Scanning Spheres (Multiple sizes) for Roundness of .00005"

[[Ri...]]

I am trying to come up with a method to scan Spheres that could range from .100 to .750 (estimated range), these are ground and then lapped.

At both grind and lapped, they have to be .00005 max roundness.

Looking for speeds, filters, outliers, etc. Right now, I am using a Ø1mm stylus tip. In some cases, my results are on target with a RondCom or about .000001 to .000002 more than the Rondcom. The Rondcom typically gives results in the .00003+ to max (Its slow, cumbersome and easy for an "operator" to make a mistake, I need a better solution).

If any users have information that may be of help in this, please post, email or message me.

[[Da...]]

That's quite a tight tolerance!  What kind of CMM are you using to measure the spheres?  Are there methods you have in place to minimize your measurement uncertainty?

[[Ri...]]

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1. Micura CMM's, circa 2015. Using Calypso v2017.

2. This is information I am looking for.

[[Ri...]]

Do you really want Roundness if these are supposed to be precision spheres? 

Typically you would want to look at the entire form of the sphere. 

In the past when I've need to certify precision balls (say Grade 25 or better) I wouldn't scan it as the primary check. 

Here is an example of one that I've done before. (8) equally spaced running the direction of latitude with a single point at the north pole. 

 

Here is another example, in this example the lines run the direction of longitude. 

 

Here is an example of a 2" sphere that was requested to add the roundness at the equator. 

Edited November 17

[[Ch...]]

Hello everyone,

I would combine variants 1 and 2. I think that contains the most information and points. For a presentation/plot, you should then choose the circle that interests you most.

 

[[Ri...]]

I do use a similar scan to Richard Schomaker's first image to locate the sphere but no Center Point, the spheres have a diameter intersecting from .054-.125. and the lower portion is cut off by clearance cuts (No big deal here) so I get about 240° max scan at full center (The arc length will vary by part, it's all in PCM and Para).

I forgot to note the finish is 6Ra or less.

Also note, scanning a Ref Sphere with 0.20Mu, an MSA is in the <25% range for roundness (The sphere is Ø8mm).

The 25% is high, I am not sure if the Micura can do this, it has an MPE of 0.9.

[[Ri...]]

You are correct. While the Micura is an extremely accurate CMM, extremely tight form tolerances would push you into the Prismo Ultra world with the Form Package. 

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