Short answer: A limit mate (a distance or angle mate with minimum and maximum values) fails when the component's current position is outside the range, when the mate references measure something other than you expect, or when another mate already fixes that degree of freedom. Check the current measured value against the limits, check the reference pair and flip direction, and remove any mate that already constrains the same motion.
Steps
1. Measure the current value between the two mate references with the Measure tool. If it is outside [min, max], move the component inside the range first, or set the nominal value inside it.
2. Check the references. A face-to-face distance measures differently from an edge-to-face or point-to-face one. Use planes for predictable results.
3. Check the direction. Flip the dimension if the limit acts on the wrong side.
4. Look for conflicts. If a coincident or fixed mate already removes that motion, the limit has nothing to limit and may error. Suppress the conflicting mate.
5. For angle limits, check the reference direction and the 0° definition. An angle measured through 180° can choose an unexpected solution.
6. Test by dragging the component across the full range.
Worked example (generic)
A hinged access door should open from 0° to 100°. The angle limit mate keeps failing. The door was saved in a position measured at 120° from the frame face, which is outside the range. After moving the door to closed and changing the reference to the frame's front plane, the limit mate solves and dragging stops at the limits.
Common mistakes
- Setting limits before the component is in a valid position.
- Using curved faces as distance references.
- Combining limit mates with flexible subassemblies without testing the motion.
More steps: designing motion that solves reliably
1. Define the motion first. Write down which degree of freedom moves (rotation about a hinge axis, sliding along a rail) and its range.
2. Constrain everything else with standard mates. For a hinge, use a concentric on the hinge axis and a coincident to stop axial sliding.
3. Add exactly one limit mate for the moving degree of freedom, using plane-to-plane references for distance and plane or edge references for angle.
4. Set the current position inside the range, then set the limits.
5. Drag through the range in both directions.
6. Check interference at both limits.
Edge cases
- Angle limits that cross 180°. Angle mates measure between two directions. When the motion crosses 180°, the solver can choose the shorter way round. Choose references so the full range stays on one side, or split the motion with a different reference.
- Two limit mates on the same freedom. They over-define. Keep one.
- Limit mates in subassemblies used as rigid. The motion is frozen at the top level. Make the subassembly flexible to drag it, and accept the extra solve cost.
- Slot or path motion. For a pin in a slot, a slot mate is often clearer than a distance limit.
- Very small ranges. A limit range close to zero behaves like a fixed mate and can conflict with geometry that isn't exactly nominal.
A second worked example (generic)
A sliding drawer for a gas cabinet tray should travel along a rail, with a stop at full extension. The designer added a distance limit mate between the drawer's front face and the cabinet's front face, but the drawer jumps to the far limit whenever the assembly rebuilds. The front face of the drawer is a curved handle surface, so the distance is measured to a point that moves as the solver iterates. The designer replaces it with a limit between the drawer's front plane and the cabinet's front plane, with the current position set to closed. The drawer now stays put on rebuild and drags only within its travel.
FAQ
Can limit mates be used for interference checks?
They restrict motion. Check interference separately (Interference Detection or Collision Detection).
Do limit mates slow assemblies?
Many advanced mates add solve time. Use them where motion matters.
Is a limit mate the same as a width mate?
No. A width mate centers a component between two faces.
Can limit mates drive motion studies?
Yes, they act as limits in motion studies. Check how your study type handles contacts and limits.
Why does dragging feel sticky near a limit?
The solver is enforcing the limit along with other mates. Check for mates that fight the motion.
Should drawings show the limit positions?
If they matter for service or interference, show them with configurations or alternate position views.
Can I use a limit mate between two faces?
Yes, but planes are more stable. A curved or changing face can make the measured value jump during solving.
Do limit mates slow large assemblies?
They add solver work, especially in flexible subassemblies. Use them where motion matters, and keep the rest rigid.
How do I tell a limit problem from an over-defined problem?
Suppress the limit mate. If the error goes away and the part moves freely, the limit is the issue. If the error stays, look at the other mates.