True position applied to a thickness

[dcoss]

I have cylindrical shaped part with three fins around the diameter, equally spaced. See FCF:image.pngI am taking a point on each side of each fin to determine the .079-.118 thickness, then creating a midpoint between the two points. Then I used the midpoint to do the true position, but since it is a point, I can't take advantage of the MMC. I can probably have PC-DMIS put on the thickness on the report and then calculate bonus manually and subtract that from the true position on the report. But is there a way to have PC-DMIS do this so that it can take the thickness and then calculate bonus and apply it to true position?

[JacobCheverie]

You can construct a (probably 1D) width from your points and you should be able to use MMC.

[DeWain Hodge]

You can construct a width and position the width and get your MMC, but position of a width doen't work if you are using legacy tolerancing. If you use legacy you can construct a generic circle from your mid-point and width and get your bonus in legacy.

[neil.challinor]

This method would still not be quite right because it would only allow you to dimension each fin individually whereas the requirement is for them to be considered simultaneously as a pattern to the A|C datum reference frame. Depending on what datum A and C are, you would need to align to them - possibly including an element of best-fitting if A|C is partially constrained - and you would then also need to include an additional weighted best-fit alignment, rotate only, on the three widths to allow for the MMC.

Much easier to use the Geometric Tolerance command and let the software do all the hard work for you.

[neil.challinor]

You need to construct three widths (one for each fin) and then use the geometric tolerance command to report position of all three of them as a pattern to datums A and C.

[Mike Ruff]

As a side note, bonus is added to the true position tolerance, it is not subtracted from the measured value.

[ALousyUser]

Mike is right. See thread: https://www.pcdmisforum.com/forum/pc...ng-if-function

[mrollings53]

According to his profile he is running 2015.1. Will Xact Measure handle this as well?

Machine Type
DEA Advantage Silver
Software Version
2015.1

[neil.challinor]

Yes, but he may need to construct a set from the three width features (can't remember if that was required for patterns in general or if it was only needed when referencing a pattern as a datum).

[dcoss]

According to his profile he is running 2015.1. Will Xact Measure handle this as well?

Machine Type
DEA Advantage Silver
Software Version
2015.1

We're running 2021.2 now. I guess I should change that on my profile.