Rhino 6 - Surface weirdness

My first real work with Rhino 6 and I am encountering a number of unexpected problems. This surface reports as valid but does not render or take a displacement. The boundary frame is fine but the main surface is wonky in ways I don’t understand. The wireframe looks fine but it does not shade or render. I have include the Rhino file.

This is one of 12 regions created in the same way. 3 of those regions behave the same as this. The rest perform as expected. Any thoughts as to how I can make this work for displacement.

surfWeird.3dm (6.1 MB)

The ring surface is constructed badly. If you _DupBorder then _Dir on the resulting curves you can see that they have conflicting directions.


Take just the bottom curve, then _Explode it then select the left long curve from the kink, hide the rest. Then use _ShowEndsand zoom in on the one that is situated close to the surface kink



You can see that one control point lies beyond the end, you don’t want that.

If you delete that one control point, unhide the rest of the curve and join it back up you’ll find that you can trim your tubular shape so that you end up with a proper trimmed surface.

I ran _UntrimAll on your surface, after hiding all other objects, to get the tubular surface back, then used the cleaned up curve to trim it.


You’d probably want to clean up both edges of the ring surface, though, since there are some overlapping curves and such. Before joining them together probably a good idea to ensure they all are oriented in the same direction along their ring.

surfWeird_NL_potentialfix.3dm (6.2 MB)

Thanks Nathan. That pointed me in the right direction. All fixed now.

I am surprised at these issues tho. All my source curves were created in 2D the same way. degree 1 closed polycurves - FilletCorners - FlowAlongSrf - then Split and OffsetSrf. 59 total closed curves and apparently only 3 were wonky. I guess I should be happy it was just 3. I do have a concern moving forward as I need to close this model up for 3d printing.
Many thanks again.