Short answer: A coincident, concentric or distance mate has two valid solutions: aligned and anti-aligned. When geometry changes, or the solver starts from a different position, it can jump to the other solution, and the component flips. Stabilize it by setting the mate alignment explicitly, mating to reference planes and axes instead of faces that may change, and adding an orientation constraint (parallel or angle) so only one solution exists.
Steps
1. Identify the flipping mate. Edit each mate on the component and watch which one changes when you toggle its alignment.
2. Set the alignment explicitly in the mate PropertyManager (Aligned or Anti-Aligned). Don't rely on the default chosen at creation.
3. Prefer stable references. Mate to the component's main planes or axes, which don't change when features are edited.
4. Remove the ambiguity. For distance mates, set "Flip dimension" deliberately. For rotation, add a parallel, angle or second mate to fix orientation.
5. Lock where the design is final. Use a lock mate, or make a subassembly rigid, if the relationship never changes.
6. Re-test by editing the part dimension that triggered the flip and rebuilding.
Worked example (generic)
A pneumatic valve's actuator flips to point downward whenever the valve body model is updated with a new revision. The mate turns out to be a concentric between the valve port and the tube end, with free rotation, plus a coincident to a face that the update changed. The designer replaces the face mate with a coincident to the valve's top plane, adds a parallel mate between the valve front plane and the panel front, and sets the alignment explicitly. The orientation now survives updates.
Common mistakes
- Mating to faces that get re-created by part edits.
- Leaving rotation free on parts whose orientation matters (handles, actuators, gauges).
- Dragging a component to "fix" a flip instead of fixing the mate.
More steps: building flip-proof mates
1. Add reference geometry in your library parts: named planes and axes at ports, mounting faces and the main orientation (for example "Port_In_Plane," "Front_Plane").
2. Mate with those references whenever you insert the part. Face mates are fine for quick work, but library references survive part revisions.
3. Use orientation mates on purpose. For each component, decide which rotation matters (actuator up, gauge to front) and add one mate that fixes it.
4. Set alignment at creation and check it in the mate's PropertyManager before you accept.
5. Test with a geometry change. Edit a dimension that would move the mated face, rebuild, and check that nothing flips.
6. Document conventions in the CAD standard so every designer orients parts the same way.
Edge cases
- Symmetric parts. For a part that is symmetric about the mated plane, aligned and anti-aligned look identical until a non-symmetric feature, such as a port or label, is added. Set orientation early.
- Mirrored components. A mirrored component's planes are mirrored too, so alignment may need to be reversed for the mirror side.
- Configurations. A mate's alignment can't differ between configurations in some setups, but its references can be suppressed. Test each configuration.
- Replacing a component. Replace Components tries to map mate references. If the new part's faces are oriented differently, alignment can invert. Check after every replacement. The existing mates page covers the reference side.
- Coordinate system mates. Mating coordinate systems fixes all six degrees of freedom and orientation in one step where the software supports it. It's useful for library parts with well-defined origins.
A second worked example (generic)
Two identical gas sticks are placed side by side, one mirrored. After a regulator revision, the regulator knobs on the mirrored stick point to the back. The mirrored stick's regulator mates were created by mirroring and inherited the alignment from the original stick, and the revision changed which face was used. The designer remakes the regulator mates on the mirrored stick with the regulator's front plane and the panel's front plane, with the alignment set explicitly. Now both sticks keep their knobs to the front after the next revision.
FAQ
Is this the same as a lost reference?
No. The mate still exists and solves. It just picks the other solution.
Do SmartMates cause flips?
They can, because alignment is inferred from where you drop the part. Check alignment after SmartMating.
Does this matter for automation?
Yes. Generated assemblies should set the orientation explicitly so a rebuild doesn't change the design.
Are plane mates slower than face mates?
Not meaningfully, in typical assemblies. Stability is the main benefit.
Can I lock orientation without fully defining position?
Yes. A parallel or angle mate fixes rotation and leaves the translations free.
What about lock mates?
They fix two components together completely. Use them for relationships that never change, but they hide intent.
How do I find which mate flipped?
Look at the mates folder for the component, and flip-test each candidate. The one that restores the correct orientation is the one to rebuild with stable references.
Will a fully defined part ever flip?
It can, if the geometry under a mate changes and the solver finds a different valid solution. Stable references reduce this.