Adding MMC to Position Characteristic

[[Ra...]]

See attached. The alignment is symmetry plane of -A- and -B- and then -C- point tertiary. Question I have have is how to get the MMC into the True postion characteristic for -A- (11.6 width) and -B- (16.2 width) regarding the 9.4mm thru hole? I currently have the symmetry of -A- plane as primary and symmetry of -B- plane as secondary.  MMC is not an option in the characteristic with the symmetry plane alignment. Thanks!

 

 

[[Cl...]]

Constructing a Symmetry plane should allow you to us MMC.

[[Jo...]]

The Symmetry plane does allow MMC if it is the feature for evaluation, but the software doesn't allow MMB on the DRF. 

I'm not even sure MMB on Datum A would even do anything since it is parallel to the axis of the bore. 

 

 

[[Ra...]]

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Yeah I was a little puzzled at the GD&T in that regard

[[Jo...]]

I thought I had a workaround for you that I had seen before, but the software still doesn't allow it. 

The workaround was to create a perpendicular for each datum, then create two theoretical circle features and use PCM to right-click on the diameter box and add the get actual for the length of the perpendiculars. 

The thought was that it would allow you to add the modifiers to the circles, but it is still grayed out 😞

[[Ch...]]

if I had to absolutely do this, I would end up creating a theoretical cylinder for -A- with data that matches the symmetry plane, and probably require a best fit position to get MMC of A, I think I have done it a few times actually.

[[Ch...]]

Id be curious if this works with symmetry plane MMC/MMB with the 2025 GDT Engine

[[Ri...]]

Yes

[[Ro...]]

Why not use a formula for the MMB?  Take -A- width and -B- width for use in the formula.

[[Ri...]]

Because that's not how MMB/LMB works. 

 

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[[Ma...]]

That's something i'll try on monday.

Symmetry plane should give MMB - constructed symmetry from planes won't.

[[Pa...]]

Came here to say what Martin and Richard said.

The last programmer we had here worked 12 years in Calypso and did not know that symmetry planes could be constructed directly without point recall.

Every manager needs to be reminded the difference between MMC and MMB so they can roll their eyes monthly.

[[Ra...]]

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I did measure the symmetry planes within the features/special geometries (not constructed) and toleranced the -A- & -B- distances 11.6 and 16.2 distances given for each. When I recalled the planes for spatial and planar alignments to report TP of one of the Ø9.4 cylinders, there was not an option for MMB. Using older 6.6 version Calypso 2018. Most likely approaching incorrectly but that's why I'm here. 🤷‍♂️

[[Ma...]]

Well - on our Calypso 7.8 ( 2024 ) it can not make MMB on those symmetry planes, but using GD&T it's possible to use that.

[[Te...]]

The Symmetry Plane in Features/Special Geometries/Symmetry Plane is a feature of size it understands ID or OD and should allow you to use MMB / MMR

Cannot use the constructed Symmetry 

The New GD&T engine in 2025 should allow MMB/R more then the old engine

A and B are widths so they are allowed bonus (shift)

Works in the new GD&T engine  

[[Pa...]]

I'd test this before sending it:

Set up your position char (legacy) as a pattern evaluation with only one feature in your pattern.  From the best fit window select "view tolerance".  Now back out in the Char definition I believe you'll be able to select MMB.  

I don't claim to know if this produces favorable results.  I just noticed once by accident that where I cannot select MMB, using "view tolerance" makes it so I can.

Have not tried incorporating symmetry planes.