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!

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!

Hi,

I think the reason is that the extrusion algorithm â€śthinksâ€ť 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 Iâ€™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.

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Hi,

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!

Best.

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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.

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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 â€śfoolsâ€ť the algorithm, but in fact, the resulting body canâ€™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 wonâ€™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.

â€¦ well, this is so true I didnâ€™t notice it myself but Shaprd3D does it automatically for us .