Assembly Constraint Conflict From Mated Holes
You are placing a pneumatic cylinder subassembly into a frame assembly. The cylinder has two mounting holes 40 mm apart on its base; the frame has matching holes but one is slotted 8 mm long to allow adjustment. You first applied a mate between the cylinder base face and the frame face, then inserted two concentric constraints between the hole pairs. Inventor reports one constraint as conflicting and the cylinder jumps 6 mm off position. The design intent is that the cylinder can slide along the slot during setup but must be locked in the running configuration. A colleague suggests deleting the second concentric constraint and using a flush constraint instead. You need the assembly to move predictably in a positional representation.
1. Explain why the second concentric constraint conflicts and evaluate the colleague's suggestion.
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The conflict arises because two concentric constraints between rigid hole pairs over-constrain the relative translation along the slot. A concentric constraint removes two translational degrees of freedom but leaves rotation and axial slide; applying two of them to holes 40 mm apart fixes the rotation as well, so the pair becomes rigid. The slotted hole was intended to allow 8 mm of adjustment, but the second concentric constraint removes exactly that freedom. Inventor resolves the redundancy by flagging one constraint and moving the component to a compromise position, which explains the 6 mm jump.
The colleague's flush suggestion is not automatically better. A flush constraint controls orientation and offset along a normal, not hole alignment; substituting it for the second concentric constraint may leave the cylinder able to rotate about the first hole, so the bolt holes no longer line up. A better fix is one concentric constraint plus a mate or flush that limits rotation without consuming the slot travel, or a single concentric plus an angle constraint set to the design orientation.
2. How would you configure the assembly so it slides during setup and locks in the running configuration?
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Use positional representations plus a controlled constraint set. Keep one concentric constraint on the round hole and one mate on the base faces. For the slotted hole, use a single concentric constraint that is suppressed in the setup representation and unsuppressed in the running representation, or use a limit constraint (Mate with limits) set from 0 to 8 mm along the slot so travel is bounded and predictable. Create two positional representations: Setup, where the slot constraint is free or limited, and Running, where the slot is locked at the chosen position by an explicit offset mate.
Verify degrees of freedom with the Assemble status or by dragging the component in each representation. Check that no constraint is flagged as redundant, and confirm that switching representations does not produce a jump. If bolts are modeled, drive their placement from the same representation so fasteners do not float. Document which representation is active in the drawing view.