How to Cut a Mortise and Tenon by Hand

A mortise gauge and mortise chisel are keys to helping make this time-tested joint.

By Chris Gochnour #266-Jan/Feb 2018 Issue

Synopsis: To become proficient in cutting a through-mortise and tenon by hand, you need to use a mortise gauge and a mortise chisel. The mortise gauge is similar to a marking gauge but has two pins—one fixed and one adjustable—and a movable fence that can be locked in place to retain a setting. Mortise chisels are sturdy and can withstand the heavy mallet blows and levering required to remove waste. Chris Gochnour demonstrates how to lay out and cut this fundamental joint using these tools.

This Handwork department builds on the skills from my previous joinery lessons (the half-lap, the bridle joint, and the mitered bridle joint) and adds a mortise gauge and a mortise chisel. I focus on through-mortise and tenons here for two reasons. First, they’re stronger because they offer more long-grain glue surface, and the long grain of the tenon going through the stile helps the stile resist splitting. Second, your frames will more likely be flat and without twist because you mortise halfway through from both edges. Plus, through-mortise and tenons take about the same time as stopped ones.

In this example, the through-mortise is 1⁄4 in. wide by 1-3⁄4 in. long by 2-1⁄2 in. deep—a typical size for a frame-and-panel door. The rail gets the tenon and the stile is mortised.

Two helpful tools

Two tools come in handy when cutting mortise-and-tenons by hand, the mortise gauge and the mortise chisel. A mortise gauge resembles a marking gauge, but instead of one pin, it has two—one fixed and one adjustable. The gauge also has a moveable fence that, once set to the desired position, can be locked in place with a thumbscrew.

Mortise chisels excel at chopping mortises because of their stout construction. They can withstand heavy mallet blows and some levering to remove waste. Plus, the long bevel shears the wood fibers as you drive it downward—a key to mortising.