GD&T Planes in GOM are based on ISO 5459

[[Ti...]]

I've given up on understanding on how they define planes b/c even the ASME standard uses 2d images to define their L2 constrained planes.

I just wanted to make sure my findings were correct in that the ISO standard was an external surface regardless how convoluted their thinking is. Toss an object on a surface plate and it finds 3 high points and that is your datum is my methodology.

Seems the current standard for ASME Y 14.5 2018 is the L2(whatever that means) constrained least squares...and ISO 5459 is constrained min/max, whatever that means.

If someone would like to provide clarity, I would like to see it in a 3d format.  A plane is DEFINED as 3 points non-colinear.  I don't understand how ASME and ISO represent planes in simple 2d views.

 

 

[[Mi...]]

Hi Tim,

in the current software version 2021 datum planes are constructed according to the ISO standard 5459. This means that the datum plane is established as a Chebyshev plane and the result will always be an external surface, as you said.

In the upcoming software version 2022 there will be an option in the datum system dialog to instruct the software to calculate ASME planes instead. This will also be an external surface with the requirement that the sum of squared error is minimized. We think that this is procedure is what the ASME stand wants for "L2 planes".

I hope that clarifies some of your questions.