Releasing Surface Tension?

I am using Patch to create surfaces from curves. Often it works perfectly! BUT sometimes it seems to fight back. I have to add a bunch of cross sections to create the surface but it still does not want to be a smooth surface. See attached images. It seems like there is a preprogrammed tension in the surface caused by the main outer curve for some reason??? Is there tension loaded into the curves that can be altered?

I don’t think the Patch is the answer, you can try with all other commands and trim the boundaries later.

How would you create a surface from these curves??

Hi Tom - please post a file with those curves.


TestCurves.3dm (3.2 MB)

I was able to et the surface smoother by reducing the stiffness down to .1. I hadn’t messed with stiffness before.

Hi Tom - ideally, is this curve, in top, visually a single curve


and not slightly crossing itself, like here:



Sometimes I start with them in alignment and then twist it accordingly. It certainly makes a difference moving the points around but sometimes it makes no diff… in this latest case it was making no difference. You can see the surface pulled out to the right, is a better surface generated just by reducing the stiffness to .1

I am trying to learn if there is another way or a tool for getting the surface to react better to the curves provided. As you can see in the initial image I posted, there is a bad waviness to the surface. Perhaps reducing the stiffness is the best I can do?

Hi Tom - I am trying to get enough information to suggest a different surfacing tool. Sweep2 might be a way to go,

TestCurves._PG3dm.3dm (89.6 KB)

but it would be better to eliminate the details - the sharp turns - in the rails and trim those in afterwards.


Did you break up the single long curve to enable the use of Sweep2?
I use sweep2 in some cases and it’s great, in these surfaces, the main curve really needs to stay single and continuous because patching the end closed after is problematic. I included a completed arm in that file so you can see where I am going.
This gets confusing, haha. Thanks for helping.

I like to get specific and have sharper corners in certain areas, see attached image…

Yep, and that is one advantage of using Patch - you get to trim the shape to taste. I’d try using fewer little shape curves and see how that goes - but I’d be inclined to work out a way to define a slightly over sized ‘main’ shape that is more closely controlled, and then trim out your final shape - it could even be re-used.


I think I tried that idea in the past but I had to project the curve onto the surface to trim and whenever you project a curve it destroys it with millions of points and things get messy fast. I end up with good curves, trim curves…