TP of hole Pattern

[[Jo...]]

Hey Everyone, 

Just need to double-check my work on the true position of a hole pattern to a single datum. Do these need to be measured as cylinders or is circle on a cylinder allowed?

Here is my characteristic with redacted info. 

Here is a mockup drawing. 

 

Appreciate the help!

[[Ra...]]

I would probably measure as cylinders and intersect with the OD. If you measure as circles, then the "depth" at which it is measured plays a huge role in it's position evaluation. If the part isn't machined really close to perfect, I could see it becoming an issue.

I'd also consider changing the coordinates to polar.

What Calypso version are you on? I'm not sure how the best fit handles a pattern where the axis of the features are not parallel/perpendicular to the primary datum.

[[Jo...]]

Thanks for the feedback 

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 yeah that makes sense for sure. I will give it a shot. 

I am using Calypso 2021 (7.2).

[[Ri...]]

You cannot use the old GD&T Bore Pattern Best Fit for holes that are perpendicular to the axis of rotation - it will only truly work (with a pattern at least) if they are parallel to the axis of rotation. 

As long as you don't need any MMB/LMB evaluation - I would first use Geometry Best-Fit to the DRF (allow rotation), then evaluate the Position of each cylinder back to the Geometry Best-Fit - you will need to either use the Polar evaluation or the Special Rotation to align the axis for each hole. 

[[Jo...]]

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That makes sense why Randawggs suggestion of using the intersection of the axis to the od worked for me

[[Ri...]]

That will cause issues though because since it is a point you are evaluating all three axis. The hole position should only be constraining its rotational angle, and the height location.