Understanding Mortises & Tenons in Woodworking

A "mortise" is a precisely cut hole in a piece of wood, designed to fit a corresponding "tenon" from another piece of wood, creating a strong joint called a "mortise and tenon" - essentially, you would use a mortise to securely connect two pieces of wood together, especially when you need a strong, visually appealing joint, like in furniture construction.

Important aspects include function, strength, and application

Function

"When we build, let us think that we build for ever" - John Ruskin, from Front Porch Republic

The mortise acts as a socket that receives the tenon, which is the protruding piece of wood that fits into the hole.

Strength

"Never half-ass two things, whole-ass one thing." - Ron Swanson, from GoodReads

Mortise and tenon joints are considered one of the strongest wood joinery methods due to their interlocking design.

Common applications

This joint is frequently used in making furniture like chairs, tables, and doors, where stability and a clean aesthetic are important.

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How To Cut a Mortise To cut a Mortise

To cut a mortise, first accurately mark the mortise location and dimensions on the wood using a combination square and mortise gauge, then use a chisel and mallet to carefully remove the wood within the marked lines, starting with a series of deep cuts along the mortise edges and gradually working towards the center to avoid splintering; for deeper mortises, consider pre-drilling holes with a large drill bit before chiseling out the bulk of the material.

First, Mark the Mortise

Position the workpiece: Secure the board where you want the mortise to be cut on your workbench.
Measure and mark:
- Use a combination square to mark the exact location and width of the mortise on the edge of the board.
- Set your mortise gauge to the desired depth of the mortise and scribe lines along the edge of the board to mark the mortise thickness, registering along the same registration face just in case I am off center of out of square....
- Square the lines across the board using a combination square to ensure straight edges.

Second, Pre-Drill (Optional)

Deep mortises: For deep mortises, use a large drill bit to drill a series of holes along the marked mortise area, ensuring the holes are close enough to almost connect.

Finally, Chiseling the Mortise

hand chiseling wood from a mortise — chiseling wood from a mortise

Initial cuts: With a sharp chisel, make deep cuts along the marked lines on the edges of the mortise, creating a "V" shape. Be careful not to chisel too deeply at the edges to prevent splintering.
Removing the center: radually work your way towards the center of the mortise, using a series of shallow cuts to remove the wood in layers. Use a mallet to strike the chisel for more force when needed, ensuring the chisel is positioned at a proper angle.
Cleaning up: Once the majority of the wood is removed, use a sharp chisel to refine the edges of the mortise, ensuring it is square and smooth.
Important Considerations: Sharp tools: Always use sharp chisels to prevent splintering and ensure clean cuts. Work with grain: When chiseling, work with the wood grain to avoid tear-out. Test fit: Regularly check the fit of the mortise with the tenon by dry fitting the joint before final assembly.