Reporting surface profile check with CMM
Reporting surface profile check with CMM
(OP)
How are surface profile measurements typically reported? The metrology lab always reports the absolute value of 2x the maximum deviation from the basic profile. In other words if the equally disposed profile tolerance zone is .010", the calculated value would be compared against .010+0" and .010-.010". They indicated this is preferential for most of their customers as opposed to reporting a positive or minus deviation from the basic profile. Can anybody comment? Is this typical?





RE: Reporting surface profile check with CMM
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RE: Reporting surface profile check with CMM
RE: Reporting surface profile check with CMM
If for instance complex outline of a seal is inspected, such information can be meaningless because it would be much more important to see/know which 'areas' of the outline are close to profile tolerance zone boundaries, which are at + and which are at - relative to true profile, which are out of the tolerance zone, etc. Having maximum deviation only would tell almost nothing in this case.
On the other hand simple YES/NO assessment might be enough, if one is only interested in checking whether the actual surface is within profile tolerance zone or not.
RE: Reporting surface profile check with CMM
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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.
RE: Reporting surface profile check with CMM
Peter Truitt
Minnesota
RE: Reporting surface profile check with CMM
The CMM operator maintains that the latter method is correct based on ASME Y14.5.1M-1994 and comparing twice the absolute deviation to the total tolerance is therefor incorrect. I've read the applicable section 6.5 of the standard, but all it does is make my head hurt. Anyone better versed in the mathematical definition standard have an opinion?
RE: Reporting surface profile check with CMM
Yes, 2X the absolute value of the maximum surface deviation is a common profile value for an equal bilateral profile. The surface deviations for each measured point are commonly negative if less material is present compared to the true profile, or positive if more material is present.
The difference between the most positive and most negative surface deviation value is not a correct way to calculate a profile value. The point of the 2* |max SurfDev| method is to find the tolerance zone thickness that will just contain the worst measured point, while keeping that tolerance zone centered about the feature's true profile. That other approach the cmm operator prdave describes yields a number of a zone that fails to stay centered on the true profile.
For Y14.45 we're working towards one method that also will work for unequal profile tolerances as well as for equal bilateral. The method also needs to work for unconstrained profile tolerances, which have no datum feature references.
Both Evan and Don Day are part of the Y14.45 effort. Either of them may have more to say about this. Whatever we have at this point may be revised before the standard is released, so it won't be much help to describe what we have so far... I just want to mention that a method that I hope will clarify profile data reporting should be available in an ASME standard fairly soon.
Dean
www.d3w-engineering.com