Runout/concentricity of a cone

[[Da...]]

Here we go again...

I have a small ID cylinder. I have a very small chamfer below it. ID is .375 and about .400 long. the chamfer is on a shoulder about .230 below the cylinder. The chamfer is 45 degree per side and has an end opening of .250. I check the chamfer with a cone feature using 2 circles. So, for runout I can use the cone itself, or the shell intersection of cone and adjacent face. The results don't look very good both surfaces are ground in one chucking, and it should be concentric W/I .0001 or less. I am getting values at .00025/.0005.
So, I found that a 9mm probe will contact the cone tangent right in the middle of the conical surface!!! I used a self-centering point to pick up the cone and used its X and Y coordinates (formula) for a theoretical circle and asked for run out. The SC point looks worse, but it's much more consistent than the cones intersect numbers. Is there a better way to do this? Both are not showing a believable number.

[[Ma...]]

I am not familiar with those numbers so i can not tell if is cone big enough, but if a problem is to have right touch spot i would use curve and alignment from curves to help with that if curve is available.

[[Da...]]

Here ya go Martin, I converted for you 🙂

I have a small ID cylinder. I have a very small chamfer below it. ID is 9.5 mm and about 10.1 mm long. the chamfer is on a shoulder about 5.8 mm below the cylinder. The chamfer is 45 degree per side and has an end opening of 6.3 mm. I check the chamfer with a cone feature using 2 circles. So, for runout I can use the cone itself, or the shell intersection of cone and adjacent face. The results don't look very good both surfaces are ground in one chucking, and it should be concentric W/I 0.0025 mm or less. I am getting values at .006/.012 mm
So, I found that a 9mm probe will contact the cone tangent right in the middle of the conical surface!!! I used a self-centering point to pick up the cone and used its X and Y coordinates (formula) for a theoretical circle and asked for run out. The SC point looks worse, but it's much more consistent than the cones intersect numbers. Is there a better way to do this? Both are not showing a believable number.

[[Ri...]]

My bet would be on your datum more than the feature. Remember that Calypso has to calculate the axis of the datum, and then project it to the feature. The more uncertainty in your axis the more uncertainty in the GD&T calculations due to projection error.

Can you use a plane that the datum cylinder is perpendicular to as the Primary Datum, and then the datum cylinder as the Secondary Datum to see if it improves the results to something that makes more logical sense?

[[Ma...]]

Thanks for conversion 😉

If it's turned part, then it can be deformed by clamping.
Wouldn't be enough just circle instead of cone? Is there total runout or just runout? When cone/cylinder is short, then it can result in incorrect A1/A2.

Machining strategy can also make a little deviations on surface so results can not be as thought.

Sketch would be helpfull if possible - with addiction of probe radius.

[[Da...]]

I use the inner plane to establish Z and program the cones height based on that Z location (minus a bit). Otherwise, the rest of the part is turned, the part is heat treated so, we consider no other planes square or consistent. The 9.5 X10.1 cylinder is used as the alignment (2 circles recalled to a 3d line). A mating piece is inserted in the bore and has to seal on the small chamfer. So, all R/o and alignment is back to itself. Does that make sense? The parts are chucked in a very precise Northfield chuck , then both the cylinder and the chamfer are ground at the same time. We have no way of testing this r/o off the CMM. but the amount of r/o is not really possible (since they are ground in one chucking).

We have put an indicator on the chamfer before removing it from the chuck, and it checks less than .0001 total (.00254 mm)
The customer wants an inspection report from the CMM to verify. We also run quite a few in process checks during production.

[[Ri...]]

I still think your datum length is most likely the culprit.

I guess the other question is if you are seeing roundness or position (maybe both) error in the form plot for the runout. If it is roundness, it is possible that the part is being distorted from clamping which is why it would show good clamped. If it is position, then it is most likely your datum not being robust enough.

[[Da...]]

Please sign in to view this quote.

I Hear Ya !
I've tried a few things and now I'm even more confused. Roundness is around .000036 on the cylinder. I changed the alignment to a 4-circle cylinder and spread them out as much as I can. But, if I open the cone it shows actual X and Y being out .0013 and .0002 then if I ask for the runout of the cone, I get .00014. What is it checking????