handle backward to remove the waste.
Move the chisel back towards you about 1/4" from the mortise hole, and chop in at an angle as before until it stops at the bottom.
Lever the waste out, and repeat the chopping and levering until you reach the end of the mortise.
At the end, chop the last waste with the chisel held upright, and lever the waste away.
To finish, make another upright chop at the other end where the boring started.