Union, Part become black.

eexpss · Post by **eexpss** » Sun Mar 12, 2017 1:45 pm

I want do this boolean operate:

shell - ( Array + Cylinder002 + Cone )

but when I select Array + Cylinder002 + Cone, make union, the result Fusion001 become black color. no error shown. Of course when make cut, also black. That result not my wish one.

Willem · Post by **Willem** » Sun Mar 12, 2017 2:01 pm

Hi, the problem is easy to solve, rotate the cylinder a bit and the fusion will succeed. This is a known bug in the OCC kernel

: Schermafdruk van 2017-03-12 14-55-56.png (233.48 KiB) Viewed 2408 times

triplus · Post by **triplus** » Sun Mar 12, 2017 2:06 pm

Nice one Willem.

P.S. Likely the seem edge was the cause?

eexpss · Post by **eexpss** » Sun Mar 12, 2017 3:01 pm

thanks Willem.

strange but interesting bug. lol

btw: Your Unity side bar is too strong.

Post by **Kunda1** » Sun Mar 12, 2017 4:45 pm

Willem wrote:This is a known bug in the OCC kernel

Which bug is this ? Can you reference it please? Thanks!

NormandC · Post by **NormandC** » Sun Mar 12, 2017 5:06 pm

I don't know if it's logged as a bug upstream. But seam lines of cylinders/spheres/tori are known to cause issues in Boolean operations when they align to each other (well-known cases are screw threads, there are at least a dozen of topics where Willem's trick fixed the issue). Surface tangency and coplanar faces are known issues as well.

It's mostly workarounds that we experienced users have found over time to bypass the kinks of the OCC kernel. Because of the way reports need to be made on the OCCT bug tracker, we have not reported it upstream (unless shoogen did at some point).

I know that we should document this on the wiki...

eexpss · Post by **eexpss** » Mon Mar 13, 2017 4:49 am

I agree NormandC, it a bug. OpenSCAD employs OpenCSG and OpenGL. and It never got error when doing Boolean operation, regardless of whether the target is aligned.

never as in this topic viewtopic.php?f=3&t=21215

Yes. Boolean operations are very sensitive to tangent and coplanar surfaces. A slight misalignment can make them fail.

NormandC · Post by **NormandC** » Mon Mar 13, 2017 4:54 am

Maybe not, but the OCC kernel is much more powerful than CGAL. OCC is a *real* CAD kernel.

eexpss · Post by **eexpss** » Mon Mar 13, 2017 5:15 am

Better efficiency, does not mean no bug.

Sure, openscad's render is too slow. In freecad seems no matter at rendering efficiency.

NormandC · Post by **NormandC** » Mon Mar 13, 2017 5:19 am

I was not referring to slowness (FreeCAD can be slow too!), but to actual functions. Try to make fillets or chamfers in OpenSCAD!

In any case it is more oriented toward programmers than CAD end users.

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