Assembly Modeling
Assembly basics
Assembly questions test whether you can position parts with mates rather than with the mouse. Know the standard mate types: coincident, parallel, perpendicular, tangent, concentric, distance, angle, and lock, plus the advanced width and path mates. Understand mate alignment - the Aligned/Anti-Aligned toggle and the Flip Mate Alignment option - because a correctly chosen mate can still place a part backwards.
Degrees of freedom
The first component placed in an assembly is fixed by default; every other component starts with six degrees of freedom, and each mate removes some. A fully defined assembly has zero degrees of freedom. Use Move Component to drag a part and watch which direction it still slides or rotates; the remaining motion tells you which mate is missing. Right-click a component to Float or Fix it, but prefer mates over Fix, since fixed components do not adapt when the design changes and are usually the wrong answer in a best-practice question.
Subassemblies and evaluation
Components can be grouped into subassemblies, patterned, mirrored, and exploded. Interference Detection and Clearance Verification check fit, and the Assembly Visualization and Mass Properties tools report on the whole structure.
Traps
Mating to a face that later changes removes the mate reference. Two mates that conflict produce an over-defined warning. A concentric mate alone leaves a pin free to slide, so a pin in a hole normally needs concentric plus coincident or distance. Mating to the wrong side of a plate flips the part, which is why alignment questions are common.
Rule of thumb
Insert the part, add one mate, and confirm the degree-of-freedom count drops before adding the next. Concentric for the axis, then coincident for the face - in that order - positions any shaft in any bore.