When I do OffsetSrf on this surface it creates weird artefacts.
180126 Offsetsrf.3dm (667.7 KB)
Hm - yeah… I’d make a PlanarSrf from the outline shape - is there a reason you need the surface to be made the way it is? A trimmed plane is a much better candidate. In your surface there are places where the U and V are parallel - that is not a good thing when it comes to offsetting.
-Pascal
The fixing is not a problem… I just thought you guys might find it useful if I report this unexpected result. Even if that original surface was not created in a good way, it shouldn’t be offsetting the surface double the amount in some spots, right?