Comment by Mashimo

Most of the shelf 3D printers just read g-code: https://all3dp.com/2/3d-printer-g-code-commands-list-tutoria...

Simplified they just get thousands of commands from which position to which position to move a toolhead, at what speed and how much plastic to extrude.

They would have to re-create the 3d model from those commands and compare them to banned ones? But then the firmware is often open source or at least can be flashed. And also how would the printer know if it's a toy gun or a real gun? Or just a part for a gun.

Paper printers / copiers refuse to copy money because the government controls the source, the paper money. They add small dots on them.

The government can't add those dots to self made 3d models.