What Is Concealed Hinge Geometry? (SOSS Pivot)
A SOSS concealed hinge is a mortised, multi-link mechanism hidden when the door is closed. Its linkage guides the door through a model-specific path around a designed pivot region; it is not a universal pivot. Correct fit depends on the exact model’s template, door and frame, clearances, published capacity, and any applicable access or fire-door requirements.
A quick fix for many layout problems is to pause before routing: confirm the hinge model, then check its current template against the actual door and frame. A hinge that looks right on a drawing may still collide with trim, limit the opening, or require a preparation the frame cannot safely accept.
Selecting the SOSS model and establishing door and frame conditions
A concealed hinge’s geometry is the shape and position of its links, pivots, and mounting leaves. That geometry sets the door’s travel and the space needed for its mortises. Since SOSS models differ, there is no universal mortise size, setback, reveal, or hinge count that applies to every installation.
Before choosing a model, record the door’s height, width, thickness, and mass. Note its swing direction, frame material, stop position, and nearby walls or trim. Also identify the required clear opening and any accessibility or fire-door rules that apply.
Compare those details with the current SOSS data sheet and installation instructions for the exact model. Check the published door-size and weight limits, permitted materials, hinge quantity, spacing, and preparation dimensions. A published capacity applies to the specified model and installation; it does not prove that a weak jamb, fastener, or door edge can carry the load.
| Record before selection | Why it matters |
|---|---|
| Door size, thickness, and mass | Must fall within the exact model’s published limits |
| Handing and swing | Determines orientation and door travel |
| Frame type and condition | Affects preparation and support |
| Stop, trim, and wall positions | Can obstruct the linkage or door |
| Clear-opening requirement | May limit the usable opening angle |
| Fire or accessibility status | Adds assembly and code checks |
Treat the manufacturer’s template as the controlling layout, not a starting point for improvisation. If the door, frame, or project requirements fall outside the model’s stated limits, stop and select a suitable listed solution rather than altering the geometry.
Checking swing geometry, clear opening, and obstructions
The hinge’s motion is not a simple rotation around a visible pin. Its links move through a defined path, making the door appear to turn around a virtual pivot region. This path affects clearance at the frame, wall, floor, and trim, so check the full movement rather than only the closed position.
Use the exact model’s template or geometry drawing to trace the required preparations and motion. Mark the door face, frame stop, nearby wall, and trim on a sketch or full-size layout. Check whether the door can reach its intended open position without the linkage, door edge, or handle striking another surface.
For an opening covered by the 2010 ADA Standards, the clear width must be at least 32 in. (815 mm) with the door open 90 degrees. Measure from the face of the open door to the opposite stop, as specified in §404.2.3. Do not assume that a nominal door width guarantees this clearance.
| Check | Requirement or method |
|---|---|
| Hinge preparation | Use the selected model’s current template |
| Door travel | Check the complete swing path and intended open angle |
| ADA clear width, when applicable | At least 32 in. (815 mm) at 90 degrees |
| Floor clearance | Verify against the door, finish floor, and project needs |
| Wall and trim clearance | Confirm at closed, moving, and open positions |
A concealed hinge can change how the door approaches the frame compared with a butt hinge. Dry-check the specified geometry against the actual stop and reveal before cutting. Resolve conflicts at this stage; shifting the mortise without approval may change the intended movement or compromise the installation.
Templating, mortising, fitting, and installing the hinge
A mortise is the shaped recess that seats a hinge in the door or frame. For a SOSS hinge, both recesses must match the selected model’s template and instructions. Accurate alignment matters because the links connect the two preparations; a small layout error can cause binding or an uneven reveal.
- Confirm the layout. Verify model, handing, door orientation, template revision, and the locations of both mortises. Check measurements against the physical door and frame.
- Prepare the work. Secure the door and frame components. Use the specified routing or machining method, depth, and profile. Protect visible surfaces and keep the work square to the reference edges.
- Test-fit before fastening. Seat the hinge as directed and confirm that it fits without forcing. Move the door through its travel. The linkage should move freely, without binding or scraping.
- Fasten as specified. Use the manufacturer’s stated fastening method and a substrate suitable for the loads. Do not treat a hinge rating as a substitute for sound material around the mortise.
- Adjust and finish. Make adjustments only as the instructions allow. Keep finish, filler, and debris out of the mechanism and its moving clearances.
If the door or frame is already installed, check that there is enough access to machine both mortises accurately. Limited access is not a reason to guess at a cut. A test piece or careful mock-up may help confirm tooling and approach, but it does not replace the hinge template.
Installation scenarios: where geometry changes the decision
These examples are practical planning scenarios, not claims about named or independently documented projects. They show how to apply the same model-specific checks to different openings. The useful result is not a single “standard” dimension; it is a decision based on the door, frame, and required opening.
Interior door near a return wall. A homeowner wants a concealed hinge on a door close to a short wall return. The closed reveal looks acceptable, but the return may block the door during travel. The installer checks the model’s motion drawing against the wall position and confirms the intended open angle before routing. If the door cannot reach the required angle, the hinge choice or surrounding layout needs review.
Door in an accessible route. A builder selects a concealed hinge for a doorway where ADA clear width applies. The nominal door width is not enough to settle the question. The builder measures from the face of the door at 90 degrees to the opposite stop and checks for at least 32 in. (815 mm). If the hinge’s travel or door position reduces that opening, the assembly needs a different compliant layout.
In both cases, the geometry check happens before cutting. That order protects the door and frame from a costly, difficult-to-repair preparation.
Code, accessibility, and fire-door checks
Building requirements depend on the adopted code, the opening’s use, and the authority having jurisdiction. A concealed hinge does not remove those requirements. Confirm the complete door-and-frame installation, including the hinge, before modifying an opening that must meet accessibility or fire-protection rules.
Where the 2010 ADA Standards apply, the general maximum opening force for interior hinged doors is 5 lbf (22.2 N) under §404.2.9. That section does not assign the same 5-lbf limit to exterior hinged doors. Fire-door provisions and local rules may differ, so check the applicable requirements rather than relying on this general figure alone.
For thresholds covered by the ADA Standards, §404.2.5 generally limits the height to ½ in. (13 mm). Changes in level up to ¼ in. may be vertical; changes from ¼ to ½ in. must be beveled no steeper than 1:2 under §303.2–303.3. These limits apply to the threshold and floor condition, not to hinge geometry, but the door’s travel must still work with the finished floor.
Fire-rated openings need special care. A concealed hinge that physically fits may not be approved for a particular labeled door and frame. Confirm that the hinge, door, frame, preparation, and installation are permitted by the assembly listing and applicable NFPA 80 requirements. Concealment by itself does not establish fire-door compliance.
Verifying travel, reveal, and operation
Verification checks whether the installed hinge works as intended without compromising the opening’s requirements. Test the door through its full travel, then inspect the closed reveal, clearances, latching, fasteners, and operation. A smooth motion alone does not confirm that the door meets its capacity, accessibility, or fire-rating conditions.
With the door supported as directed, cycle it slowly from closed to the intended open position. Look for binding, rubbing, movement at the mortises, or contact with trim and floor. Confirm the latch aligns and the door closes as intended. If adjustment is needed, follow the model’s instructions rather than shifting the hinge or enlarging a mortise by guesswork.
Recheck any required accessible clear width and operating force using the applicable standard and local rules. For a fire-rated opening, verify the installation against the labeled assembly and records required for the job. Keep the model data, template, and installation instructions with project documentation.
FAQ: concealed hinge geometry and SOSS pivots
These answers summarize the main geometry and installation decisions. The exact SOSS model remains the source for preparation dimensions, capacity, and fitting instructions. Where code applies, verify the adopted requirements for the specific opening.
Is a SOSS hinge the same as a pivot hinge?
No. A SOSS invisible hinge is a concealed, multi-link hinge mortised into the door and frame. Its links guide the door through a designed path. “SOSS pivot” is sometimes used informally, but it should not be read as a generic pivot fitting or as a single fixed-axis hinge.
What does concealed hinge geometry mean?
It means the arrangement and movement of the hinge’s links, pivots, and mounting parts. That design controls how the door travels and how the hinge stays hidden when closed. It also sets the model-specific mortise shape, placement, clearances, and permitted door range.
Is there a standard SOSS mortise depth or setback?
No universal depth or setback applies to every model. Use the current template and instructions for the exact hinge selected. Transferring dimensions from another model can misalign the linkage or create a poor fit, even when the hinges look similar.
How do I choose the right SOSS model?
Compare the door’s size, thickness, and mass, plus the frame and swing, with the selected model’s published limits. Then confirm hinge quantity, spacing, preparation, and clearances using its current manufacturer data. If any required value is unclear, ask the manufacturer or a qualified installer before cutting.
Can a concealed hinge provide a 90-degree opening?
That depends on the hinge model and the surrounding construction. Check the model’s motion information and test the path against walls, trim, stops, and handles. If ADA applies, also measure the required clear width with the door open 90 degrees.
How many concealed hinges should I use?
There is no universal hinge count. Follow the exact model’s published instructions for door size, weight, and hinge spacing. The rating assumes the specified installation and sound supporting materials; it does not make an undersized or weak frame adequate.
Can I use a concealed hinge on a fire door?
Only if the complete hinge, door, frame, preparation, and installation are permitted by the labeled assembly and applicable NFPA 80 requirements. A physical fit is not proof of approval. Confirm with the listing information and the authority having jurisdiction before modifying the opening.
What is the main cause of binding?
Common causes include inaccurate or misaligned mortises, incorrect orientation, unsuitable support, and interference with the frame or nearby surfaces. Compare the work with the exact template, then inspect the full travel. Do not force the door or alter the preparation without manufacturer guidance.
How do I measure ADA clear width for this door?
Where the 2010 ADA Standards apply, open the door 90 degrees and measure from the face of the door to the opposite stop. The minimum clear width is 32 in. (815 mm) under §404.2.3. Confirm the adopted requirements and any applicable exceptions for your project.
Does a concealed hinge automatically make a door compliant?
No. The hinge is only one part of the opening. Door size, clear width, force, threshold, frame, fire rating, and installation can all affect compliance. Check the complete assembly against the applicable code, listing, manufacturer instructions, and local authority requirements.
(This article was written by one of our staff writers, Garrett Vance. Visit our Meet the Team page.)
