Clearances and fits: preparing an assembly
How to describe a fit and inspect it before making a batch.
Describe the required movement
Should the parts move freely, fit without play, or hold by interference? State this in the brief. Include dimensions of both mating parts and mark surfaces that cannot change. A nominal CAD dimension is not a verified finished-part dimension.
Separate clearance and tolerance
Clearance specifies a difference between mating sizes; tolerance specifies permitted dimensional deviation. Record units and the inspection method. For a hole, give diameter, depth and position relative to datums. Do not choose a fit from a model image alone.
Start with a trial assembly
For printing or a new material, agree on a set of trial fits. After measuring and assembling, adjust the model, record the selected variant and then order the batch. Include the final requirements alongside the file.