It has long been possible to make a gun at home. But what happens when it no longer takes knowledge and skill to build one?

It won’t be long before a felon, unable to buy a gun legally, can print one at home. Teenagers could make them in their bedroom while their parents think they are “playing on their computer.” I’m talking about a fully functional gun, where the schematic is downloaded free from the Internet and built on a 3-D printer, all with the click of a button.

Hit print, walk away, and a few hours later, you have a firearm. There are no background checks. No age limits. No serial numbers etched on the barrel or sales receipts to track the gun.

It might sound like science fiction, but 3-D printers are quickly becoming a consumer product. These printers, which now cost about $1,000, can print objects by spraying thin layers of plastic, metal or ceramics that are built up into shapes. Long used by industrial companies to make prototypes and parts, 3-D printers are becoming faster and less expensive almost weekly. One manufacturer, MakerBot, has set up a retail store in Manhattan. Chinese companies have started making them, and prices are falling to about $500.