# Making cuts on a surface

This is probably very basic but I fail to find a way to cut surfaces with an open polyline and pull a point of that polyline [and the surface the polyline encloses]

Example: a V shaped cut on a surface. How to achieve that? Further I want to ‘peel’ the V surface by pulling out the point at the base.
Like drawing fish scales on a surface and then pulling the tip outwards but still having a smooth transition at the base [see attachment - this was done by having a separate surface which is what I want to avoid]

I would really appreciate any hints, I find myself wanting to design this kind of surfaces rather often

Cheers!

Unfortunately, NURBS objects do not behave in this way. A NURBS surface is basically a set of interpolated curves in the “u” and “v” directions, which gives rise to a rectangular structure topologically. This rectangular structure can be twisted and bent, stretched and shrunk, but it remains continuous - you cannot put partial cuts in it and bend the “free” part outward as you would like to do (as you might with a sheet metal object). Any cut in the surface has to be either a fully closed loop if it’s an interior trim or cut all the way across the surface if it’s not. So you cannot do what you want as a single surface object.

One way to go about this would be to completely Split the surface with your cutting curve, shrink the inner surface with ShrinkTrimmedSrf, use Bend to bend the inner part, then Join to join the two into a polysurface. You may have to play with the bend a bit to preserve the impression that it’s a bent piece but not stretched. You could also simply trim out the hole as in the first step and then model your bent part separately with curves and then a surface.

Example file below…

–Mitch

SplitBend.3dm (290.9 KB)

Agh… alright, I’ll keep doing it manually
Thanks for the quick reply, Mitch!