roundness
 

roundness
hi,
i am measuring a large diameter of 100mm on a cmm. the tolerance on the interal diameter is extremely tight +/- 0.05mm. a lot of my measurements have had roundness values greater then the tolerance range > 0.1 which i have considered to be out of spec. is this correct? also, some have roundness values less then the tolerance range, like 0.09 for example, but the nominal reported by by the cmm is at or just below the lmc of 100.05mm. would this be considered in spec? it seems to me that not likely within the size limits in this senerio. my measurement experience is limited and there is no meteorologist in house. if anyone could explain how to interpt such results or suggest another approach it would be appreciated.
the roundness (circulatiry in asme) tolerance zone is defined by two concentric circles offset by the total tolerance called out. so if your tolerance callout says ±0.05 mm that means that all circular elements of your part must lie within a band of 0.05 mm. a reading of .1 mm or higher is at least twice your allowed tolerance for the part. is that the answer to your question?
"...roundness (circularity in asme) tolerance..."
not circulatiry.
and from my understanding of cmm's, from your first touched point on the part, with your tolerance callout, you shouldn't see any delta greater than 0.025 mm.
ok, now i'm done. :)
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