Problem with Sweep2

when something fails what i do is looking at the help page, in the lower part are they are commands listet that do similar actions.

Joseph’s use of a Tween curve triggered some old memories of my work in an aerospace Loft Lines dept. So I came up with this solution which is even simpler than the one I posted in the new thread. (22.6 KB)

And thanks to Baris for suggesting using the Help pages to learn about alternative methods. That is excellent advice.


Lifting and lofting the tween curve?

Sorry about that Joseph - it’s obviously something in the new version of GH.

Plus, upon close inspection I can see that the FitLoft does not actually adhere to its control curves:

Regular Loft works better but has nasty looking kinks at the corners:

Taking out the Seam adjustment fixes the Loft corners, but the resulting shape is looks like it has uneven thickness - even though the Loft matches the control curves.

This one divides a TweenCrv to try and smooth the bumpy transition points.

It’s not a great solution(not your fault). Tweens in general have issues with fillet curves (degree 2 curves with weighted control points). Zoom into the tween to see what I mean. The dividing smooths it but I think fitting both curves before the tween will let you not have to divide at all.

Interesting point Michael, but my Tween looks pretty good even at high zoom levels:

However, when I include the Loft surface I can see how it doesn’t fit the Control curves as well at it should:

Perhaps this is just a limitation of the software resulting from truncation/roundoff errors. I’ve dealt with that before and if that’s the case I know it’s not anything that I can do anything about. Practically speaking I think the errors in the Loft surface are so small compared to the size of the 3D printed filament I’d use to make the actual geometry that the mismatch would not be noticed.

But I’m glad I’m not building airplanes any longer.

From that image, you can’t tell where the surface really is. You are comparing a mesh derived from the surface with the input curves. Change the mesh settings and you will see something else.

OK, but what mesh settings do you mean? All the geometry is created in GH and none of it has been transformed to meshes. Plus the only mesh settings I know about are in Rhino, which I only use for exporting geometry baked from GH as an STL file.


What I am describing is not that. Degree 2 curves and fillets often do not tween nice because tween does not account for control point weights. Look at some other corners and the result tween control points (unless you are not using the same curve or have already fit / rebuilt it). It is not a display issue, it is an arc issue.

wim: Got it, thanks. I did not know “mesh” was the name used to refer to those parameters. I always set mine to High Quality, but never bothered to look at the actual values or try tweaking them. I am a bit surprised at how much detail there is there - and I’ll def. take some time to check them out. Some preliminary fussing suggests that the Loft surface really is OK in terms of meeting the control curves. So that is good news.

Michael - I see your point now, thanks. I understand the limitations of degree 2 curves (I call them conic curves), so I’ll see what I can do to make a better fit.

This one gets sloppy with the rail curves… (34.9 KB) (36.9 KB)

Very interesting Joseph - your longitudinal control curves work perfectly. I thought I’d see what happens if I switched to perpendicular curves, which was simple to do:

Comparing the 2 Loft results was fascinating.



In my current world of 3D printing this difference is not a big deal at all. But it would have been catastrophic in my former world of aerospace. Of course there is a major difference between generating screen displays and generating CNC milling machine toolpaths, so perhaps that could make up for the discrepancy between the two. I guess it comes down to picking the proper tool for the job at hand.