Identify Variation

max(group of cells)-min(group of cells) in Excel
Or, just take the highest reading minus the lowest reading, that is the variation (aka RANGE). I see "machine" variation, max of 0.0003 for ID, max of 0.0002 for all the others. If that is MM, then it is nothing, but 0.0002" is expected machine variation for 99.9999% of the CMM's out there.

Do you have Minitab?

If you are going to do one part, you could run a Type 1 Gage Study. I think for that study you would run the part 50 times to assess the bias and repeatability of your measurement device.

P-value would need to be above 0.05 and the Cg and Cgk would need to be above 1.33 to be assessed that your measurement routine and device is repeatable.

I know DAN_M had a pretty slick way of doing repeatability tests on his new programs. I think I just saw a thread about that, but not sure which one it was in.

As for tolerance, determining the Upper Spec Limit and Lower Spec Limit:

In Excel run a =STDDEV() on your column, then find the average. To determine upper spec limit (for a Cpk of 2) take the Average + STDDEV*6. To determine lower spec limit, take the Average - STDDEV*6.

If you want a tighter tolerance, then decrease the amount you multiple the STDDEV by. Multiplying the STDDEV by 3 would result in a Cpk of 1.

Matthew D. Hoedeman sorry, its in inches.
bfire85 I don't have mini tab. Trying to do things by hand in excel.

Matthew D. Hoedeman sorry, its in inches.
bfire85 I don't have mini tab. Trying to do things by hand in excel.

Maybe your company should get a license seat.

Otherwise, search Google for "Type 1 Gage Study MSA Excel". Maybe there is an example to use or possibly buy.

As another bit of advice, you should unload and reload the part between each run as well. Leaving it alone and just rerunning it will give you more consistent numbers than you will realistically see during a production run.

On your previous thread..
https://www.pcdmisforum.com/forum/pc...594-cmm-health
I gave you a Gage Correlation Document. It will get you past an auditor asking "How do you know your cmm program is accurate/yielding repeatable results?"

What if the auditor asks "How do you know your process is accurate/yielding repeatable results?"

When it comes to "Process Capability Studies", the industry standard for aerospace & medical is performing a "CPK Study".
What is cpk?
Cpk is a stats term. In your example you'd measure the diameter 30 times & record all of that data. The data gets checked for two things...
-Are all data points within tolerance?
-If all data points were chatted on a graph, how "close"/distributed are the points to eachother?
If the cpk number is above 1.33 your process is mathematically proven to yield repeatable results

At a previous role, my main responsibility was to:
-Write CMM program to measure a new medical product that was in the prototype phase
-Measure a lot of 30 pieces & output the dimensional data from those parts to minitab
-Use minitab to output a CPK study and a few other charts/graphs that bosses love to oogle at
-Present this info to management team, customers, and FDA

If you can't get minitab you can go online & find an excel form that has cpk stuff baked into it.

With the data you shared above you're like ±0.00015 on everything...they definitely shouldn't be crying unless your tolerance is crazy tight?


Hope this rant helped lol

Could that help ?
https://www.pcdmisforum.com/forum/off-topic/off-topic-aa/421577-capability-calculations-for-true-position

+/- STDDEV*3 it should be not 6. Given that following Normal destribution +/- 3*STDDEV covers 99.7% of probability.

In my company we measure 30+ times, take the standard deviation and multiply *6 and divide by the Tolerance range. If the result is lower than 10% we accept the results (repeatability results that is) with no rational. Otherwise we investigate and try to justify the dispersion.

A type 1 study uses 6 STDDEV. https://support.minitab.com/en-us/minitab/18/help-and-how-to/quality-and-process-improvement/measurement-system-analysis/how-to/gage-study/type-1-gage-study/before-you-start/example/

(it used to be 5.15 sigma, for 99% confidence interval)

Dear esteemed colleagues and degenerate operators,

Got into a fist fight this weekend performing and MSA with a 5mm X 100mm X 100mm probe scanning a 3.5 ring gage with a 90 deg wrist. Basically I was not capable until I used temp. comp and the Gage Scanning algorithm. Our tolerance was +/-.001 and final Cpk was 1.34.

Thanks.