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Flatness control in a given zone of the model


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Hello and I wish you all the best in the New Year.

I have a situation where I need to check the flatness in a zone between two circles with a diameter of 20 and 22 mm.
I admit that I did not find anything on the forum or in the program help on this subject.
If there is such a possibility, or if someone has worked on a similar topic, I am asking you to guide me.
I'm add a simple draw and hope it's clear now. 
Only red area need to be checked. 




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technical is this simple the question how to achieve a good selection on actual to use it to create a fitting plane. Afterwards you can use this fitting plane to create a flatness tolerance.

For instance you can use Select by Geometric contour to achieve these goal. As precondition please ensure that the triangulation for both actual and nominal at the area is sufficient (i.e. your edge length should be not too big, so that multiple triangles can be selected).

  1. Create an nominal circle at required position with diameter 21 mm
  2. Apply measuring principle None
  3. Create an selection using select by geometric contour (distance is now 1 mm) on the CAD
  4. Create a fitting plane
  5. If you have achieve a very good selection on the nominal you could try to create the actual plane using the measuring principle "Fitting element". Otherwise it may be a good idea to modify step 2 and link to a actual circle instead. Afterwards you can use the measuring principle "Referenced construction". 

Hope this helps.

Christoph Schult

PS: The simplest solution would be of course to have a single patch in your CAD file that describes the needed area. Then you can simple select this patch to create the nominal fitting plane. Of course this is often not possible then try the geometric contour approach mentioned above.

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  • 1 year later...


Just tried the above steps and struggle during step 5 with the second option (Otherwise ...).

From step 1 I have a Circle 1 as Nominal Element. Then I tried to define the measuring principle "Link to Actual Element..." which allows me only to choose other elements, but not the circle from step 1.

Not sure what I missed here.

Thanks for some more details.

Martin Ziegler

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  • 1 month later...

Hi Martin,

Maybe this will help.

After step 2 create a Cylinder/Cone base section based on the circle give no measuring principle.



Now you have to Go to Edit -> Selection in 3D -> Other Selection -> Select by Curve.



Now Construct a Fitting Plane with Measuring Principle - Fitting Element and Tolerate the flatness





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Are you using a CAD model with the scan/mesh? If so you can cut a face in the CAD model. Every software has a feature to do this. Solidworks you use the splitline feature seen below...this lets you select specific areas to measure. I used this frequently.




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