extension of principles - composite profile (non-uniform)

[AndrewTT]

Can anyone tell me a reason why the attached would not be allowed by ASME Y14.5-2009?

 

[3DDave]

It isn't prevented and the rules allow it.

 

[JNieman]

I would ensure the non-uniform tolerance zone completely engulfs the tolerance zone of the second-half, however, or it'll start some interesting fights, I bet.

Say the upper frame values are
[ (PoS) | .010 (U) 0 | A | B ]

You would then have a .0025 area of uncertainty where the .005 uniform zone doesn't overlap.

I don't know if it's forbidden, but there's certainly a risk of misapplying it.


Edit: Actually I think I was wrong, as my coffee starts to kick in. Given that you've reduced the second segment to only reference a primary datum, I suppose it is likely only tolerancing form, and not location, whereas location is only controlled in the first segment. That likely works out fine in the situations I imagine applying it. I'll leave the first part of my post in case it helps discussion any. But I think I mostly just jumped the gun.

 

[mkcski]

AndrewTT:

I agree with JNieman in that since it is composite profile the lower zone is a refinement of the upper and it must lie inside the Non Uniform boundary. Us of the U symbol is recommended too

Certified Sr. GD&T Professional

 

[AndrewTT]

I think that you guys are confusing "unequally disposed profile" with "non-uniform profile". See figure 8-9 & 8-10.

 

[JNieman]

Sorry, you are absolutely correct. I should stop posting on Monday mornings.

 

[mkcski]

Woops. I fell into the trap too. Reconsidering, I think the two are compatible. The Non-U tolerance zone boundary for the upper FCF is defined by the R45 MMC and R60 LMC BASIC dimensions (or a CAD file). However, the lower frame requires a BASIC profile which the tolerance zone "follows". Referring to figure 8-9, the BASIC dimension is the R50 and the lower FCF must fall within the upper FCF.

Certified Sr. GD&T Professional

 

[pylfrm]

Can anyone tell me a reason why the attached would not be allowed by ASME Y14.5-2009?

Nothing other than para. 1.7.5.4... I wouldn't even feel the need to call it an extension of principle.

Additionally, I see no reason the lower segment tolerance zone needs to be completely contained within the upper segment non-uniform tolerance zone. In fact, since the lower segment tolerance zone is free to translate and possibly rotate relative to the upper segment non-uniform tolerance zone, you could probably get away without any overlap at all initially. I agree with JNieman that this might start some interesting fights though.


pylfrm

 

[AndrewTT]

Yes, in my mind it is not an extension of principles either. However, I called it that due to the fact that there is no example of it in the standard. Really, it is nothing more than a compound profile FCF, except that the upper tolerance zone is not a simple offset of the true profile, but something else. I expect to receive some resistance which is why I wanted some back-up from the experts here saying that it is allowed.

 

[AndrewTT]

OK, lets take it to the next level. Any reason why you could not do a compound profile tolerance with a non-uniform for the upper segment and a smaller non-uniform for the lower segment? I think this is still legit per the standard but could be confusing in showing the true profile and MMB and LMB for both non-uniform tolerance zones with basic dims (thats a lot of basic dims pointing to the same area on a print). Also, would you need to distinguish the two non-uniform tolerance zones from each other by designating them with names (i.e. non-uniform-1, non-uniform-2, or non-uniform-A, non-uniform-B)? Naming them might make distinguishing them on the print easier but the standard does not have any direction for this.