Run Out

[[Mi...]]

When measuring RO I was taught to make Datum a Cyl and feature a Circle.

My case Its a shaft Im finding out of tolerance. Supplier using 2 cyl is finding to be in spec.

Still checking different ways but I still have the same findings

[[Cl...]]

Let me guess, you are measuring the circle way out near the end of the part?
They are measuring a cylinder, so wouldn't they get the deviation from the
origin of the cylinder, which is probably must be closer to the datum?

[[Mi...]]

Yeah thats about right.

Its a shaft, 55mm long. It has 2 larger ODs (Dat A & B) on each end of different sizes. Call out is back to an ID that is machine into Datum B side. They want RO from Dat A and Dat B.

Dat B which is the side with the ID is fine, Dat A 55mm away is not.

RO.JPG

[[De...]]

If runout is checked using a cylinder to another cylinder it will give the result of the worst runout on the measured cylinder, it should not default to giving the result at the origin of the cylinder (unless thats where the worst error happens to be).

If it is a circle being checked to a cylinder it will give the runout at the location where the circle is measured.

First thing I would check would be form error of the datum. If there is out of round / taper on the datum then evaluation settings can make a big difference.

Even on ground diameters we often see a large amount of error on runout results when using outer tangential for evaluation of the datum where switching to least squares results in an almost perfect match to plate results.

In this case the amount of distance between the datum and the feature also makes a big difference, any form error on the datum will be multiplied because of the distance between the datum and the feature.

A good compromise might be to see if they were willing to accept a check to a combined datum A-B which would likely give much more repeatable results which would actually mean something in the real world.

[[Cl...]]

We have a very similar situation/part here.
The main difference with us our print wants
position of the cylinder.

We (I) ended up measuring two circles, one
near the datum, and one farther down in X,
and reporting position 2x

[[Mi...]]

Thanks Derek. I get Form as A .014 B .022 and the ID .008
I set it up and shot a 3d line though A-B and offset to that, then made my Cyl etc. Still showing a 0.1

So much easier if that has a position callout....Ughh..