Datum system shifted/tilted

[[Ph...]]

We are currently creating a new template for ISO GPS-related dimensions.

Design intends:

Datum A is the mid plane of the 2 drafted planes A1 and A2

Datum B is the mid plane of the 2 drafted planes B1 and B2

Datum C is a plane normal to the axiy.

we have noticed that the actual fitted plane and the displayed coordinate are not perfectly aligned. There appears to be a slight angular difference as well as a small positional offset between them. computation mode ISO 1101 or geometry shown similar deviation but exactly the same.

Any idea how to fix it?

[[Ma...]]

Do you really need datums in this order?

I would start with C ( which is not shown ) and then A and B.

I think problem can be that planes used in A and B are angled and Inspect can interpret model edges wrongly ( you see nice faces, but Inspect is secretly transforming this model into triangle mesh )

I would use a plane from 4 corners close to A1B1, ... and make section on those A1,2 and B1,2 - then use symmetry from those lines.
You get from B only direction - it's not compensating tilt, and according to ISO/ASME it will be evaluated as perpendicular to A.
Also i think A,B planes are short in height.

Edited 6 hours ago

[[Ph...]]

this part is 130mm long, the cross section is 30x20, therefore C cannot be the primary datum

according to ISO I can define a datum between 2 drafted surfaces, it is a wedge.

is there any way to refine this triangle mesh?

[[Na...]]

Hi Philippe,

if a symmetry plane is defined as a datum, it is created like this (ZEISS Quality Tech Guide) : 

Middle plane of an inner element

Middle plane of a maximum inscribed plane pair

The inner planes get inscribed iterative according to the ISO standard. This computation method is not possible to recreate using standard elements. When the standard in the datum system is set to 'geometry', the datum plane and the symmetry plane should be at the same position. You could verify by checking the symmetry plane for position using the datum system with the positional check also set to 'geometry'. 

Nanno

[[na...]]

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Isn't function Use nominal angle supposed to automagically solve this case?

 

 

 

 

 

Edited 2 hours ago

[[Na...]]

The image below would be a wedge probably, "use nominal angle" covers the case of datum elements with an angle between them:
ZEISS Quality Tech Guide