DATUM SHIFT OR MMR ON DATUMS

[[Ti...]]

There is a problem with the software in my opinion when is comes to datum shift.  When you apply MMR to a cylinder similar to what is described here:

https://qualityforum.zeiss.com/topic/5042-mmc-vs-mmb/?do=findComment&comment=56526

 

If the cylinder is the only datum, the MMR application works fine. but if you apply a clocking/rotational datum as a secondary datum the software fails and says that any subsequent datums must have a material requirement size stated as well(see imaged). This is not true. You can allow for a primary datum to shift while being constrained in rotation.  If you disagree imagine hard gaging a rotor in the link above with a flat clocking side. The flat would only allow for datum shift in two directions just not rotaionally.

When I apply a MMR condition to the clocking mid plane, I still get a violation of virtual condition error.

 

I probably need to escalate this and also Zeiss inspect needs to also allow us to apply MMC conditions to non-features of size. This is a problem for us using he software everyday. PCDMIS allows for you to create bonus for a non-feature of size positional callout and you can do it in Calypso it seems:

https://qualityforum.zeiss.com/topic/21284-mmc-bonus-on-a-non-feature-of-size/#comment-121536

 

I'm not trying to yell at you guys at GOM, I just want to make you aware of what we need in the field....I need to be able to apply bonus to non-feature of sizes for terribly GDT callouts that I see everyday, and I need to be able to use datum shift when I have a clocking datum as a secondary datum. With .03mm tolerances I need all the datum shift I can get!

 

Any btw...I don't like the fact that when you use Datum shift or MMR on a datum you are required to use GDT as your measurement principle...from my understanding this re-measures the datum features using max inscribed for and ID and then Min Circum as the OD and for how small our features are this is unstable. I would prefer we can still use geometry and stick to the method we created the datum as is which I like LSQ as is.

---here is the documentation on the max ins and min circ unstable issue at hexagon:  (search for the term 'unstable')

https://docs.hexagonmi.com/pcdmis/2021.2/en/helpcenter/mergedProjects/core/geometric_tolerances/Evaluating_Size_with_the_Geometric_Tolerance_Command.htm

 

 

Edited January 21, 2025

[[Ti...]]

 

 

I just recreated this part from the ASME standard and GOM doesn't like the addition of Datum B to the AB datum reference frame. Here is a situation that you could hard gage a bore at this parts MMC size with a stop on the bottom for PLN B. Now you can jiggled that part around if the cylinder is made smaller until it is in line with the cyl A axis, and you can get the distance from datum B dialed in. But the software doesn't like this DRF setup for some reason.

[[na...]]

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Tim, I guess you tried already, sometimes Inspect wants the tertiary datum to produce result, even if not needed.

[[An...]]

This is still an issue with Zeiss Inspect 2026.

[[TI...]]

Yes it is still a problem...see below.  Datum B is a plane and cannot have a MMB material requirement.  I also don't like that you must use GDT(ASME or ISO) to measure the datum features. We use Guassian/Least Squares often from years of correlation with other methods like CMM/Vision, and also, surface quality of the mesh comes into big play when you use tangent(exterior highs) for features.  It would be like taking 7 hit points on a plane on a CMM and constructing a tangent plane...you don't know if you actually hit enough of the plane to capture the highs.  So sometimes it is prefered to use least squares.

 

[[Ma...]]

I don't know what purpose has Datum2, but avoiding it is helping. But if you need that point to set your origin, then i am out of ideas how to enable MMR on that single plane.
Point / intersection with plane and cylinder to get a point is not working also.

I understand why it needs MMR on all elements, but not sure how to enable that on single plane.