These tips will increase accuracy and decrease working time
Mortise jig with cob background

If you plan to do a lot of mortising, a benchtop mortiser saves time by boring square holes. But they're not always the easiest machines to operate—especially for first-time users—so apply these helpful hints for best results.

Bit and chisel offset

The mortiser's square hollow chisel and the drill bit inside it work in tandem: The bit removes most of the waste while the chisel pares away the edges and corners. Proper spacing between the chisel tips and bit ensures the bit clears a path for the chisel. Here's how to install them: Slide the chisel (with the bit inside) into the mortiser collar, inserting a dime as shown below to keep it from fully seating, and snug the setscrew. Next, raise the drill bit into the chuck until it seats against the chisel, and tighten the chuck.

Square bit with callouts

Finally, loosen the setscrew, remove the dime, and seat the chisel tightly against the collar while simultaneously squaring it to the mortiser fence, as shown below. Tighten the setscrew, and you're ready to cut.

Square bit with ruler

Add a quick hold-in

High-end mortisers use built-in rollers to hold a workpiece tight against the fence. You can add that workholding ability using a couple of Magswitch MagJigs. Simply secure two MagJigs on the cast-iron base as shown below. The magnets' rounded ends hold the workpiece against the fence without marring.

Mortise jig with holes in board

Lubricate the column

Most benchtop mortiser heads slide up and down on a dovetailed column. To minimize metal-on-metal friction, apply a lubricant that dries without leaving a residue, such as Bostik GlideCote. A lubricant that leaves a greasy or oily residue will attract dust, requiring more frequent cleaning and relubricating.

Spraying motise jige

Cut mortises deeper than needed

Because of the cutting geometry of the drill bit and chisel, they won't leave a perfectly flat-bottomed mortise (below). To avoid time-consuming clean-up of the bottom with a chisel, set the depth stop to bore 18 " deeper than the length of the tenon. This way, the extra wood will not interfere with full insertion of the tenon.

Board with slots cut, round at bottom