True Position MMC 2 lines of results

[[Ma...]]

Why are there 2 lines of results when dimensioning True Position with MMC in PiWeb? It looks like one is calculated without MMC and the other is calculated with MMC. Is there a way to delete or remove the one without MMC in the PiWeb report?

[[La...]]

It's not with/without MMC.

The second (M) item is the percentage of tolerance consumed, used for statistics. Because your tolerance can change with TPs with modifiers, it would be hard to evaluate the capability of that characteristic.

The second item is one you would use to evaluate that item statistically.

There is a thread in here that specifies how you could hide it if you chose, requiring modification of your report to exclude features that contain (L) or (M).

[[Jo...]]

Re: Removing .(M) from Piweb report
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by Richard Shomaker.2 » Thu May 14, 2020 8:55 am
I think there are some huge misconceptions as to what the .(M) value is. It is not your bonus tolerance. It is a percentage value of your tolerance usage. You cannot do Capability Analysis (Cpk, Ppk) on a feature that has a material modifier without converting it to a percentage of tolerance usage. If the .(M) shows out of tolerance, than your feature is out of tolerance. In addition, you cannot have coordinates for Profiles/Positions that show out of tolerance, but the feature show in specification.

I understand the frustration, I worked in a manufacturing facility for nearly 13 years, and I have had operators complain to me because the report went from one page to two pages because I added a characteristic for reference only (had no tolerance).

It's the horse and the rider problem.

If you go to Resources - Characteristics Settings Editor - Report - Transfer tolerance from the 'additional printout' option to PiWeb, you can turn off the tolerance function on the additional printout options.

For the .(M) edit your StandardProtocol doing the following:

- Open your StandardProtocol for editing
- Click on Page structure on the left hand side
- Expand Main area
- Select Protocol
- With Protocol selected click on Data provider on the left hand side
- In the Name area at the top, enter {^((?!\.\(M\)).)*$}
- Click the blue arrow to the right
- Click on Only transfer name filter

That should remove it for you.

[[Se...]]

And what happens when the tolerance is 0??? 😕

[[Ia...]]

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Then the only tolerance you have is the bonus tolerance. So the further you depart from MMC, the more (and only) tolerance you are granted.

[[Se...]]

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That´s clear. My question was concerning the 2nd line of the PiWeb report.
What happens when you try to calculate the percentage of the nominal tolerance, when the nominal is 0.
I guess you´ll always get 0 and no usable data for the capability studies... 😭

[[Ia...]]

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My bad, that is a very valid question. I wonder if they just show actuals in the negative? That'd be an interesting experiment.

[[Ri...]]

There is no issue when the base tolerance is 0.

Let assume this is an ID that you are working with and its size allowance is 60±0.1. Let's say that the reported position/concentricity is 0.05, and the reported size is 60.055.

The formula is this:

- You have to calculate the max allowable tolerance:
- Which is base tolerance + bonus tolerance
- 0 + (60.055-59.9) = 0.155
- Divide the reported position/concentricity by the max allowable tolerance:
- 0.05 / 0.155 = 0.32258
- Multiply that result by 100 to turn it into a %
- 0.3225 * 100 = 32.258%


The only issue you could potentially run into is if the ID is undersized because you wouldn't get any MMC tolerance, and your max allowable tolerance would be 0. As you cannot divide by 0 you could not use the formula above to calculate the percentage.

[[Ün...]]

When the result with a diameter tolerance of Ø32 ± 0.1 is 32.512 mm, it gives a bonus of 0.084 mm.

[[Ri...]]

MMC on an Outside Diameter is its largest allowable size. MMC on an Inside Diameter is its smallest allowable size.

For you, the formula would be the USL - Actual +0.0 (base tolerance) = total allowable tolerance.

32.6 - 32.5152 = 0.0848 + 0.0 = 0.0848 total allowable tolerance.

Actual Position divided by total allowable tolerance = percentage of tolerance usage

0.0004 / 0.0848 = 0.00472 or 0.472%

[[Se...]]

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Hi,
you´re right. The 0,00472 or 0,472% is exactly the value you should use for statistics.
But as you can see at the PiWeb report, the 2nd line (the one foreseen for statistics in PiWeb) is filled with 0´s
In this special case, the 2nd line with .(M) is useless...

[[Ri...]]

Yes, it is useless to have on the report. I don't know if it got removed in 2020, but in 2021 hopefully there will be an option to toggle it off. It is only for statistical analysis.

There is a thread floating around that shows how to remove it from the PiWeb report if wanted.