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.

Some Key points about mortises include function, strength, and application.

Important aspects include

Function:

When we build, let us think that we build for ever. - John Ruskin, 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, 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.

How 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.

A Visual Demonstration:

Step By Step:

1. Layout and 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.
  • Square the lines across the board using a combination square to ensure straight edges.

2. Pre-Drilling (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.

3. Chiseling the 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: Gradually 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.

Best Woods for Mortise & Tenon Joints

Not all woods are created equal. Hardwoods generally provide stronger joints than softwoods. Here is a comparison of common woods used in joinery.

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