offsetSrf creates 2 extra surfaces not required

I know I can model this simple offsetSrf in many ways - however can someone explain why offsetSrf creates these 2 extra surfaces (blue layer) ?


offsetSrf.3dm (87.4 KB)

Not sure what you mean? If you click on the main surface and offset it seems fine?

offsetSrf.3dm (255.6 KB)

These extra surfaces appear with offsetSrf solid=yes


Hi Keith - try:

MakePeriodic the surface.
Trim with the border curves

I’ll check into this - there is no naked edge there but the circular edge there is very very slightly out of tangent where it meets itself - my guess of the moment is that this causes the offset not to meet itself perfectly and so the surfaces are added, MakePeriodic makes that surface smooth where it ‘meets’ itself there at the seam.


Thanks Pascal, RailRevolve also creates a better surface - which is periodic.