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Manufacturing question about circularity vs size tolerance

Manufacturing question about circularity vs size tolerance

Manufacturing question about circularity vs size tolerance

(OP)
I am in the design, but I got a question from manufacturing a few days ago. I need a bit of help to answer it correctly. Again, the main thing I don't want to provide bad information.
One of our customers supplied them (manufacturing) with a drawing which has an outside diameter (cylindrical surface) dimensioned with a size dimension as follows:
Ø .237 ±.003 with I symbol attached. (per Y14.5-2009)
Then the same OD has a cylindricity within .015 and a circularity within .008 applied.

The question from manufacturing: if the size tolerance is to be within .006 and all the actual local sizes are to be within .006 (.234 - .240) then how the circularity can be within .008. In their opinion any value bigger than the size tolerance does not make sense.

I don’t know the customer application; we are just making the parts for them per the print requirements.

RE: Manufacturing question about circularity vs size tolerance

It seems like the circularity tolerance would not do much.

RE: Manufacturing question about circularity vs size tolerance

There was a thread a few years ago that really delved into this. (What I'm about to show you was a pretty involved discussion, but if you really want an answer...)

What made the light bulb go on for me regarding circularity-bigger-than-size-tolerance was Pmarc's graphic that was the first post given on 8 May 2013:

http://www.eng-tips.com/viewthread.cfm?qid=344229

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

RE: Manufacturing question about circularity vs size tolerance

(OP)
Okay. Thank you for your help.
Crisis has been diverted. I told manufacturing to ignore the I symbol, cylindricity and the circularity callouts. They were happy with the answer. Measure the parts, as usual, actual local size and qualify the parts per rule#1 and the parts are deemed to be acceptable. Happy campers.

But I am not happy with my understanding of the I symbol, I guess.
I read the thread shown above along with other threads on eng-tips and linkedin and I found some (in my opinion) conflicting informations/conclusions regarding this subject (Independency symbol).
If independency I symbol is used and rule#1 is not in charge, and the perfect form at MMC requirement is nullified only in the axial direction (and each individual cross-section the tolerance feature still needs to have a perfect form when produced at MMC) THEN how come and why is not in conflict with the statement from Y14.5-2009
5.4.3/2009:
“The circularity tolerance must be less than the size tolerance and other geometric tolerances that affect the circularity of the feature, except for those parts subject to free-state variation or the independency principle.”


http://www.eng-tips.com/viewthread.cfm?qid=423429


RE: Manufacturing question about circularity vs size tolerance

(OP)
And to help a little bit, if possible, IF on pmarc’s sketch attached the Independency symbol is attached on Ø79.5-80.0 size dimension, will the picture pass ASME requirements?

I do have a really hard time understanding circularity, specially combined with the Independency symbol per ASME Y14.5-2009.

RE: Manufacturing question about circularity vs size tolerance

J-P Belanger, 3DDave, greenimi,or all,

Do you think that Ø60.8 “possible” value in Tec-ease example attached, is different if Independency symbol is added on Ø60.71±0.03 inside diameter dimension?
(Ø60.8 possible - bottom lower figure)

Or remain the same?--see attachment--

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