How to Cut Clean Mortises with a Router

By Premium CNC & Router Bits for Precision Cutting | Published: 2026-10-26

Category: How-to Guides

Learn the key steps to cut clean, accurate mortises using a router and a mortise bit. This guide covers setup, technique, and common mistakes to avoid.

Quick answer

To cut clean mortises with a router, use a dedicated mortise bit like the Whiteside 1302A, work in shallow passes, and secure your workpiece firmly to prevent tearout.

Why a dedicated mortise bit matters

A standard straight bit can work for mortises, but a dedicated mortise bit like the Whiteside 1302A has a short down shear flute that leaves a clean top edge. This is especially important when cutting mortises for door hinges, where a smooth top surface is visible. The 3/4-inch cut diameter is a common size for hinge mortises and tenon joints.

Trade-off: Mortise bit vs. straight bit

A mortise bit's down shear design helps prevent tearout on the top edge, but it can be more aggressive in the cut. You must take lighter passes (around 1/8 inch deep per pass) to avoid burning or bogging down the router. A straight bit is more forgiving for deeper cuts but may leave a rougher top edge.

Steps to cut a clean mortise

1. Secure the workpiece: Clamp the workpiece firmly to a stable surface. Use a fence or edge guide to keep the router path straight. A moving workpiece is the most common cause of a wobbly mortise. Test your clamping before starting the cut.
2. Set the depth of cut: Set the router bit depth to about 1/8 inch per pass. For a 3/4-inch deep mortise, this means 6 passes. Trying to cut full depth in one pass can burn the bit or cause tearout. Mark your final depth on the bit shank as a visual reference.
3. Make the first pass: Start the router, then lower the bit into the workpiece at the center of the mortise location. Move the router along the layout lines in a gentle, steady motion. Do not force the bit; let the router do the work. If the router bogs down or the bit smokes, you are cutting too deep.
4. Clear the waste in passes: After the first pass, lower the bit by another 1/8 inch and repeat. Continue until you reach the final depth. For wide mortises, make multiple passes side by side to clear the full width. Use a vacuum or brush to clear chips between passes to avoid burning.
5. Clean up the mortise walls: Once at full depth, make a light final pass along the walls to square them up. If your router bit has a bottom-cutting edge, you can also take a final pass at the bottom to flatten it. A sharp bit is essential for clean walls; dull bits cause burning.
6. Test fit the tenon: Check the fit with your tenon piece. The joint should slide together with light hand pressure. If too tight, take a very light cleanup pass on the mortise walls. If too loose, your tenon may need adjustment. It is easier to remove a little more material than to add it back.

Product facts

3/4″ Mortise Bit x 1/2″ Shank – Whiteside 1302A (AstraHP Coated): The Whiteside 1302A has a short down shear flute for a finished top edge and is recommended for cutting mortises on door hinges. This design reduces tearout on the visible top edge of the mortise, saving you time on sanding or filling.
3/4″ Mortise Bit x 1/2″ Shank – Whiteside 1302A (AstraHP Coated)