How to Mortise a Door Latch

If the door hardware to be installed includes a standard knob and latch system, it is better to cut them before the mortise. This can be done freehand but a jig makes this job easy. Instructions will come with the kit but here are general guidelines.

• Measure the height of the lockset from the floor and make an appropriate mark on the door.
• Select the setback on the jig to match your hardware.
• Clamp the jig onto the door.
• Chuck the large hole saw into the drill and cut the hole for the knob.
• Chuck the small hole saw into the drill and cut the hole for the latch.

• Chose the square or round cornered scoring tool and place it in the tool holder.
• Align the cutter with the hole for the latch barrel and strike the tool with a hammer.
• Hold the latch plate chisel in the hole for the latch barrel and tap it with the hammer, removing half the wood from the mortise.
• Reverse the tool, placing the chisel in the hole again and tap it to remove the other half of the wood from the mortise.
• Work until all chips are removed and the mortise is a uniform depth.
• If the mortise isn’t deep enough, repeat the process.

In some cases, it may be preferable to make the mortise before cutting holes for a standard knob and latch.

• If the face plate of the latch is removable, remove it, put it in place and trace around it.
• If the face plate isn’t removable, invert the latch and press the plunger against the door. Hold it in place and trace around it.
• If neither of these work, cut out a cardboard template for tracing, or measure and transfer lines to the door edge.

This job is best suited to a 1” wide chisel but any smaller size will work. Our example was made with 3/4” and 1/4” chisels.

Note: A chisel should never be driven or pushed toward any part of your body, including the support hand.

• Mark the location of the mortise on all sides.
• Begin by placing the flat side of the chisel facing outward, with the sharp edge on the line. Tap the chisel with a mallet or hammer, then move around the line to make the preliminary cut.
• If the corners are round, a curved chisel will help or you can work around the corner with a narrow chisel.
• Within the outline you just finished, make relief cuts across the area to be cut out. These cuts should be the same depth as the outline.
• Turn the bevel of the chisel down, or toward the door, and place the sharp edge at the start of the outline.
• Tap the chisel to begin cutting out the small pieces of wood.
• Work slowly and carefully so that you don’t lose control of the chisel and damage the door or cut yourself.
• Work until all chips are removed and the mortise is a uniform depth.
• If the mortise isn’t deep enough, repeat the process.

Put the latch into the mortise and hole.

• Be sure the beveled face of the plunger is facing the correct direction.
• Use a self-centering drill bit to drill pilot holes for the screws.
• Being careful not to over-tighten, drive the screws.
• If you accidentally over-tighten and strip the wood in the door, here's an easy fix. Apply wood glue to a golf tee or several toothpicks and drive them into the hole. Allow the glue to dry, then cut flush and drill the pilot hole again.