How to mark out a mortise using a mortise gauge

Shop for Mortise Gauges

Step 1 – Prepare workpiece

If marking a mortise to be joined with a tenon, you will have already marked and cut out the tenon on another workpiece. Position your workpiece for the mortise on a flat surface.

Step 2 – Set fence

Decide where on the workpiece the mortise will be cut out. Turn the thumb screw on the fence anti-clockwise to release the fence and move it to the correct measurement then turn the thumb screw clockwise to secure it in place.

Step 3 – Set mortise gauge

Adjust the one marking pin by turning the pin adjusting screw anti-clockwise and pulling it to the required position. If you have your tenon you can use it as a guide for the pins. Turn the screw clockwise to secure it in place.

Step 4 – Mark workpiece

Tilt the gauge in the direction you wish to mark, and drag the tool across the workpiece, either applying pressure to both pins at once or to just one.

Marking both lines at once is more difficult and can lead to the lines being less accurate or one being less visible. It is easier to mark one line first, then go back and mark the other, tilting the gauge slightly to rest each pin separately on the wood.

Step 5 – Mark connecting lines

To mark a mortise you will need to mark the end lines as well. To do this, readjust the one marking pin so that the pins now line up with the tenon’s width. Then mark the wood, dragging the gauge so that the lines connect to the previous lines made. You should now have four lines marked out making a rectangle.

Step 6 – Cut out mortise

The mortise can now be removed, most commonly using a chisel.