Datum feature as a pattern

[[Me...]]

How would any of you go about creating this pattern as Datum B in Calypso?

[[Ri...]]

Measure the features as either cylinders or circles inside of Calypso. Open a blank True Position Characteristic - switch to Bolt Pattern - ensure that Datum A is the Primary Datum - open up Pattern - bring in your 4 features - ensure that Translation and Rotation is turned on - name the Pattern Datum B in the top left - close the Pattern - turn on MMC.

That should be about it.

[[Me...]]

So say there was another feature with any sort of GD&T applied, can that pattern for -B- be chosen in the DRF?

[[Ri...]]

Yes, sir.

You will see it as an alignment.

[[An...]]

B(M) is the burner.

[[Ia...]]

What would the difference be between the way Richard described and Recalling those holes into one circle/cylinder feature? Just out of curiosity.

[[Ri...]]

Datum B can be used as both a Translation and Rotation datum. A best-fit circle cannot do that.

[[To...]]

I seem to recall someone on the forum describing how to create a Geometry Best Fit alignment that utilized MMC that would work for this type of application. Anyone?

[[Br...]]

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To my knowledge, Calypso can't actually handle the MMB Datum shift within a pattern like this. I think what Richard already explained is best thing you can do here.

[[An...]]

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I agree.

[[An...]]

See attached.

Contribution_08_11_2019_.pdf

[[Ri...]]

I guess I would need to do testing, but if you create a 4 hole bolt pattern, and the holes are at MMC when creating the bolt pattern, the results of the pattern should be the same as MMB now.

Like I said, I'd need to do testing, but I'm thinking that it is already doing all of this for you.

[[Br...]]

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The best fit will optimize the DRF to the 4 holes (Datum B), but what it wont do is take the collective effects of that tolerance, roll it into an Maximum Material boundary for each hole in the pattern, then allow the DRF to shift to an optimal location for the tolerance that references the [A|B(M)] Datum reference frame.

If you look at the drawing on the right in the figure posted from Y14.5, we see an MMB boundary of Ø10.1 at the true positions of each Datum feature B hole. The Ø10.1 value comes from the virtual condition of each of the datum B holes. So the MMC value (10.5) minus the position tolerance(0.4), you get a boundary of Ø10.1. So now the for the M20 holes, the DRF can shift as much as needed provided none of the surfaces of the datum B holes violate those boundaries.

So what this means with Calypso's BF bore pattern, is that it might put all those Datum B holes almost perfectly placed on their true positions, but the Position tolerance for the M20 may require them to shift in such a manner that they come almost into contact with the upper left portion of the MMB boundary. To my knowledge Calypso wont handle something this complex. Maybe there's a way with PCM. I don't know.

[[Ri...]]

Brett, thank you for the detailed explanation/clarification.

[[Br...]]

My pleasure

[[He...]]

If I'm not mistaken in the release notes for 6.8 they mention a new function where a pair of cylinders are used as a datum. Maybe that function isn't limited to a pair but it is possible with more cylinders. Someone sitting on 6.8 that can confirm?

[[Ri...]]

It is called Parallel Cylinder. It is not limited to just two Cylinders.

I did a test on the CadCube, and it built a correct cylinder (as far as I can tell).

We would need to do some testing.