Creating Closed Polysrf Helices

Rhino
1

Helices Diagnosis.3dm (5.0 MB)

Hi,

I am trying to create a series of helical forms by sweeping a cross section around a helix.

The attached file has a set of 4 forms with the sweep shapes, primary axis, helix, polysrf etc. each on colored layers. I am trying to split these forms into lengths that are an equal number increment of the helix pitch, so they can be stacked and combined. I’ve tried trimming them, splitting them, boolean splitting them, boolean difference, etc, and I always end up with open polysurfaces. I’ve tried cap to close them. I’ve also tried duplicating the open edge, planar srf, and then join, but that doesn’t work either.

Can someone help me figure out how to work with these in a way where they are closed polysurfaces, so I can boolean union them to other objects?

Please take a look at the attached file if you can, and play around with it a little bit.

Thank you very much

2

Here they Split and then Join without naked edges just fine, or am I missing something?

Skärmbild 2025-11-13 22.13.14
Skärmbild 2025-11-13 22.13.141660×544 629 KB

Split Join.3dm (9.5 MB)

3

Hi,

Thanks for chiming in. I opened your file and tried again and got 2 of the 4 to split and join into closed polysurfaces, but 2 are still not working.

I made an effort to construct all the geometry very cleanly, and I would like to work with this type of geometry on a CNC lathe, so I’d like to figure out any applicable tricks. Something about running Sweep 1 on a helix creates some weird geometry.

Thanks again. Any other ideas would be very helpful.

4

In general you won’t get a properly joined polysurface with the method you are using.
The sweep1 command is just not that smart. You are ending with naked edges that run the length of the helical form that you don’t want. The fix is fairly simple.

When your sweep shapes are composite curves (curves composed of sub-curves) all you have to is explode the sweep1 result and then join. Three of your examples can be fixed like this.

When your sweep shape is a single curve the sweep result is a single surface. A single surface can’t be joined to itself so you end up with a naked edge that runs the length of the helical form. To fix the one example that is a single surface you can use split by isocurve and split the surface at the rail curve. That makes it two surfaces that Rhino can join

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image374×231 24.6 KB

5

Wow, thank you so much. That is a very easy fix. Just the information I was looking for.

Do you have any other suggestions for ways to create this type of geometry.

Thanks

6

Nothing comes to mind.
Other than that problem with naked edges created by sweep1 you seem to be doing quite well.

There have been numerous threads on this forum about creating machine screw threads that might be of interest to you.

7

Thanks ! I’ll take a look.