Flatness and parallelism dependability
Flatness and parallelism dependability
(OP)
Hi,
A very simple question. Is the picture attached sensible? (Parallelism of 0.05mm for surfaces that both have 0.05mm flatness tolerance)
Either way - please try to explain why.
http://files.engineering.com/getfile.aspx?folder=c...
A very simple question. Is the picture attached sensible? (Parallelism of 0.05mm for surfaces that both have 0.05mm flatness tolerance)
Either way - please try to explain why.
http://files.engineering.com/getfile.aspx?folder=c...





RE: Flatness and parallelism dependability
If the milled surface is parallel to A within 0.05, it is already flat within 0.05 as an independant feature.
RE: Flatness and parallelism dependability
Parallelism tolerance 0.05 will inherently keep this surface flat within 0.05.
RE: Flatness and parallelism dependability
Can you explain this logic? If I define parallelism of 0.05 to a surface of flatness 0.05, won't my flatness tolerance be 0.1mm?
RE: Flatness and parallelism dependability
Parallelism is a tolerance zone of two planes .05 apart parallel to the Datum. Flatness is a tolerance zone of two planes .05 apart.
If ASME:
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Flatness and parallelism dependability
So you can specify a flatness that EXCEEDS the parallelism, if required, but if the parallelism is equal or more-constraining than the required flatness, then the flatness is redundant.
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Flatness and parallelism dependability
This will be true, only, if you use an orientation tolerance specifying a tangent plane modifier. The actual surface, then, need not conform to the orientation tolerance.
Frank
RE: Flatness and parallelism dependability
I do not understand your statement. Is not parallelism a tolerance of orientation and thus my statement is adequate? I believe specifying a tangent plane modifier would modify the statement I made but does not negate it. A tangent plane modifier would instead look at a plane resting on the peaks of the surface rather than a standard plane measurement, correct? All else would be equal? I'm not very experienced with the tangent plane modifier as I've never used it or had anyone else use it on parts I've come across.
Or maybe I misunderstand which part of my original post you disagree with.
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NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Flatness and parallelism dependability
Basically the statement that these two tolerances do not get added plus the bold text in the quote offered by JNieman pretty much clarify everything.
Putting it differently, if entire surface must fall between two parallel planes spaced 0.05 apart that are parallel to datum plane A, there is no physical possibility that the very same surface will have flatness error greater than 0.05, thus flatness tolerance 0.05 or greater does not make sense.
RE: Flatness and parallelism dependability
You said: "So you can specify a flatness that EXCEEDS the parallelism, if required, but if the parallelism is equal or more-constraining than the required flatness, then the flatness is redundant."
I believe this is the statement that Frank has objections to. And I agree with him. Nobody can forbid you to specify flatness tolerance greater than or equal to the parallelism tolerance, but there is absolutely no chance it will be ever required, because geometrically it makes no sense.
RE: Flatness and parallelism dependability
_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5
RE: Flatness and parallelism dependability
RE: Flatness and parallelism dependability
Actually I will like to get into that - in what occasions would I specify flatness tighter than parallelism? Won't that make parallelism redundant?
RE: Flatness and parallelism dependability
http://www.eng-tips.com/viewthread.cfm?qid=238967
http://www.eng-tips.com/viewthread.cfm?qid=332250
http://www.eng-tips.com/viewthread.cfm?qid=217299
http://www.eng-tips.com/viewthread.cfm?qid=314585
http://www.eng-tips.com/viewthread.cfm?qid=312392
Also, the picture that is being around for a while:
http://files.engineering.com/getfile.aspx?folder=e...
RE: Flatness and parallelism dependability
RE: Flatness and parallelism dependability
The tolerance zone is what the refinement of a parallel zone must reside within, while any additional refinement of flatness must reside within the parallel zone.