Help with Roundness

[[Jt...]]

part.pdf
I have these tubes that the ID. needs to be bored to size and there is no call out for roundness or concentricity, though it has a +- tolerance of .001in. The parts came in +.005 full and are out of round. Trying to figure out how to find how much out of round to see if there is enough room to clean up I.D. before contacting supplier. With a bore gage I get a reading of about .003 on one side and .0087 on other side. With CMM I scanned 6 different circles, 3 per side of tube as they are 12in long. I set all evaluation filters according to the cookbook and using LSQ. I've used roundness report and on one side it reports .0022 and other side .0065. I also used 2 point Diameter with report for max/min dimension and after comparison I get a reading of .0024 and .0092. One side seems relatively close between all readings and the other side obviously not too much. Does any one have any suggestions on how to accurately determine the I.D.'s roundness? part.pdf

[[Jo...]]

I would forget using roundess. The method of calculation isn't going to inform you of stock left. ASME rule # 1 would mean no local cross section could measure out of tolerance, and the virtual condition of the envelope (straightness) would also be controlled. By that definition, it would be a difficult requirement..

If I understand your goal. Measure the current bore with closely spaced circle paths along the length. Set the evaluation of that cylinder to be I.T.E or min. circumscribe iirc . That will tell you the diameter at which it would "clean up" by machining. The orientation to the O.D as you would hold the workpiece as a Datum, and profile will tell you min/max stock as well.

[[Ri...]]

I believe Y14.5 spells out that form is controlled by the feature tolerance if not stated.
In the op's case, roundness would be 0.002, the tolerance of the feature.

[[To...]]

Please sign in to view this quote.

I believe you meant to say Inner Tangential Element, which would be equal to Minimum Circumscribed on ID.

[[Jo...]]

Please sign in to view this quote.

thanks Tom

[[Jo...]]

Please sign in to view this quote.

Not to get off topic, but I stole this from one of Tom's post. Roundess calculation is misleading, and only part of the requirement.

toms.jpg

[[Ma...]]

I have had success using Radius Measurement to evaluate stock condition for finishing.

Constrain the circle to whichever datum structure is necessary and evaluate Radius for all of the points on the circle.

Mask this characteristic

Add Min and Max characteristics for the Radius Measurement. Then you will only output the Min and Max points to evaluate against your required finished radius.

[[Je...]]

Please sign in to view this quote.

I'm going to save this post as a great example of when Inner Tangential is useful as an evaluation method.