Group of holes as a datum with modifier

[gszpot]

So I have a print that has a group of 6 holes as datum C. I understand that. But now there is a profile call out using Datum C as a tertiary datum with a modifier.
How do I construct Datum C as a feature of size so I can take advantage of the Maximum material boundary?

[LaserJay]

Is it calling the diameter of the bolt circle as the Datum?
You could create a constructed circle of the bolt pattern and put the tolerance in the nominals tab for your datum shift?

Maybe I am confused by your question.

[gszpot]

It's not a bolt circle, A random pattern of 6 holes.

[neil.challinor]

So I have a print that has a group of 6 holes as datum C. I understand that. But now there is a profile call out using Datum C as a tertiary datum with a modifier.
How do I construct Datum C as a feature of size so I can take advantage of the Maximum material boundary?

I have good news and bad news - the bad news...XactMeasure does not support patterns of holes as a tertiary datum.

The good news...The new geometric tolerance command we are about to release with 2020 R2 does.

Your holes would all need to be the same diameter and have the same size tolerance. You would need to measure all of the holes as cylinders and then dimension any size, form, position and orientation as defined on the drawing. In the DATDEF command, you would select all of the cylinders that make up your pattern and create datum C. Then using the geometric tolerance command, you could reference datum C and add a modifier if required (MMC / LMC).

The technical preview of 2020 R2 is available now (see the links on the main forum page to sign up). I strongly recommend giving it a try if you are able to. The geometric tolerance command is a vast improvement over XactMeasure which it replaces.

[Schlag]

You will not accepet bad parts leaving the "M" off from the inspection.

[neil.challinor]

No, but you might reject some parts that are actually OK. gszpot , are you able to share the drawing or the portion of it that shows the hole pattern and associated GD&T? We may be able to suggest a solution if we know exactly what we are working with.

[Schlag]

Agreed.But, if the software doesn't support it at this time whats the other option ? Without knowing the rest of the story, the .0005 shift ( " assumption " here ) you get int going to matter and why come up with some convoluted fix for that gain ? Error on the side of cation with numbers you can trust , understand and feel confident in. Using a hole pattern as a tertiary founds fishy at best .... so many possibilities and questions that could be asked on this.

[gszpot]

Sorry can't share the drawing. (Itar/aerospace) The tolerance is large enough so I will never need the bonus tolerance on this part.
Sounds like 2020R2 will have some interesting changes. Did they change the icons again too? haha

[DAN_M]

People flipped out pretty hard over the last icon change..I don't know if they're going to do that again for a while lol

[LaserJay]

Yeah I don't think they will change the icons again lol

@gszpot I would just go with not using the modifier.
I know it isn't always the best to just take the easy route or the shortcut but you are pretty limited on options here and this is the safest way to check the parts