Extrude cut fail. Bug?

Hi everyone, I am not able to make a extrude cut like the object in the lower right corner. As long as the object on the left has a square inner cut, I can only make a triangular cut on either side but not both. Any idea why?

Thank you in advance!

I think the reason is that the extrusion algorithm “thinks” that the double extrusion would create a non manifold geometry.

The 2 cubes in fig e) are non-manifold object, so it has to be 2 separates objects.

If you look at the short video below, you will notice that the extrusion behavior is very different when you extrude one triangle or both triangles:

  • in the fist case, extrusion occurs immediately as the result is always a manifold geometry
  • in the second case, extrusion starts by creating 2 bodies until it could totally cut the initial body and create 2 bodies, so it is still manifold geometries all the time.

When you extrude the close wall shape, I think the tools would like to create 2 separate bodies but cannot because the initial shape is a close wall shape.

The final shape be can built successfully with the union of 3 shapes, but I’m not 100% certain that the resulting shape is really manifold.

So it is clearly a border case, which is not trivial for the algorithm to handle.



Thank you very much for the prompt response!! I really appreciate it!
Do you think that this should be considered a bug that needs to be fixed? I think it is pretty trivial but apparently it is not trivial at all to the application.

While the workaround that you have provided solves the problem, I actually need to have the same kind of extrude cut on all sides of the closed wall structure so workflow wise it would be to troublesome.

I hope that Shapr 3D could release an update that fixes this problem.

Thank you so so much again for helping me out! I really appreciate it!!

you sir have a good day!


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Hey! Unfortunately, the modeling kernel (Parasolid) does not support non-manifold bodies. We might implement an automatic workaround option, but not in the near future.


Second thought, I wonder if the bug is not to be able to union the 3 parts, as the resulting body is actually not manifold.
If you try to extrude from the sketch below, it fails with an explicit message : non-manifold body.

Be aware that creating the body with the union of 3 bodies just “fools” the algorithm, but in fact, the resulting body can’t be manufactured.
So if it has to be airtight, add a small wall to make the connexion, or if not, add a small gap (even 0.01mm width is fine and won’t be noticeable). Doing so, you will create valid geometry and will save troubles later on.

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I have to correct myself:

Well, the answer is no, this is not a bug as it is extremely well implemented actually and union of the shapes does not fool the algorithm at all.
If you zoom to the suspicious edge, you have the answer : Shapr3D automatically implement a small arc of circle and generates actually 4 separated edges and a small portion of material actually joining the left and right part of the body.

… well, this is so true I didn’t notice it myself :rofl: but Shaprd3D does it automatically for us :+1:.