Sweep1 twisting in 7WIP

Hello all,

I am getting different results when I run Sweep 1 in Rhino 7.0.19274.12465. The surface seams twist when they should not. I’ve copied the same curves into Rhino 6 sr18 and they behave normally.


Rhino 7, exact same curves

Is anyone else having trouble with Sweep 1? Here is the file. Sweep 1.3dm (219.2 KB)


Thanks for the report. It looks like a bug to me.


Thanks Lowell! Any changes to the Sweep command have a HUGE impact on my workflow.

If I can make a request in addition to the bug fix, can the “Refit Rail” option be made sticky? Right now if you check refit rail, Rhino will remember until you close rhino. When you open a new Rhino, it goes back to the default value of Refit Rail = No.

In fact, if Refit Rail = yes could be the default that would be even better. If I’m not mistaken, it used to be that was in Rhino 5. Simple Sweeps were the exception in Rhino 5 and you had to opt in to get them. Now in Rhino 6 & 7, Simple Sweeps are the default (when possible) and we have to check Refit Rail every time to avoid them.

IMHO Simple Sweeps are never preferable to the old “regular” sweeps from Rhino 5. The surfaces may have a low control point count, but they are not as predictable or accurate in form as the “regular” sweeps were.

I guess this would apply to both Sweep1 and Sweep2. At least in Sweep 2 the refit rail option turns on automatically when you use Maintain Height.


@pascal - Do you have an opinion about the RefitRail stuff there?

Hi Lowell - my general preference is for simple - I guess I need to know more about why and where that is not a good thing.



Hi @Pascal,

Thanks for chiming in. Here’s an example of how Sweep1 changed from Rhino 5 to 6.
Rhino 5

Rhino 6 without Refit Rail.

In my opinion, the surface given by simple sweep in the second example does not follow the curve of the rail nearly as well as the first example.

In Rhino 6 you have to opt in to Refit Rail (every day) to get a sweep that looks like the one from Rhino 5, and Rhino 4 and 3. It was a big surprise when this changed in 6. I’ve been using Rhino for a while but didn’t even know they existed until I started getting them unintentionally when I switched to Rhino 6.

Sweep1 & 2 are everyday tools for me, especially to build rings. I find now that my models often meet the criteria to end up with a simple sweep. Maybe I’m missing something, but I have yet to find a practical purpose for the simple sweep. (at least in jewelry design. I’m sure there are applications elsewhere)

I’ll see if I can dig up another example too.


  • Mike
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Hi Mike - thanks, no need for other examples, I understand what you’re getting at.
I wonder if the ‘Simple sweep’ as an option needs to make a comeback. That is maybe more straightforward. One thing to note is that we took quite a lot of flack over the years for how ‘unnecessarily’ complex Rhino sweeps are when the input is simple.

Actually, @MikeM - making the setting persistent between sessions would also do for you, correct? I guess I prefer that, assuming it is possible, which I think it is, since it is less disruptive to the existing UI.




Hi Pascal,

I know many of my colleagues here would be a fan of of turning Simple Sweep back into an option that you have to opt in for.

I didn’t know about the flack that you got about it earlier. I wasn’t as active on the form then. I’m not surprised though. I figured McNeel wouldn’t change such an important tool on a whim.

Maybe a compromise would be to let either the “Simple Sweep” option or the “Refit Rail” option persist when you close and open Rhino. That way we could just check it once and forget about it. The people that like their simple sweeps can get them and those of us who don’t can get the “complex” sweeps.

hm - I see that the dash version seems to have been left behind - at least the options and how they work are unclear to me at the moment.



I think that would be a decent compromise. If other people requested the simple sweeps, I’m sure they have good reasons. Simple Sweeps just seem to get in the way for our workflow.

We teach new jewelry designers all the time and explaining the difference between simple and complex sweeps to new Rhino users is “complicated.” (Pun intended) Also getting them to consistently check the Refit Rail box is always a challenge.

Don’t get me wrong, I (and my fellow instructor/designers here) would prefer to see “complex” sweeps become the default again. But if that’s not feasible, then yes making the setting persistent between sessions would do.

RH-55364 and RH-55398 are fixed in the latest WIP

@brian @lowell
Hello all,

I just checked this again, and the Refit Rail’s option in Sweep 1 is not sticky from one session of Rhino to the next. I thought this was fixed. I am running the (7.0.20014.11185, 1/14/2020) WIP.

Also, can we add this to Sweep2 as well? For the exact same reasons as making Refit Rail sticky for Sweep1.

RH-55398 is fixed in the latest WIP

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Thanks all! That works for Sweep 1! :+1: :grin:

Can we add the same feature to Sweep 2?

Sweep2 request added as https://mcneel.myjetbrains.com/youtrack/issue/RH-56768

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