If you instructed someone on how to use the machine after constructing their own parts, and they pressed the ‘on’ button, THEY built their own gun, not you.
There are machine shops in California that do exactly that right now. Nobody has busted them and cops are their biggest customers.
Yep, there is a M1911 manufacturer in Idaho that built 80% frames and invited all their buyers over to use their machines to finish the frame. Since they simply instructed the purchaser how to do it and did not do the work, there was nothing the feds could do.