Sure—so long as you don’t mind your bikes made entirely of acrylonitrile butadiene styrene.
That’s the only substance you can use in the leading desktop 3-D printer, the MakerBot Thing-O-Matic. Others intended for home use rely on similar types of plastics. (Industrial 3-D printers, in contrast, can handle a wider array of materials—more on those below.)
These substances share a number of virtues, including being relatively cheap, widely available, flexible, and durable. They’re great for making custom mobile-phone holders and sad Keanu Reeves dolls. But most useful items require more than one material.
Even a rudimentary bike needs rubber for the tires, foam and vinyl for the seat, a lightweight metal for the frame. Home 3-D printers can’t do that today. Nor can they do anything with organic-based substances like cotton, wood, or food. Someday they might, but even then it’s not clear whether they’d be able to approach the quality and cost-efficiency of mass-producing bikes or T-shirts.
Wide-eyed futurists foresee product shipping—nay, consumerism—rendered obsolete, because you’ll be able to make anything in your living room. All you need is a 3-D printer! Well, that and all the raw materials in the world, from silk for scarves to rare-earth metals for electronic gadgets. And you thought keeping your 2-D Deskjet stocked with ink cartridges was a pain.