GD&T Question 2-17-23

[[Ri...]]

Good afternoon,

Please take a look at the attached drawing and provide feedback on the Surface Profile callout.

Is the MMB on the Primary allowed, and in conjunction with Datum B as the secondary?

GOM Inspect is not allowing me to handle this in this order - it works correctly as B A@MMB, but that's not what was on the customer's drawing.

Any and all input is greatly appreciated.

Thanks.

Edit: It appears that I have caused a lot of confusion, so I'm attaching a drawing that resembles the part a little closer.
Cone - Test - 2-20-23 Drawing.pdf

[[Ch...]]

MMB/MMC on a single plane ?

Maybe if it is a slot width..

Doesnt make sense in my book. - single plane is not a feature of size

However Im keeping an open mind as Im seeing more and more unique GDT ,,,

EDIT: I see what you mean, yes MMC on D should be doable,

If Claypso wont give it to me on Primary, I would make D primary ,and D also secondary (which normally then allows MMC), then A as teritary.

Good luck.

[[Da...]]

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Theoretically MMB on datum D is legal.

If GOM Inspect and Calypso would handle this, I haven't tried.

I also hope that on the real part you have, axis of datum feature D isn't as short as on cube example.

But datum B as secondary wouldn't change the requirement at all

[[Jo...]]

I was trying to reason thru this and here I think is the intent..

The desired outcome is the cone fits inside the counterbore, MMC makes sense in that scenario although it is insufficient to control vector. They have defined the 30° as the basic, which would seem to allow translation relative to Datum A. This was done in lieu of a gage line from Datum A, so something has to fit below flush I would guess.

My opinion is a custom DRF would be better suited, and that is a huge tolerance to allow for translation.. legal and practical aren't always the same.

customized.JPG

[[Je...]]

Drawing is incomplete. If this is a true representation of the drawing it is woefully incomplete. Datum A is a redundant control and does nothing more than Datum D. Datum D controls translation and rotation relative to its axis. Datum D controls 4 DOF. Datum A would control a 5th DOF if a basic was given to a gage line/diameter/intersection/depth etc. To ask if the MMB is applicable requires more information. While you can use MMB on Datums for a P.O.S. requirement (not MMC), the rest of the callout requires clarification.

[[Ri...]]

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Jeff, the part resembles closer to the example shown by John.

I'd love to hear more about the incompleteness.

The issue isn't if the Primary can be the Cylinder, and the Secondary the Plane. The issue is if the Primary can be the Cylinder with MMB, and the Secondary the Plane.

[[Ri...]]

I've attached a new drawing that represents the actual part closer.

Calypso/GOM Inspect perfectly handle the combination of A B (in that order). The issue is the MMB. Calypso cannot handle MMB at the moment (without workarounds). GOM Inspect allows you to toggle it on, but when you do, you get errors.

Datum A should control 4 DOF (2 rotations, and 2 translations). Datum B should control 1 DOF (the remaining translation). That should leave 1 DOF (the remaining rotation about the axis of Datum A). Without MMB on Datum A, it builds this correctly. With MMB on A it unlocks the translation that B was controlling.

I'm trying to understand if this is a GD&T issue or a software issue.

Thanks.
Cone - Test - 2-20-23 Drawing.pdf

Cone - Test - 2-20-23 Drawing.pdf

[[Ri...]]

[[Jo...]]

Richard, my interpretation of the second print is that:
Datum A constrains 2 rotations, 2 translations. The Basics of 114mm and 70° now provide a total width tolerance band oriented and located relative to Datum A, Datum B now does nothing. The tolerance band can translate infinitely down Datum A axis. The only constraint is now a 16mm distance to face to be met simultaneously. MMC on Datum A would allow translation and rotation to a minor degree of the prescribed tolerance band. So I would consider legal. We still don't understand intent.

As you know, Calypso would constrain the distance to Datum B according to CAD nominals, which maybe overly constrained to this requirement. It would also prohibit the software from allowing Datum shift on primary.

What if we envisioned this in reverse ? If the cone were the 5 d.o.f constraint and a position of Datum A feature must pass a 44.75mm rod ?

[[Ri...]]

An update to this....

It appears that Calypso 2023 handles this as long as I either use the ISO spec or if I use ASME, I have to tick "loose". According to the Calypso, with the ASME standard, it is not valid.

Either way, it works. I love you Calypso 2023.

Capture1.PNGCapture.PNG

[[Wo...]]

Got to take a look at 2023. The GDT stuff looks interesting. And CAD transparency as well!