CLEARANCE FITS

gerald_friedman

What would be a recommended approach to dimensioning holes and pins in a model for clearance fits?

I need a more efficient way.

To date my way around this has been to use the same sketch for both hole and pin then in the drawings use +/+ tolerance for the hole and -/- tolerance for the pin.

However, this requires me to remember what the fit is supposed to be and when there are a lot of parts in a design this is hard to keep track of.

Takes me back to the days of drawing on paper.

bruce_williams

@gerald_friedman

If you are asking about model - a good way is: in part studio model one pin, Boolean subtract that with clearance offset to make one hole, and pattern faces for the remainder of holes.  Or if the locations are more random, first transform copy the pin to locations before Boolean (see the third hole from bottom left)  Then in assembly tab, mate one pin and replicate the rest.  It is best practice to model one of each part and then 'instance' any duplicates in the assembly.   Makes it easy to change and less 'overhead' (size of document).

See this example document.

mahir

For random 2D patterns you can use the Sketch Pattern FS.

gerald_friedman

Doesn't quite answer my question.

What would be a recommended approach to dimensioning holes and pins in a model for a clearance fit between the two?

mahir

Depending on the application, I either model everything with nominal dimensions (avg for symmetric tol) or max material (tightest fit). Then the tolerances are applied in the drawing. I usually choose max material since it makes it easy to visualize and measure the worst case tightest fit. Usually being too tight is a bigger problem than too loose. Again, it depends on your application. If you're trying maintain a maximum clearance instead of a minimum clearance, you might want to model everything at min material condition instead. Whatever you choose, just stay consistent in order to avoid confusion.

gerald_friedman

Mahir,

Good answer. Thanks.

Do you also model the hole and pin from separate sketches so the maximum material of each are not equal?

gerry

mahir

Correct. I size them separately. You could size them the same and then control the min clearance by offsetting surfaces, but for me that's more trouble than it's worth. Off the shelf pin sizes are pretty standard. Unless you're custom machining them, they are what they. So it's just a matter of picking the hole size to match.