Ruled surface between curves with a negative offset

I’m trying to build a series of surfaces which are extruded to build a tiered lamp. I build a set of curves, and then use ruled surface with a list shift and shortest list to build a set of surfaces between each pair of curves. However, I need the inner curve to overlap the previous surface by a small amount, so use a negative curve offset, and this causes problems when creating the surface with ruled surface with more complex curves.

I think the problem is similar to this question, but unfortunately I don’t think I can apply the same work around?

Is there a way to reconstruct the curves in such a way that I can reliably create a ruled surface between them? I’ve uploaded a simplified definition with internalised data that hopefully shows the problem I have. Thanks!

Lamp 002 - (24.5 KB)

I think it would make sense to add pufferfish as a tag so other people know they need this plugin to help you. I’m not using it so for me it was a waste of time to download your file.

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P.S. Instead of extruding them all to different heights, maybe I should have extruded them all to the same thickness and then moved them in Z?

Lamp (15.9 KB)

V2: one stepped “Closed Brep”

Lamp (16.7 KB)


Sorry @martinsiegrist, I thought I’d deleted those components in the simplified file that shows the problem I’m having — it shouldn’t be dependent on Pufferfish :thinking:

I’ve attached a version which definitely doesn’t use Pufferfish!
Lamp 002 - (13.3 KB)

Thank you so much for taking a look.

The overlap is needed so I can assemble the final prototype — I’m currently 3d printing the layers separately to avoid supports, so an overlap is needed to bond them together. I’ll likely be slip casting so there needs to be some thickness through the step boundaries. And yes, in my final assembly I’m extruding each surface by a fixed amount to create a closed brep for each layer and moving in Z.

The example you gave overlaps the steps vertically, but I’m trying to move the inner curve on each step inwards which is where I’m having trouble with Ruled Surface? Would boundary surface work better as in your example?

What’s wrong with a vertical overlap for bonding layers together?

I have no idea what “slip casting” means?

They might work fine, I don’t know unless I try it. Doing that now but it’s a little hard to be sure.

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@Joseph_Oster using Boundary instead of RuleSrf as in your example works perfectly, thanks!

And it works great with a negative curve offset, so it’s all fixed!

Screenshot 2024-01-26 at 17.47.37

OK. I added the purple group to offset the inner curve and it seems to work.

Lamp (28.7 KB)

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Amazing, thank you so much!