special element symmetry plane as a secondary datum

[[Sv...]]

Hello,

I have a problem with the special element symmetry plane (2x parallel planes, with minimum inscribed condition -> see feature of size as datum ISO5459). The single evaluation works so far. However, if I want to use it in a coordinate system as a secondary datum (additional constrain of the direction by a primary datum) it automatically switches to gauss element.

My basic procedure in Calypso 7.6.2009:
-the body is a cube and I want to have the support surface as primary datum
-the constrained symmetry plane (see above) of two parallel planes form the secondary datum and the constrained symmetry of the other form the tertiary datum
-Datum according to ISO5459 so the CS is in the middle of the primary datum plane
-The planes are all measured individually via a grid and the symmetrical one is formed via point recall using the special element symmetry plane

Does anyone have an idea why this is the case?

[[Ha...]]

If I am understanding correctly, you are using a secondary alignment for a characteristic.

If that is the case, you will need to change the evaluation of the feature inside the alignment in order to evaluate it as a maximum inscribed element even if the global settings have the outer tangential element selected for the form datum options.

[[Sv...]]

Hello Mr. Harter,

this is not a datum system for a special caracteristic, but it is my main datum system for a scientific study (so nothing functional and gaiussian would not fit optimal).

-datum A (primary): base plane of the cube (ISO5459 with A[CE])
-datum B (secondary): feature of size of two parallel side planes (ISO5459 with B[X], with the constrains perpendicular to A, size is variable)
-datum C (tertiary): feature of size of the other parallel side planes (ISO5459 with C[X], with the constrains perpendicular to A and B, size is variable)
-datum system: A[CE],B[X],C[X]

If I now want to build up a CS here, it changes both [X]s to [G] (see German appendix of the working protocol). reason: check probing strategy / number of points! (there its outer but its th same with inner tang.-plane), lets ignore that [X],[CI] or [TI] is in Calypso the same)

I have 2 “identical” opposing grids with slightly more than 450 points each. Gaussian works.... So the software can calculate something.
If I now want to evaluate these symmetry planes dimensionally (using directly the features), it works with [X]/[TI] etc. even if I also lock the normal vector.

Could it simply be that the constrains parallel and additionally perpendicular to A are not yet correctly implemented in my version 7.6.2009?

Edited June 25, 2025

[[na...]]

Please sign in to view this quote.

I just wanted to break down symbols, as they are fairly new, correct me if I'm wrong. From ISO 5459:2024, paragraph 8.2.3:

CE means Chebyshev (Minimax) External, this was the default in ISO 5459:2011 and it's not anymore,

CI means Chebyshev (Minimax) Internal,

G means Gaussian, maybe it should be written as GM, or M can be omitted?

X means Maximum Inscribed, maybe it should be written as XM, or M can be omitted?

What does T in TI mean?

 

[[Sv...]]

Please sign in to view this quote.

So for the X the material condition is kind of in the algorithm of the maximum inscribed element (the counterpart is N), My opinion is that for a hole X and XM(no condition) and XE(external) or X+(moved to the most outsided point of the material) will be the same because it´s an S(max)-function. For a shaft  it´s X = XI = X-. So X and N is only for feature of size, C and G are L-functions wich are available for all.

Actually you can ignore the T because I just use it internal.

The T is the tangent feature of the ISO1101 (ass. for the toleranced feature) and its not in the ISO5459 or ISO4351. Refere to ISO1101 it´s a L2-const. external on the convex hull.

[[Te...]]

If a width is the Datum use Features/Special Geometries/Symmetry Plane and the recall feature points of the 2 planes.  

This Symmetry Plane is a Feature of size with OD or ID which should be evaluated correctly and allow MMR(B) if required

[[Sv...]]

Please sign in to view this quote.

But thats not the actual problem. It´s the constrain and the ass.criteria (or the math. targetfunct.) for the special geometry plane. What is OD or ID?

 

[[Ma...]]

Please sign in to view this quote.

OD - outter diameter - ID - inner diameter - aka OD = rod / ID = hole