Hi, would like to shell this twisted model and then connect it with other pieces.



As you can see, there is a lot of twisting in the edges because of the bent shapes.


If you shell a quarter of a sphere you get sharp edges. This is what I'd like to achieve.


One idea was to join 4 pieces of my model, shell it and then use Boolean|Diff to cut it into 4 again. But because of the way it looks this is not possible to shell.



Anyone have any idea? Maybe I should try to enlarge my model a bit all around, shell it, and then cut of the "waist".

/Lars

Hi Lars - in this case it looks like there is a kind of messed up edge in this area:



The trim or boolean did not do a great job of calculating that bottom edge there.

To clean this up, I used the ShrinkTrimmedSrf command (it is a special command you can run by a keyboard shortcut) and then selected the trim curves and used delete to "untrim" the surface and that gets a nice trim boundary on it.

That version is attached here as shell2_fixedcorner.zip


With that tuned version, shell or offset should now work on this case, previously it would shoot a strange little bit off to the side right in that area where that wiggly edge was at.


But it sounds like you may not want a "true" shell in this case? The offset and shell command will create an outside surface that is a constant distance away from the original. So if the surface is twisting, the offset will also twist as it must in order to keep a constant distance.

If I understand you correctly, it seems like you may want a shape that does not have a constant thickness to it? To do that you will need to construct the surface manually using something like sweeping, I'll see if I can give you an example.

- Michael

Hi Lars, if you want to emphasize a clean edge on this model, you can draw in a couple of lines here:



Then for each one of those you can select the line, then run Construct / Sweep and select the edge as the sweep rail. That will create this kind of a thing:



Is that the kind of thing you are looking for?

To finish this up you will need to manually create the outside surface - it won't be a surface that is a constant distance away from the existing one so you wouldn't be able to use the Offset or Shell commands to create it, you will probably need to put in a bunch of sections and use the Network command to build it.

But I'm not sure if I understood what you are trying to do.

- Michael

Hi Michael, and thanks. I needed perpendicular edges (at least I think thats the right terms in english). Like this:



Actually half the model looks like the one below, but I couldn't shell it, so I tried dividing in three parts, which then would have to have perpendicular edges so I could join them together again. But as I said, thats only half of the model, the whole model is the one I recently posted a photo of in plywood.



It's bedtime here in Sweden, but I will have a closer look at your examples tomorrow. Thanks again.

/Lars

Hi Lars - well definitely an offset of your existing surface will not produce those kinds of edges, due to the shape of your surface.

Offsets of a surface happen along the surface-normal direction.

If you look at the Front-side view of your object, this is what it looks like:



I've drawn a couple of lines in there to indicate the surface normal direction along the silhouette.

With the surface normal pointing off to the side like that, the offset surface will be created along it and will be off to the side as well. That's basically the definition of what an offset surface is.

For a sphere, the normals are pointing upwards, like this:



That's why the sphere creates vertical edge pieces, because the sphere's surface normals are pointing vertically there.


So anyway, that's why Offset/Shell will not create what you are looking for in this case.

Other than creating a custom surface using something like Network, I guess you could try to create an extended version of your surface and then offset that and try trimming all that back to an edge...

I'll try to take a look at your shape and see if I can suggest any other way.

- Michael

Hi Lars,

If you could post or e-mail me the more complete piece you showed above:



That might help me give some better suggestions.

It's otherwise kind of hard for me to visualize how the pieces are supposed to fit together.

- Michael

Hi Michael, now you've provided me with a lot of knowledge and I thank you very much! I sat down to make an image so I could show you what it is I'm trying to do, and now I feel like a complete idiot...

Last night I tried this but it took forever and ever and still no shell. Must say that MoI performs excellent in these cases, it doesn't hang or freeze, it just calculates and if you wish to abort you just click cancel. This is great.
I believe it was rather my laptop that was tired last night. But now it works. This is what I've tried to do all the time.

I cannot join the two halves, left and right, but MoI could still create a centerline shell. The maximum shell thickness is 0,25

Will try the Network command, that together with the sweep tecnique you showed me would possibly give me more control over the way the edges look.

/Lars

Hi Lars, I just sent you a PM as well - I think the "secret step" in this case will be to not use Shell to create your final surface.

Instead use Offset, but don't attempt to offset the surface - it will not create the kind of edges you want since it will follow the surface normal as I wrote previously.

Instead offset each of the curves that you used to Loft your surface in the first place. Then loft a new one through all of those new offset curves.

This does not create an offset surface - and actually the outside and inside surface will touch each other along the vertical axis line.

But it seems to be pretty close to what you are after:



This seems like a better strategy to pursue.

- Michael

Hi Michael, thank you for sharing the secret.. This gives me the kind of edges I was looking for.

/Lars

Added to the Sepecial Thread Gallery (before a cool rendering :)

Have you a 3dm of that?

Hello Frenchy, it's meant to be "rendered" in real life like a sculpture. But if you can do a cool rendering I'd be happy to send you the 3dm.

/Lars

@renklint
A cool rendering I don't know but surely funny image!!
Don't sent now!
I will recall you in 10 days !

Hi Lars, it is looking great! I hope you will be able to post a photo when it is built.

- Michael