Short answer: An over-defined assembly has mates that ask for more than the geometry can satisfy at once. SOLIDWORKS flags the affected components with a "(+)" prefix and shows the mates with errors. To fix it, find the conflicting set (MateXpert helps), delete or suppress the mate that duplicates a constraint already provided, and rebuild. Don't fix it by adding more mates.
Steps
1. Read the FeatureManager. Look for components prefixed "(+)" and mates with red error icons or yellow warnings.
2. Start with the first error. Later errors are often consequences of the first one.
3. Run MateXpert (right-click the Mates folder). It identifies the mate groups that aren't satisfied.
4. Find the redundancy. Typical cases:
- two concentric mates on two holes of the same pattern when the holes aren't exactly on the same pitch;
- a coincident mate plus a distance mate on the same faces;
- a fixed component that is also mated.
5. Suppress one candidate and rebuild. If the error clears, delete it or replace it with the correct constraint. For example, replace the second concentric with a parallel mate, or with a concentric that has the rotation lock left off.
6. Rebuild with Ctrl+Q to confirm there are no remaining errors.
Worked example (generic)
A valve mounts to a plate with two screws. The designer added two concentric mates (hole to hole) and a coincident mate (face to face). The valve's hole pitch differs slightly from the plate's, so the second concentric can't be satisfied, and the valve shows "(+)". Suppressing the second concentric clears the error. The designer then adds a parallel mate between the valve side face and the plate edge to stop rotation, which fully defines the valve without conflict.
Common mistakes
- Adding more mates to "force" the component into place.
- Leaving the "(+)" state in a released assembly.
- Fixing the symptom on the wrong (later) mate.
- Ignoring a real geometry discrepancy, such as mismatched hole pitch, that should be fixed in the part.
More steps: a systematic isolation method
1. Save a copy before you start suppressing mates.
2. Collapse the problem. Open the component's mates folder (right-click the component, View Mates) to see only the mates that touch it.
3. Check what each mate removes. A coincident between two planes removes three degrees of freedom: one translation and two rotations. A concentric removes four, leaving rotation about and slide along the axis. Write down what is left after each mate. When a mate tries to remove a freedom that is already gone, and the geometry doesn't agree exactly, you get an over-defined conflict.
4. Suppress mates one at a time, starting with the most recently added, and rebuild after each one.
5. When the error clears, decide which mate expresses the design intent better and keep that one.
6. Fix the geometry if it's wrong. If the conflict comes from a real mismatch (hole pitch, face offset), correct the part. A mate workaround hides a manufacturing problem.
Edge cases
- Fixed plus mated. A component that is fixed and also has mates will over-define as soon as the mates disagree with its fixed position. Float it, then mate it.
- Mates in subassemblies. An over-defined subassembly shows its error inside the subassembly. Open it on its own to repair.
- Flexible subassemblies. A flexible subassembly whose internal mates conflict with top-level mates over-defines only at the top level. Test it rigid first.
- Patterns. Mating every instance of a pattern to a part that is already located by one instance is a classic redundancy. Use the pattern, or mate one instance.
- Tolerance-driven mismatch. CAD geometry is nominal, so a model that is over-defined only by a tiny amount still reflects a real design inconsistency. Resolve it.
A second worked example (generic)
A gas stick subassembly mates six components in a chain to a base plate. One mid-chain component was replaced with a revised model that is slightly longer, and now every component after it shows "(+)". Isolating shows that each downstream component is mated both to the previous component's end face and to a fixed distance from the plate's edge. Before the change, both relationships happened to agree. Now they conflict. The designer keeps the component-to-component mates and deletes the plate-edge distances, which matches the design intent: the stick grows with its components. After that, the replacement rebuilds cleanly.
FAQ
What do "(+)", "(-)" and "(f)" mean?
They mean over-defined, under-defined and fixed. This is standard FeatureManager notation.
Is over-defined ever acceptable?
Not in a clean released assembly. Fix it.
Does this differ from "Selected entity is not valid"?
Yes. That is a selection error during mating. Over-defined is a conflict between existing mates.
How do I count the degrees of freedom left?
A free component has six. Each mate removes some. Plan the mates so the total removed is six with no overlap.
Can MateXpert fix the error for me?
It identifies the conflicting mates. You decide which one to remove or change.
Why does an error appear only after a rebuild?
The geometry changed, so mates that used to agree now conflict.