Yep. Clean room reverse engineering also steers clear of copyright, and hardware design cases are very difficult to prove unless it's a direct knockoff -- if co

Yep. Clean room reverse engineering also steers clear of copyright, and hardware design cases are very difficult to prove unless it's a direct knockoff -- if copyright worked that way, then things like 3rd party auto parts manufacturing couldn't exist either. 3d sintering is different because as you said, sintering is patented. Physical products have a bunch of rules that are significantly different from software products, and the area is really murky. I don't know of any GPL hardware cases, but would doubt they'd get very far unless you were able to show direct infringement, which is a lot harder.