You would think that the country that came up with the STEN gun would not be so foolish as to think that gun control is just a matter of watching the borders. Any cellar or garden workshed could be an arms factory.
The dangerous thing about volume printers is not that they could be used to make weapons, but that you can't tell the difference between a machine used to make chesspieces and one used to make guns. Every owner could have a legitimate and innocuous reason to have it, and therefore you have no probable cause for additional scrutiny on anyone.
With a CNC mill/lathe, if you don't actually need one to produce something like custom auto or motorcycle parts, using it to produce solid aluminum garden gnomes might be seen as suspicious rather than a plausible cover.
The dangerous thing about volume printers is not that they could be used to make weapons, but that you can't tell the difference between a machine used to make chesspieces and one used to make guns. Every owner could have a legitimate and innocuous reason to have it, and therefore you have no probable cause for additional scrutiny on anyone.
With a CNC mill/lathe, if you don't actually need one to produce something like custom auto or motorcycle parts, using it to produce solid aluminum garden gnomes might be seen as suspicious rather than a plausible cover.