Rebuilding circle with little deviation ends up w. .5mm diff. in diameter

Hello everyone,

i have the problem that I would like to blend two surfaces. One of them is a circle (100mm diameter).
When I BlendSrf them, the circle is automaticly rebuild and the diameter is off by sometimes 0.5mm.
I thougt I could work-around this problem, if I rebuild the circle before I BlendSrf them.

I tried rebuilding a 100mm diameter circle with 16 points and degree 3, resulting in 0.00320616 maximum deviation. But still: when i check the diameter with the diameter command at some areas the circle has a diameter of 100.503mm … how can I minimize this number?

Another example: 50mm circle > rebuild with 18points + deg. 3 (0.000996221 max deviation) > some areas have a diameter of 50.262mm or 49.722mm…

Thanks a lot.

Hi Niklas - please post the objects in a Rhino file.

Rebuilding circles is pretty good with degree 5 and 24 points. But it will always be an approximation.


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Circle Rebuild.3dm (59.1 KB)

Thank you! The degree 5 and 24 points tip worked fine :smiley:

Hi Niklas - I am not clear on the original problem - what surfaces are you blending and what rebuilding takes place in that process?


Here, take a look. I still have a 49.834mm diameter at the end on the Quad point after the BlendSrf
BlendSrf Problem with diameter.3dm (1.9 MB)

Hi Niklas the radius will vary more, locally, than the deviation from the true circle due to slight variations in curvature along the edge. The deviation from the true circle is ~.0001 or less and the overall size of the edge curve is
50.00000 by 50.00000 millimeters


How did you get the numbers? I would like to analyze this by myself in the future. Thanks!

Hi Niklas - CrvDeviation and BoundingBox commands.


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Thank you! Really helped :smiley: