Modifier on FoS and DATUM

[[Sc...]]

Hello all,

First time posting but been lurking here for the last 8 months since I moved to a shop with Zeiss Calypso (coming from using PC-DMIS the last 10 years).

So I have a true position callout that has the MMC modifier on the Feature of Size and the primary Datum also has the MMC modifier. I can account for the MMC on the FoS but how do I handle the datum's modifier as the modifier field for the primary datum is always greyed out no matter what I do?

Attached screen shot of what I have with features and the true position field. Any help is greatly appreciated.

Scott

FOS MMC and DATUM MMC 12-5-19.png

[[De...]]

That is Datum shift, not bonus tolerance so it cannot be evaluated easily when it is a pattern being checked.

Calypso is not able to calculate Datum shift except for in very limited circumstances. Like one diameter coaxial with another directly.

As for why, assuming that print is governed by Y14.5, all three flats need to be evaluated as a simultaneous requirement.

So imagine you check the first set of flats and it would need to shift 0.0003 in Y to be in tolerance.
Now you do the second set of flats and it needs to shift -0.0001 in X for it to be in tolerance.

Evaluating them seperately could show them both good when in fact they would not meet simultaneous requirement because the required shift would potentially be different on different features.

It might be possible in this case to build something to calculate the amount of Datum shift if you wanted to put enough time into it, but the correct method for checking this is a hard gage, which it looks like it actually even lists on the print.

[[Sc...]]

Derek,

Thank you for the reply. So I used to be able to take care of Datum shift (translation and rotation) in PC-DMIS but I'm finding it lacking in Calypso. Is that why you're noting "Calypso is not able to calculate Datum shift except for in very limited circumstances. Like one diameter coaxial with another directly"? So if features are perpendicular datum shift isn't available, or doesn't work right then?

I see this a lot here (diameters coaxial with another / or coaxial with hex(flats) but as you noted with the Gage requirement on the print we usually check these with hard gaging. That's how this one was supposed to be done but someone forgot to send out a P.O. for the gage 8 weeks ago and now we're manufacturing and shipping next week (and can't wait 8 weeks for a hard gage).

Thanks for the input.

Scott

[[Ja...]]

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Scott,

Calypso cannot always compute datum displacement. Mark Ensley, with Zeiss, has stated "Calypso can only do MMC on datums that are in the same axis."
PC-DMIS "can" compute datum shift, but it's not always without bugs. There are some issues there as well, but overall it is far superior when it comes to MMB/LMB.
I would suggest, if you need to in this case, measure each planar edge of the hex. Then create intersection points at the corners, and then construct a circle out of those intersection points. Then dimension that constructed circle to your datum. It might get you where you need to be. Is it correct? No. But you don't have another way to incorporate MMB.
Or just measure without MMB if it's OK.

In a shop with Calypso and a lot of MMB/LMB you may need to start requesting more hard gaging.

[[An...]]

Far away from any standards.
See attached.

Contribution_07_12_2019_c.pdf