Thickening a Complex Polysurface

I have a complex polysurface that I’m trying to turn into a 3mm thick closed polysurface, by thickening outward (opposite direction of the surface normals here).

Q: How do I make this into a closed surface with a minimum thickness of 3mm, while allowing a tolerance for it to be thicker in places if needed?

OffsetSrf results in a messy, open geometry any which way I’ve tried, and necessitates a very manual and tedious rebuild of the offset surface.

Thanks for any advice!

helmet_innersrf.3dm (1.5 MB)

You need to plan out how you’re going to do this from the start for OffsetSrf to work without cleanup(or with minimal cleanup.) But if you actually want a variable thickness…well you’re into a lot of manual rebuilding anyway.

The result of OffsetSrf I got wasn’t, by the standards of offsetsrf, that bad, the problems were mostly in areas I would totally expect them to be. Your inner shell needs to be very well modeled with tight precision for the offset to be clean, and there are a few areas that are kind of wonky, like for example the upper rear area, that’s just a mess and should maybe be treated as a totally separate feature from the rest of the model.

I was going to respond more or less as Jim did - but just as a further, possibly helpful, step, if you extract the fiddly detailed bits like the more complex vents and offset them Solid=Yes separately from the main ‘smooth’ bit, then you will have some work to do but it may be clearer - the edge surfaces will need to be extracted and deleted but the result may be more tractable for the ‘by hand’ work.