Hi Nick, unfortunately the surface thickening mechanism in the geometry library that MoI uses is pretty limited - it can only really thicken a single surface or one that has right angles in it, not one that has has surfaces meeting at all different angles like you've got there. Those cases add a lot of complexity because pieces that meet all at different angles will make a type of "branching vertex" result. The library does not deal with that case at all unfortunately, it assumes that each vertex in the original shape matches to just one vertex in the offset one. The thickening can work better if you are starting with a solid rather than an open surface, that's a pretty different process.

- Michael