When your favorite gadget of the future breaks, you might select a replacement model online, download its design file and make a true 3-D replacement on your home printer.< >More importantly, prices for 3-D printing machines have been falling rapidly, reaching $20,000, and the day is foreseeable when they will fall below $1,000 and become home appliances, says Phil Anderson of the School of Theoretical and Applied Science at Ramapo College in New Jersey. The results, he warned, could be economically "disruptive." "If you can make what you need in your own home quickly, then manufacturers become designers, with no...