Trouble with loft and offset surface commands

sam_tocci

I'm new to OnShape and I'm having trouble with the offset surface and thicken commands on my curved surface (link to the project below). What I thought would be a simple loft has stumped me.

I'm trying to replicate a pinched rectangular extrusion, like if you squeezed the edges of a foam card.
I started with three planar curves and lofted them into one surface. Right away I notice a seam in my surface that stems from where my tangent curves meet in sketch 2 (and sketch 4, being identical).
Creating composite curves and lofting didn't seem to have an effect. 

This causes problems when using the thicken command, or offsetting the surface, the resulting edge has a sharp change in direction at this seam. I would like the "thickened" object to have a smooth continuous edge that is normal to the original surface at all points as though it were once flat and then pinched into this shape.




I also tried to manually draw the lower edge using a bridging curve, but I couldn't find a way to constrain it to be equidistant from the original edge. At this point I realized I was overcomplicating things and decided to ask the forum.
I appreciate any and all help, thanks in advance!

https://cad.onshape.com/documents/d9f0764c4ad0eba7932c7b0f/w/392f5da0b9e6fc1c77c82e60/e/326b09df5d9b0af17129bb0e

John_P_Desilets

@sam_tocci Thank your detailed post. First off, you don't need to create a composite curve for each sketch before creating the loft feature. You can select the sketches from the feature list and the loft will work. 





In the loft feature, the start and end profile conditions needs to be set to "Normal to profile"



Now when you thicken the surface, the thickened part will not buckle. This is because the surface is properly constrained. 



Here is the link to the document. Let us know how you make out!

https://cad.onshape.com/documents/6f896a137914caaab88ff2bb/w/68899dc66e468bd00db32f99/e/55c049044033281e988c05ba