Cumulative Axial Runout

[[Ha...]]

Does anyone have any suggestions on how to measure Total Axial Runout correctly? I'm not completely sure if there are certain filters or constraints that should be turned on within the evaluation. But, depending on the evaluation settings of the cylinder (primary datum) it makes a large difference in the results. We can make the results come out correctly, I'm just afraid we could be making adjustments that may give us false readings. I have also tried creating a 3-d line with projection points from the same cylinder, but again I'm not sure if that is cheating the results as we. Any suggestions?

[[Ow...]]

A few questions,
Are you measuring OD to OD cylinders, inner bore to bore, inner bore to OD?
All require different evaluations for different needs.
Are you scanning at least 3 sections of the cylinders?
How are you checking it otherwise that makes you question what you're getting on the CMM?

[[Ha...]]

Thank you for getting back to me, sorry I was pretty vague yesterday. The callout is .001 total runout of a plane (datum B) relative to a cylinder (datum A). We only did two sections of the cylinder because there was about .300 of surface to measure, but we will add a third. Datum A is an OD. We have not checked another way yet because it is going to be pretty difficult to rest on Datum A's surface considering there isn't much area to work with.

Total Runout.png

[[SH...]]

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In India we call it as face out( not formal), datum A is the centre axis not OD. I think it depends upon perpendicularity of plane B with respect to datum A axis and cylindricity of datum A.

[[De...]]

One problem that is likely to cause you error is that the error will be magnified due to the Datum B plane being approximately 6 times wider than Datum A is long. This means that for every 0.001 of out of square in Datum A you will see about 0.006 as runout of Datum B.

So 6 times the error is going to make this check have issues regardless.

Next thing to watch for is going to be form error on Datum A, the axis that will be used to check the runout of Datum B is going to be constructed based on your actual points, and will be based off an algorithm.

The correct method for checking runout is to use minimum feature on the feature being checked, and to use outer tangential on the datum. That said, outer tangential is notoriously bad at finding the proper axis if there is even a little form error in the datum.

This is because a few small high points can significantly impact the axis that is constructed for your cylinder, this is only magnified when your datum cylinder is significantly shorter than the face to be checked is wide.

As a sanity check you may want to add a characteristic to check the cylindricity and look at the on screen evaluation to see how the cylinder looks. Is it round? Are there high points that would alter the constructed axis?

You can also see what the difference is between Outer Tangential and LSQ to see how much of the cause is due to form.

Often you will find that LSQ gives a result more in line with a plate check than Outer Tangential will and this is generally due to form error in the datum shifting the constructed axis of the Datum.

[[Ha...]]

Thank you! Definitely explains the difference we see in our results.

Follow up question, is it good practice to call something like this out using a 3-d line instead of a cylinder? We seemed to get the same result using LSQ or if we created a 3-d line from the cylinder. (created 2 projection points: cylinder to top plane, cylinder to the bottom theoretical plane, then created 3-d line between the 2 points)- Then called out Total Runout of Datum B back to the 3-d line.

Also, the form error of the cylinder was .0002
Using LSQ or 3-d line- Total Runout was .0002
Using OTE Total Runout was .0014

[[De...]]

Since runout is a check to the datum axis I can't see any problem with it.

I think the result will still vary depending on the algorithm used on the cylindrical datum when creating your projections.

The projected points will be where Calypso expects the endpoints of the calculated datum axis are.

It is still calculating the axis because there is nothing there that can be physically measured so different algorithms for evaluation will still impact your result.

[[Ad...]]

Hey guys continuing the Cumulative Runout, I have one that the surface has to be Cumulative Axial runout to the thread.

But what I did was I did points on the thread to create a cylinder as opposed to scanning the thread. It measures .0067 even with Datum -A- bonus. The major Diameter of the thread has a .010 Tolerance Is this drawing done correctly.

My lead check this before but he used perpendicularity and the engineer said that it is okay to used.

How would I approach this to make sense of this call out?

Thanks

Cumulative Runout.jpg

[[To...]]

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I vote NO since the major diameter does very little to impact the location of the mating part. Hey, but since it's on the drawing I might take advantage of it LOL

[[An...]]

Advantage Mr. O.

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What should I do about measuring the Runout? I keep getting different results from it is way out of tolerance to it is measuring in tolerance.