What Is Concealed Hinge Mortising? (SOSS Jig)
Concealed hinge mortising is the precise routing of matching pockets in a door and jamb so a SOSS invisible hinge sits as its maker designed. The SOSS jig guides that work, but there are no universal pocket dimensions: use the current instructions for the exact hinge and jig. Then confirm swing, clearances, and any listing or code requirements before cutting.
A concealed hinge can create a clean, uninterrupted look when the door is closed. The finished result depends less on hiding the hardware than on accurate layout: pockets must align, match the hinge model, and leave enough clearance for the door to swing and latch.
I treat the jig as a model-specific routing guide, not a template that can be reused by guesswork. The hinge and jig instructions govern the setup and cuts. The door assembly, project requirements, and locally adopted codes set additional limits.
Plan the Hinge, Door, and Jamb
Start by identifying the exact SOSS hinge and jig, then check the door and frame before choosing a cut location. The pocket dimensions and setup vary by model, so the manufacturer’s current instructions are the source for the required cutter, guide, layout, and depth.
Record the hinge model, jig model, door thickness and material, jamb construction, door swing, and number of hinges required by the instructions. Also check whether the opening is fire-rated or subject to accessibility rules. Do not begin routing until you know what limits apply.
Check the door and jamb for damage, repairs, glazing, wiring, and other features that may affect routing. A door with a thin skin, hollow core, or unusual reinforcement may not provide the material needed for the specified pocket and fasteners. Do not assume that a hinge that fits physically is suitable for every door construction.
Use the model’s instructions to confirm the hinge quantity, location, edge distances, pocket size, and depth. Do not copy dimensions from a different SOSS hinge, even if it looks similar. If instructions are unclear or the door is an assembly with a listing, pause and confirm an approved preparation before cutting.
| Check before layout | What to record or confirm | Why it matters |
|---|---|---|
| Hinge and jig | Exact model numbers and current instructions | Setup and mortise details are model-specific |
| Door | Thickness, material, condition, and rating | Affects fit and whether routing is allowed |
| Jamb | Material, construction, and condition | Must support the pocket and specified fasteners |
| Opening | Swing, floor clearance, and required clear width | Determines whether the finished door works in the space |
Key next step: Gather the hinge and jig instructions, then verify the door and frame can accept the specified preparation.
Check Swing, Clearances, and Code Constraints
A correctly routed hinge can still leave a door that does not meet the project’s clearance needs. Confirm the swing and opening before cutting, and check applicable code rules for the actual building and door. Accessibility and fire-door requirements depend on the project; they are not settled by the hinge’s appearance or fit.
Mark which side the door is hinged on and the direction it must swing. Check for nearby walls, cabinets, trim, and hardware that could stop the door or restrict its use. Confirm the door’s clearances at the floor, frame, and latch side against the project requirements and the manufacturer’s instructions.
Where the 2010 ADA Standards apply, Section 404.2.3 calls for a minimum 32-inch clear opening with the door open 90 degrees. This is the clear opening, not simply the door’s nominal width. Maneuvering clearance varies by approach, latch, and closer; use Section 404.2.4 and Figure 404.2.4.1 for the relevant condition. Where applicable, operable hardware must be 34 to 48 inches above the finished floor under Section 404.2.7. Confirm which standards and code editions apply to the project.
A concealed hinge does not by itself establish compliance. The complete opening must meet applicable requirements, and the hinge must be installed as directed. If a closer, latch, or other hardware is present, include it in the clearance review.
Fire-rated openings
A fire-rated door and frame are tested and listed as an assembly. A hinge that fits a routed pocket may still be unsuitable if the hinge, preparation, fasteners, or installation method is not permitted by that assembly’s listing.
Before modifying a rated opening, check the listing and the applicable NFPA 80 requirements. Do not treat an unlisted hinge swap or new pocket as a field-approved upgrade. If you cannot verify that the proposed hinge and preparation are allowed, stop and consult the door manufacturer or a qualified fire-door professional.
Key next step: Resolve swing, clearance, accessibility, and fire-rating questions before making any cuts.
Rout the Mortises with the SOSS Jig
Mortising means cutting a shaped pocket in the door and jamb so the hinge fits as specified. The SOSS jig guides the router for the matching cuts, but the exact guide, cutter, setup, and cut depth depend on the hinge and jig model. Follow that model’s current instructions rather than a generic template or remembered measurements.
Lay out both sides. Mark hinge locations and orientation on the door and jamb using the maker’s spacing and edge-distance instructions. Transfer the layout carefully so the two pockets align when the door is hung. Check marks against the actual frame, not just the door edge.
Secure the work and jig. Support the door so it cannot tip or shift. Clamp the jig as directed, and confirm it is square and firmly seated. A small movement during routing can alter the pocket and prevent the hinge from seating correctly.
Fit the specified router setup. Install only the cutter and guide or bushing specified for that jig and hinge. Confirm that the router base is secure and that the cutter is properly held. Do not substitute a bit or bushing based on appearance or a different model’s instructions.
Test on scrap. If available, use scrap that matches the door or jamb material and thickness. Check the setup and cut before routing the finished parts. A test can reveal an incorrect setting or a poor fit without damaging the opening.
Rout the pockets. Make the cuts in the sequence and to the depth stated in the instructions. Keep the jig secure and the router controlled throughout. Clear chips as directed, and avoid removing extra material to force a hinge into place.
Check the pockets before fastening. Compare each cut with the hinge and instructions. The hinge should sit as directed, with no rocking or proud edges. If a pocket is too deep, too wide, or out of alignment, stop and assess repair options before mounting the hinge.
| Setup choice | Appropriate approach | Avoid |
|---|---|---|
| Mortise dimensions | Use the exact hinge and jig instructions | Guessing or borrowing another model’s dimensions |
| Router accessories | Use the specified cutter and guide or bushing | Substituting parts without manufacturer approval |
| Test cut | Check setup on matching scrap when possible | Making the first cut in the finished door |
| Correction | Pause and assess an out-of-spec pocket | Removing more material just to make the hinge fit |
I do not treat “flush” as permission to sand or deepen a pocket until the hinge looks right. The maker’s specified fit matters. If the hinge does not seat as directed, recheck the jig setup, orientation, and cut before proceeding.
Key next step: Verify the first pocket and setup before routing the remaining locations.
Verify Fit, Operation, and Assembly Compliance
After routing, install the hinge with the fasteners and method specified by its maker. Then test the door through its full swing and check how it meets the frame. A smooth appearance with the door closed is not enough; the hinge must move freely, and the opening must still meet project requirements.
Seat and fasten the hinge as directed. Do not force a leaf into a pocket or use a different fastener without approval. Check for a consistent fit, secure attachment, and any rubbing or binding as the door opens and closes. Confirm that the latch aligns and that the door does not strike the floor, jamb, or nearby surfaces.
If movement is stiff, first inspect alignment, pocket fit, and fastener seating. Do not assume that more routing is the right fix. Unnecessary material removal can weaken the mounting area or take the pocket beyond the manufacturer’s limits.
For an accessible opening, measure the clear width with the door at 90 degrees where the 2010 ADA Standards apply, and check the relevant maneuvering clearance and hardware height. For a fire-rated opening, confirm the installed hinge and preparation remain allowed by the assembly listing and applicable NFPA 80 requirements. Keep product instructions and any approval records with the project documents.
Illustrative installation checks
These examples show how I apply the process; they are not claims about a particular job or a substitute for product instructions.
- Interior door, ordinary residential opening: I identify the hinge and jig models, inspect the door and jamb, check the swing, and test the router setup on matching scrap. I use the specified pockets and then cycle the door to check for binding and latch alignment.
- Opening with accessibility requirements: I check the actual clear opening at 90 degrees and use the applicable maneuvering-clearance rules. I do not infer compliance from the nominal door width or from hinge placement alone.
- Rated door: I verify the permitted hinge, pocket preparation, and fasteners before routing. If the listing does not support the proposed change, I do not cut the assembly.
Key next step: Cycle the finished door, verify required clearances, and retain evidence that any rated or regulated opening remains compliant.
FAQ
These answers address common questions about concealed hinge mortising with a SOSS jig. The exact hinge and jig instructions still control the cut, while the opening’s construction and applicable rules govern whether and how the hinge may be used.
What is concealed hinge mortising?
It is cutting matching pockets in a door and jamb so a concealed hinge seats as its maker specifies and is hidden when the door is closed.
What does a SOSS jig do?
It guides a router setup for the hinge’s required mortises. Its setup is specific to the hinge and jig model; it does not make every SOSS hinge use the same pocket.
Are SOSS mortise dimensions universal?
No. Length, width, depth, layout, and router accessories depend on the exact hinge and jig. Use the current instructions for that model.
Can I use a generic concealed-hinge template?
Not as a substitute for the required SOSS jig setup. Use a generic template only if the hinge manufacturer expressly permits it for that hinge.
Should I test the setup before routing the door?
Yes, when suitable scrap is available. A test on matching material can help expose a setup or fit problem before you cut the finished door.
Can I install a concealed hinge on a fire-rated door?
Only if the hinge and preparation are permitted by the door assembly’s listing and applicable NFPA 80 requirements. Do not cut a rated door or frame based on physical fit alone.
How do I check ADA clear width?
Where the 2010 ADA Standards apply, Section 404.2.3 requires at least 32 inches of clear opening with the door open 90 degrees. Confirm project applicability and use the relevant code requirements.
What if the hinge binds after installation?
Check alignment, pocket fit, and fastener seating against the instructions. Do not deepen or widen a pocket until you know the cause and confirm the change is allowed.
Can I route an installed door?
The method depends on the jig instructions and the ability to secure and control the work. Follow the maker’s setup requirements; if the door cannot be held safely and accurately, remove it or use a qualified installer.
What should I check before finishing?
Confirm the hinge seats and fastens as specified, the door swings without binding, the latch works, required clearances remain, and any listing or accessibility conditions are met.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
