How to Cut Mortise Holes for Concealed Hinges: A Complete Guide

Cutting mortise holes for Concealed Hinges is a fundamental woodworking skill. Proper execution ensures a secure, flush, and professional installation. Below is a detailed step-by-step guide combining hand tools and power tools.

Required Tools and Materials

Marking and Measuring:

·Combination square

·Pointed pencil

·Utility knife (essential tool for ensuring straight edges)

·Tape measure

Cutting Tools:

·Sharp wood chisel (¾-inch or 1-inch width preferred)

·Wood mallet (or regular hammer)

·Electric drill with drill bit (for clearing debris) or Forstner bit

·Router with straight bit and edge guide (optional, improves efficiency/precision)

·Safety goggles

Installation hardware:

·Double-action hinges

·Screwdriver

·Chisel or nail (for marking screw holes)

Step-by-Step Installation Process

Step 1: Mark Hinge Positions on the Door Panel

Precision is critical here.

1. Determine installation locations: Standard installation requires the top of the upper hinge to be 5-7 inches from the top edge of the door panel, and the bottom of the lower hinge to be 5-7 inches from the bottom edge. Mark these points on the door panel edge.

2. Outline the hinge: Align the hinge flush with the marked edge of the door. Using a combination square, trace lines along the top and bottom edges of the hinge plate, ensuring the lines are perfectly perpendicular to the door edge.

3. Mark mortise depth: Position the hinge flush with the edge on the front face of the door panel. Use a utility knife to score along the side of the hinge plate, marking the mortise depth. The edge formed when the blade cuts through the wood fibers is smoother than a pencil line.

4. Determine the mortise width: Keep the hinge positioned against the door edge. Use a utility knife to deeply score the hinge outline along the door edge, applying firm pressure.

This should create a clear rectangular outline with deep grooves on the door edge, while the door panel surface will have marked depth lines.

Step 2: Cutting the Mortise

You may use a chisel, a router, or (the best approach) a combination of both.

Method A: Using a Chisel and Wooden Mallet (Traditional Approach)

1.  Mark the Side: Position the chisel vertically with the bevel facing the scrap wood block, aligning directly with the marked line. Lightly tap the chisel with the mallet to carve a vertical outline around the mortise perimeter, forming the slot walls.

2. Remove the main material: Within the mortise area, chisel a series of shallow parallel cuts along the grain, spaced about 1/4 inch apart. Do not chisel all the way through; only reach the starting depth.

3. Remove waste: Hold the chisel at a low angle with the bevel facing down, using its leverage to pry out small wood chips from between the relief cuts. Work in layers until reaching the final depth marked by the knife line.

4. Level the bottom: As you approach the marked depth, use the chisel's bevel edge facing down for precise, shallow shaving to create a level bottom. Use the hinge as a depth gauge—it should fit flush with the mortise.

Method B: Using a Router (Prioritizing Speed and Consistency)

1. Set Depth: Precisely adjust the router bit's plunge depth to match the hinge leaf thickness (typically 1/8 inch or 3 mm). Test first on scrap wood.

2. Install Guide: Use an edge guide or clamp a straight board to the door surface as a stop to align the cutter with the mortise profile.

3. Cut the mortise: Remove material in multiple shallow passes along the marked area. Never attempt to cut all material at once.

4. Finish the edges: The router will leave rounded corners. Use a chisel to square off the mortise edges (or round them) to match the hinge's edges (or rounded corners).

Step 3: Install Hinges and Mark Screw Holes

1. Test Fit: Place the hinge leaf into the mortise. Its surface should be flush with or slightly below the wood surface. If any protrusions exist, mark the high points and plane them down with a chisel.

2. Mark screw holes: Position the hinge in the mortise. Use a punch or small nail to precisely mark the center starting point for each screw hole.

3. Drill pilot holes: Remove the hinge. Drill small pilot holes at the marked points to prevent wood splitting and facilitate screw insertion.

Step 4: Repeat and Install Door Panel

1. Door Frame Tenon Groove Preparation (Stiles): This is the most critical alignment step.

·Tip: Place the door panel inside the frame, supporting the bottom with 1/8-inch shims (thick cardboard or paint stir sticks) to create an even gap.

 ·Transfer Markings: Keep the door panel closed. Precisely transfer the hinge leaf positions from the door panel to the door frame stiles.

 ·Repeat the mortise process (steps 1-3) on the door frame.

2. Secure hinges to door frame: First attach hinges to the door frame with screws.

3. Install door panel: Lift the door panel into position, aligning with the hinge blades. Insert hinge pins and tap them into place. Remove the bottom shim.

Perfectly Aligned Professional Techniques

·Visible Gap: Remember to maintain a uniform 1/8-inch gap between both hinged door panels when closed. Mortises must be cut deep enough to accommodate this gap; otherwise, the door panels will jam.

·Use Only Sharp Tools: Dull chisels compress and tear wood fibers, resulting in ragged mortise edges. Always maintain razor-sharp chisel edges.

·Corner Treatment Considerations: The shape of mortise corners (square or rounded) must match the hinge corners. Use the hinge body itself as a template.

·Exercise Caution with Deep Cuts: Wood is easier to remove than to add back. Constantly monitor cutting depth.

Common Problems & Fixes