GD&T CALL OUT

[[Re...]]

Could any of you gd&t experts tell me if this is a valid call out.

Untitled.jpg

[[Me...]]

Looks legit. Can't tell if -B- is a width or a diameter but it doesn't really matter. Level and origin to -B-, origin to -A- , and clock to -E-. Might be tough to create tangent circles from the spline to get -E-. Maybe you could use a self centering point and use a probe size as close to the diameter noted for -E- as possible.

Robert

[[Re...]]

Hey Robert thanks for the reply. The program is done just as you have described, however when establishing that datum reference frame in Calypso, there is no ability to add the modifiers for datum B & A.

[[Me...]]

-B- needs no modifier. It's regardless of feature size. If you're checking the holes as a bore pattern it won't allow MMC on -A-. Try reporting their position separately.

Robert

[[Ja...]]

I would argue that you should not report position separately. If it is a bore pattern, report it as such. Calypso will do it's best to simulate the material boundary that is called out.

In general, I have learned that Calypso cannot handle Max Material on a datum (MMB).

[[Me...]]

You're correct, Jacob. Good catch!!! -A- can't provide datum mobility in multiple directions at the same time for each hole. Best to disregard the MMC on -A-. It's probably not much anyway on the spline ID.

Robert

[[Za...]]

Please sign in to view this quote.

This is poor advice & incorrect.

While Datum Shift for Datum Feature -A- MAY be negligible, it technically allows for it.

You would want to create a BF Alignment

Please sign in to view this quote.

This is also incorrect & the last 2 sentences contradict each other.

Calypso doesn't just 'do it's best' to calculate Datum Shift, you have to specify that it does.

Calypso can absolutely properly calculate Datum shift

[[Ja...]]

Zach, any geometric tolerances sharing a DRF must be evaluated simultaneously per ASME. So I am correct when I say that the Position should not be reported separately but rather as a pattern. Do you agree?

Furthermore, I used the words "in general" to imply a general case, i.e. it cannot always handle material boundary modifiers; not that it always cannot. See?
Sure it can in this case, being a bore pattern. That was the first part of my "contradictory" response. Calypso can handle it in one other case, that being coaxial features. If a feature is called out to a coaxial datum, Calypso can handle material boundary modifiers. If you have heard otherwise, I'd like to see your source. Zeiss themselves told me these were the only two cases. If you have not heard otherwise, do you agree?

Those were the only two points that I made in my response. No poor advice, nothing incorrect. Just not as spelled out as the response that you have provided.

Also, I will defend, slightly sarcastically, that Calypso does 'do it's best' to simulate material boundary condition. After all, the algorithms that perform the computations come from a background in optimization...

[[Re...]]

Thanks for all of the replies. Engineering is contemplating on changing the call out.

[[Me...]]

Please sign in to view this quote.

Thanks for the feedback, Zach. I noticed you changed the Best Fit type to allow for MMC on the Datum.

So if the holes are fully constrained by the datums then there is no Best Fit, meaning you can't tick any of the boxes in the BF section. Just mobility depending on the datum size. Is that correct?

Can you point out where Calypso shows the amount of shift that's being applied in the True Position characteristic?

Robert

[[Za...]]

Please sign in to view this quote.

Position & Profile FCFs that are called back to the same datums, in the same precedence, at the same boundary conditions do fall under simultaneous requirements. So yes, I do agree that they should not be evaluated separately.

Unless i'm misunderstanding your 2nd paragraph, I don't really agree. To use the BF your features do not have to be a bore pattern. In my experience they do not have to be coaxial either. You can BF a single feature if you need to apply any Datum shift. Now if you have say 2 different bore patterns on perpendicular faces then you might run into cases where the pattern perpendicular to the DRF may not effect the shift that much.(one set would be on different axes once it is reported in a different characteristic with special functions applied)

Personally I would recommend using a BF for all mobile reference frames

Please sign in to view this quote.

Robert, Yes I agree the DRF is fully constrained. All 6 degrees are constrained. The 'mobility' in this situation would be the MMB on Datum Feature A.

You can see any shift applied in the area marked in the screenshot shown below

[[Me...]]

Hi Zach,
Here's the part I don't understand. If I choose BF Bore Pattern, choose 3 Datums that fully constrain the geometry, and choose Gauss, I can still choose BF and release DOF, even though the geometry doesn't allow any. So using Gauss or one of the other methods without references, Calypso ignores the constraints of the datum features. So I have to decide based on the print what DOF to release because Calypso doesn't know what to do.

However, if I choose View Tolerances as my fitting method for MMC/LMC, I need to check all the boxes to get any datum mobility and it's doing no BF other than using that datum mobility? It's not doing any other BF calculations like using Gauss, etc?

That's what I don't get. The 2 behaviors are the opposite of each other in the same dialogue box. And there is no documentation that I can find that describes any of this in depth.

Hope that made sense. Thanks for your help. Just trying to understand this silly software.

Robert

[[Za...]]

If you want to use a modifier on a datum feature you have to choose the 'view tolerance' fitting method.

If you have a DOF that is free & no MMB, say just rotation around Z axis, you can use Gauss.

So for the part that started this thread you would set the Datums as B|Am|E, Fitting Method would be View Tolerance, with the Translation boxes ticked and the Rotation Box UN-ticked(*when you untick the Rotation box you should see 2 Translation boxes, one for each axis)

By doing it the above mentioned way, the DRF would only shift within the allowances of the MMB on Datum A. NOT completely unconstrain 2 degrees of freedom

[[An...]]

I had a question related to this. In the original post both call outs were to the same DRF. What if the DRF is different? For example, I have three callouts. The first callout is for datum C which has an MMC on just datum B. The next call out adds in datum C with an MMC. This callout is for a pair of bolt holes in a pattern with Datum C. The last callout is a surface profile callout to Datums A and B with an MMC for basically the outer most diameter of the part. Because there is an MMC on Datum B (a cylinder) on all three callouts, they would have to be evaluated simultaneously correct? Based on Zach's walk through, the call out and the DRF would have to be the same for all the features considered. Is there a way to evaluate the FCF's in my example?
Thanks!

datum shift ex.pdf