Unroll srf wobbly errors

Wondering if anyone can shed some light on this one… Unrolling a surface (file attached) which has decent geometry is resulting in wobbly edges in the unrolled version in certain areas that don’t exist on the source surface. Rhino issue, my issue, not sure? Rebuilding the surface from scratch would be a pain with my workflow, but willing to do it if needed…

wobbly unroll.3dm (3.3 MB)

Move the object closer to the origin before unrolling.

I think there are a lot of self-intersecting curves, not unified curves and unwanted corners. By arranging a little I got this. Maybe it can help.

-Simonwobbly unroll_1.3dm (1.2 MB)

Hello - I do not have a good idea - most of the unroll looks OK but it gets squirrely at the one end… (I think I might untrim the surface, btw, and unroll the stair pattern as curves - the trims you have are a little odd in a couple of places where there seems to be zero width on the surface.)
I also got somewhat cleaner results by changing the degree of the surface to 1 in the linear direction and pulling the stair curves to the surface to unroll. It’s still messy near the end but maybe less so. Another idea which seems to work:
ExtendSrf > Smooth at a factor of about 200
Select the curves and the surface and UnrollSrf. This way the curves are farther from the ends and they seem to hold together better. Trim the unrolled surface back again with the appropriate curves.


hi all- thanks for the great input- david, interesting moving to the origin did something for you- no impact my end so that’s a bit odd.
Zsimon- you’re result looks pretty good to me, did you essentially just eliminate all the dodgy intersections to get your result?
Pascal- thanks as well- yours looks like a last case scenario, seems to improve things a little but not to the point of being able to trust if for fabrication.

All intersections and curves that actually did not touch each other were derived from a single base curve. Then a surface offset curve was created at the required distance. In this way everything is perfectly clean.