What Is Mortise Routing for Concealed Latches? (Jig Setup)
Mortise routing for a concealed latch is the controlled removal of wood for its latch body and faceplate, using a router and a latch-specific template or jig. The hardware maker’s dimensions govern the cut; there is no universal mortise size or tolerance. Measure the router setup, test it on scrap, and check code, egress, and fire-door limits before cutting.
Could you fit a concealed latch cleanly without cutting too deep, weakening the door edge, or affecting required door operation? The key is to treat the jig as a way to guide a precise cut, not as a substitute for the latch maker’s instructions. Plan the layout, check the door and opening, then make and test the cut in controlled steps.
Planning the latch, door, and jig
A mortise is a recessed pocket cut into a door edge or frame for hardware. For a concealed latch, the router usually makes two cuts: a deeper pocket for the latch body and a shallow recess for its faceplate. The latch instructions and any applicable listing set the required dimensions and limits.
Start by identifying the exact latch model and confirming its handing, body size, faceplate shape, fastener locations, and installation steps. Use the maker’s template or a jig made for that model. Do not copy a mortise size from a different latch, even if the hardware looks similar.
Check what the door is made of and where its solid edge, stile, or rail is. A narrow stile or a door with a hollow core may not have enough material for a particular latch. If the maker’s instructions do not clearly allow the installation in that door type, pause and ask the door or hardware supplier before cutting.
Measure before setting the jig
- Measure the latch body and faceplate from the hardware, not from a rough online drawing.
- Confirm the door edge width and the latch’s position relative to the door face.
- Mark the hinge side, latch side, and top of the door so the layout cannot be reversed.
- Locate nearby hinges, existing hardware, and any visible wiring or other services.
- Check the required fixing-hole size and fastener type in the instructions.
The body pocket should match the maker’s dimensions and specified depth. Add only the clearance the maker calls for. Extra room may let the latch shift or sit poorly; a tight pocket may prevent a proper fit or damage the hardware during installation.
Checking edge, frame, and egress clearances
Clearance is the space a latch and door need to fit, move, and close without binding. Check the door edge, frame, and hardware layout together before routing. Also confirm whether the opening is on an accessible route, a required egress route, or part of a fire-rated assembly.
Set the latch height and backset from its instructions and the door layout. Backset is the distance from the door edge to the latch’s operating point. Do not choose a position only because it looks balanced; the latch, strike, stile, and any existing hardware must all fit.
If the opening serves a required egress route, a concealed latch must not make escape harder. Where the adopted code applies, the 2021 International Building Code, section 1010.1.9.1, generally requires egress-side hardware to be readily openable without a key, special knowledge, or effort. Local adoption, exceptions, and the door’s use matter, so confirm the rules with the authority having jurisdiction (AHJ).
Where the 2010 ADA Standards apply, section 404.2.7 generally places operable door hardware 34 to 48 inches above the finished floor. A concealed latch still needs to meet applicable operation and egress rules. A latch that is hidden or difficult to find may not be suitable for a required accessible opening.
Fire-rated doors need a separate check. Field-routing a labeled fire door can affect its listing or violate limits under NFPA 80. Do not assume a successful fit means the door remains compliant. Check the door and hardware documentation and get AHJ approval where required before altering a labeled door.
Setting the router and cutting the mortise
A router jig holds the tool or its guide bushing on a fixed path. The cutter removes material inside that path. The gap between the guide bushing and cutter changes the finished size, so measure both and test the setup before working on the door.
For a centered guide bushing, the radial offset is:
(bushing outside diameter − cutter diameter) ÷ 2
For example, a 3/4-inch outside-diameter bushing with a 1/2-inch cutter has an offset of (3/4 − 1/2) ÷ 2, or 1/8 inch. When the bushing follows the inside edge of a template opening, the cutter runs 1/8 inch inside that edge. The exact jig layout matters, so confirm the direction of the offset rather than relying on the number alone.
Set up and test
- Clamp the jig so it cannot shift. Confirm that its opening is square to the door edge and aligned to your marks.
- Fit the correct cutter and guide bushing. Measure their diameters; do not rely only on labels.
- Set the router depth from the latch instructions. If the pocket is deep, remove material in shallow passes rather than trying to reach full depth in one cut.
- Make a test cut in scrap of similar thickness and material. Check its width, length, depth, and faceplate fit against the actual latch.
- Correct the jig or setup if the scrap cut is wrong. Do not compensate by forcing the latch into an undersized pocket.
| Cut or setup | What sets the dimension | Check before routing |
|---|---|---|
| Latch-body pocket | Manufacturer’s template and body dimensions | Test width, length, and depth on scrap |
| Faceplate recess | Actual faceplate thickness, unless instructions say otherwise | Test that the plate finishes flush |
| Guide-bushing offset | Bushing and cutter outside diameters | Calculate offset and confirm with a test cut |
| Fastener holes | Hardware instructions | Use the specified hole size and fasteners |
Route the pocket
Keep the router base flat and the guide bushing against the jig. Clear chips as needed, with the router switched off before clearing or adjusting the tool. Stay within the jig and avoid widening the pocket by hand. After routing the body pocket, check its depth and test-fit the latch without force.
Then rout the faceplate recess to the actual plate thickness unless the maker specifies another depth. Use a straightedge across the door edge to see whether the plate sits flush. Do not deepen the recess just to hide a plate that is out of position; first check jig alignment and the cut.
Fitting, operating, and inspecting the installation
A correct fit lets the latch sit as designed, fasten securely, and operate without binding. Test the latch before and after installing the door, and check that the door closes and opens as intended. A good-looking mortise alone does not prove safe or code-compliant operation.
Illustrative installation scenarios
- Interior door with a matching jig: The installer checks the latch model, measures the bushing and cutter, and cuts a scrap test. The test shows the pocket is offset, so the jig setup is corrected before the door is routed. This avoids enlarging the finished mortise to compensate.
- Narrow stile: The planned pocket leaves little material near the door edge. The installer compares the latch requirements with the door construction and stops before cutting because the maker’s documentation does not confirm that installation. A different, approved hardware choice may be needed.
- Labeled fire door: The latch appears to fit the available space, but the door is marked as fire-rated. The installer does not route it based on fit alone; they check the listing, manufacturer guidance, and AHJ requirements first.
These are practical examples, not code determinations. The door’s documentation and local requirements control.
After a successful test fit, drill only the specified fixing holes and use the specified fasteners. Ease sharp edges without enlarging the pocket. Seal exposed wood where appropriate for the door material and finish, following product instructions.
Install and adjust the latch, then check all of the following:
- The latch body is secure and does not rock in the pocket.
- The faceplate is flush as specified and does not catch on the frame.
- The latch engages and releases through repeated operation.
- The door closes without rubbing or needing unusual force.
- Egress-side release works as required for the opening.
- Any required accessibility, fire-door, and inspection conditions remain satisfied.
If the latch binds, identify the cause before removing more material. Check alignment, depth, strike position, and fasteners. Removing wood without a clear diagnosis can weaken the edge or make the hardware harder to secure.
Conclusion and FAQ
A sound concealed-latch mortise depends on the right template, a measured router setup, and a test cut. Follow the latch maker’s dimensions, verify the faceplate sits correctly, and check door construction and code requirements before routing. When the door is labeled fire-rated or serves required egress, confirm approval before altering it.
Frequently asked questions
What does mortise routing mean for a concealed latch?
It means using a router and a guide or jig to cut the latch-body pocket and, when needed, a shallow faceplate recess in a door or frame.
Is there a standard concealed-latch mortise size?
No. The latch maker’s template, body dimensions, and installation instructions set the pocket size and depth.
How do I calculate router guide-bushing offset?
Subtract the cutter diameter from the guide bushing’s outside diameter, then divide by two. Confirm the offset and its direction with a scrap test cut.
How deep should I route the latch pocket?
Use the depth specified by the hardware maker. Do not add arbitrary clearance or assume another latch’s depth will work.
Should the faceplate sit flush with the door edge?
Usually, the recess is cut to the actual faceplate thickness so it finishes flush, unless the manufacturer specifies otherwise. Check it with a straightedge and test fit.
Can I route the mortise in one deep pass?
Use shallow passes for a deep pocket and follow the router and cutter instructions. A test cut helps confirm the setup before you work on the door.
Can I route a concealed latch into a fire-rated door?
Do not assume you can. Check the door and hardware listing, applicable NFPA 80 requirements, and AHJ direction before altering a labeled fire door.
What should I do if the latch does not fit the pocket?
Stop and check the pocket dimensions, depth, jig alignment, and bushing offset. Do not force the latch or widen the cut until you know what caused the mismatch.
Can a concealed latch be used on an egress door?
Only if the installation meets the locally adopted egress rules and any applicable listing. Where the 2021 IBC provision applies, egress-side hardware must generally be readily openable without a key, special knowledge, or effort.
What height should operable door hardware be?
Where the 2010 ADA Standards apply, operable hardware is generally installed 34 to 48 inches above the finished floor. Check the applicable rules for the specific opening.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
