Probe Check/Sphere Measurement Strategy

[[Ch...]]

I saw a post on here not too long ago about checking probes against an old calibrated reference sphere but I can't find it.

Basically I'm making a program to check my probes. I would like to measure a reference sphere( i'm using the one from our old CMM and still have the certificate) with different probes. Any deviations from nominal I should be able to attribute to the probe and not the sphere.

If anyone remembers this thread can you please post a link?

What is the best strategy to use for this? I wanted to use something like a helical scan on a sphere but that option doesn't appear available.

[[De...]]

I have attached a zipped copy of a program that I use for checking roundness of probes.

It does one scan around the periphery of the sphere and one over the top and reports roundness on both including a graphic element, this allows you to see the 5 most likely spots for wear on the probes.

It uses PCM to modify the scan paths based on the direction the probe faces. I was only ever written to be used on probes which are aligned with the machine axis.

If you do not have PCM you can probably remove that functionallity but it would require different programs for probes that faced different directions.

Styli Roundness Scan.zip

[[Ch...]]

Awesome,

I do have PCM. I look forward to trying this tomorrow.

[[Ch...]]

I've been trying this out and really like it, especially how it works with pretty much any probe system.

I have one question. Where did the .00508 tolerance come from?

[[De...]]

The tolerance is really just a placeholder, its 0.0002 in imperial units. It's hard to put a pass/fail value on a probe without knowing what the probe is being used for.

The point of this utility was to be able have a fairly quick check to find problems with form on a probe.

Since this was meant as a utility that can be used for any probe, a determination will always need to be made as to what is acceptable for the situation the probe is being used for.

For example, if you are checking a down probe, and the bottom of the tip has a flat spot, but that probe is only checking distances in Z, then that flat spot is probably not much of an issue.

If you have a problem with flat spots on the side of the probe and your goal is checking roundness, then your roundness error on the probe is going to have a much greater impact on your measurement.

So, the tolerance is just for reference, the real value is to be able to see numeric result and the graphic analysis. With that information, you can then make a determination from it as to how the probe error could be affecting your measurement and make a determination what if anything needs to be done about it.

[[Ch...]]

That's what I figured.

I still love the PCM that makes it work for every machine axis. I was writing one similar but I was going to end up with 5 programs, one for each axis. I will have to steal some of the ideas in this program and implement them elsewhere.

[[Ow...]]

Food for thought:
When considering what may be acceptable (tolerance wise) look at your CMM calibration reports and note that the roundness form measurement error is most likely different in each axis but, within the maximum permissible error.
However, the roundness error is verified when calibrated using an ID ring gauge, not an OD sphere so, there may be differences there too.