Subtractive pipe issue

[willemx]

I am trying to create a fillet on the edge of a simple part using a subtractive pipe, but after creating the pipe, the part turns black.
Can someone show me what I am doing wrong? I have attached the design.

system details:
OS: macOS 10.16
Word size of FreeCAD: 64-bit
Version: 0.20.2.29603 (Git)
Build type: Release
Branch: (HEAD detached at 0.20.2)
Hash: 930dd9a76203a3260b1e6256c70c1c3cad8c5cb8
Python 3.10.8, Qt 5.15.4, Coin 4.0.0, Vtk 9.1.0, OCC 7.6.3
Locale: C/Default (C)

[Shalmeneser]

PartDesign_Fillet is an easier tool !

Your PartDesign_SubtractivePipe cuts itself. Modifying the radius there cure the problem.
You should use Sketcher_ConstrainTangent exclusively to get a smooth line.
It's better to attach the pipe form to the pipe path.

btw, it's better to keep the '[ code]' tag around your infos.

[papyblaise]

are you happy whuth that

[willemx]

@Shalmeneser :
Thank you for helping me!

PartDesign_Fillet is an easier tool !

Yes, but it's nearly impossible to use in a complex design that changes a lot. The infamous topological naming issue causes fillets to break after nearly every change higher up in the design tree.

Your PartDesign_SubtractivePipe cuts itself.

Yes, but why should that be a problem? That could mean that things get subtracted more than once, but that should result in the same shape. does this mean that I cannot subtract from concave shapes, but only from convex shapes?

Modifying the radius there cure the problem.

You created a new design (subpipe_SHALM.FCStd) with a smaller radius and a different position for the profile. Does this design render ok on your system? On my system it still produces a black part:

Screenshot 2023-01-28 at 19.51.37.png (64.3 KiB) Viewed 592 times

Even if I make the radius much smaller, the part remains black.

It's better to attach the pipe form to the pipe path.

I thought I did connect the profile to the path (see screenshot in my first post), or maybe I don't understand what you mean by this?


@papyblaise
How did you create this design?

[papyblaise]

I made the sketch of the keyhole without the small interior radius >Pad then I used the Fillet function on the lathe, and again fillet on the 2 small angles

[chrisb]

Your PartDesign_SubtractivePipe cuts itself.

Yes, but why should that be a problem?

Maybe it should not be a problem, but actually it is what it is. This restriction comes from the third party geometric kernel, and from what I heard from professional systems, they have similar restrictions.
I can't give the implementation details, but I can understand why it is treated this way: In my naive imagination a sweep works by moving the section along the path, but I don't think there is actually such a time component. And with self intersections there are places in 3D space which are at the same time inside and outside of the sweep. It's somehow similar to having sketches with T-Joins, which cannot reliably be padded.
In a different world there may be a different interpretation, but currently we have only this world to play FreeCAD in.

[willemx]

@chrisb
Thanks for the explanation; I was already afraid it would be something like this.
(makes me wonder though how the fillet tool is working internally...?)
So I must resort back to the fillet tool and pray that the TN-problem will be fixed real soon now.

@papyblaise
Yes, with the fillet tool it's no problem at all.
...unless you need to change something: I just added a little hole to the pad and your nice little fillet is gone:

Screenshot 2023-01-29 at 08.17.55.png (111.63 KiB) Viewed 424 times

[chrisb]

(makes me wonder though how the fillet tool is working internally...?)

It would work here, if you make separate sweeps, and I can imagine that fillets do something similar. We know from a fellow forum member, that the fillet code in OCC is extremely tricky, so that - at that time - nobody in the company dared to touch it.