ASME Y14.5 2009 Section 7.53 Coaxial Pattern of Features of Size Question

[Zach Lankton]

First Post. Quick Question Regarding ASME Y14.5 2009 Section 7.53 Coaxial Pattern of Features of Size Question
Ref Fig 7-49 & Fig 7-51

Attached is a photo of the drawing section that I am looking for opinions on.

There are 4 different size holes that are coaxial.

Section 7.5.3.3 Excerpt:
"...Where holes are of different specified sizes and the same requirements apply to all holes, a single feature control symbol, supplemented by a notation such as TWO COAXIAL HOLES is used. See Fig. 7-51. The same tolerance zone relationships apply as for Fig. 7-49."

This is well covered by Sec 7.5.3.3 & Figure 7-51 in the standard where requirements are the same for each hole.

However, in my case the requirement for one of the holes is different.

The engineer chose to use 4 composite FCF's. The intent seems clear to me that the lower segment should control coaxiality of all 4 holes, with one hole needing to be held to a tighter tolerance zone.

Figure 7-49 shows a single composite tolerance zone. My interpretation has been that the axis of the tolerance zone is established the same but the tolerance zone at this hole location is smaller.

So my question is...
Does the current drawing make this intention clear or am I totally wrong? If so, is there a better way to annotate this intention?

Thanks in advance!
Zach

 

[chez311]

First off, this question would be better placed in the Drafting Standards forum:

https://www.eng-tips.com/threadminder.cfm?pid=1103

The intent seems clear to me that the lower segment should control coaxiality of all 4 holes, with one hole needing to be held to a tighter tolerance zone.

This intent is not clear from the way it is drawn nor is it supported by the standard. The lower segment (FRTZF) of a composite control is by default not subject to simultaneous requirements - and even if sim req is specified in the FRTZF of a composite tolerance, what exactly that means is still highly ambiguous and subject to debate among GDnT experts. The way it is drawn currently you have 4x holes with an upper segment (PLTZF) that are held simultaneously to A|B|C(M) and 4x FRTZF's which are free to translate/rotate in relation to each other - they are not required to be coaxial.

The solution I think would be utilizing multiple single segment and then just add an additional position tolerance onto the hole with the tighter requirement. Unfortunately you would have no datums called out in your lower segment and it is not clear from the standard whether simultaneous requirements applies with datumless FCF's - explicitly calling out SIM REQ on the FCF's without datums may do the trick.

 

[Zach Lankton]

Thank you for your answer. My apologies on posting in this forum. I am new to this site.

 

[chez311]

No apologies necessary - I just pointed you in that direction because theres a group of really great knowledgeable people on that forum that are always willing to dig into and help with GDnT questions and issues.

Hopefully my answer made sense and the solution I proposed is viable. Also if you are controlling multiple coaxial features of different size make sure that its extremely clear which ones you are referring to - if theres other coaxial features that you are not meaning to ocntrol it could be ambiguous, a custom note could help.