Offset srf does not run properly on this surface (I see there is an abnormality in normal directions).
Offset srf incorrect.3dm (126.5 KB)
You are careless.
Offset srf incorrect-1.3dm (210.9 KB)
This surface is not offset correctly. I thought it worked with Rhino 7, but nothing.
problem offset srf.3dm (195.6 KB)
Pascal Golay wrote: Surfaces that have segments that are tangent and not curvature continuous (e.g. often created when the input is tangent arcs and straights) can cause problems for the meshing needed to display the object in shaded modes… Run the DivideAlongCreases command, with no pre-selection and set SplitAttangents =Yes, then select the object… By splitting the surfaces up at tangent locations, each new face is meshed independently. This is generally a better situation for other operations as well… Splitting should just happen, and merging should be the thing you have to do deliberately. I have not got any traction with that over the years. SplitAttangents=Yes/No in some commands is the best we have. source: Cap command is corrupting the surface
divide along creases also helps before exporting as STL for 3d printing.