How Does a 3D Printer Work?

There is a lot of excitement building around what 3D printers can and might do. But how does a 3D printer work? It’s actually not very complicated.

Here are the mechanics behind the most common consumer-level printers that extrude plastic.

In goes filament, out comes gooey plastic

3D printing filament

3D printer owners choose between two types of plastic: acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA). Some printers work with just one, other printers work with both. The plastic comes as strands of filament that are usually a standard 1.75 millimeters or 3 millimeters in width.

ABS, which is used to make Legos, is chemical-based and works at slightly higher temperatures. PLA is derived from natural sources, such as corn or sugarcane. It’s more rigid and glossy than ABS. Outside of 3D printing, it can be used to make compostable packaging.

Filament, which is usually stored on a spool attached to a 3D printer, can be expensive. MakerBot charges $48 for 2.2 pounds of PLA, though PLA or ABS can be had for half the price on eBay. The company estimates one 2.2 pound spool of filament is enough to print 392 chess pieces.

The price is likely to drop as 3D printers become more common and filament is manufactured on a larger scale. One current way to drop the cost is to use a filament extruder; you feed in cheaper plastic beads or recycled plastic and out comes strings of filament.

Once you’ve obtained the filament, it is fed into the 3D printer’s print head. Generally, this is a boxy shape with a nozzle sticking out of it.

Type A Machines Series 1 Pro 3D printer

A gear pulls the piece of filament through the print head. Just before it is extruded by the pointed nozzle, the filament passes through a heated tube and liquifies. The nozzle deposits it in ultra-fine lines generally about 0.1 millimeters across. The plastic solidifies quickly, sealing together layers.

ABS generally needs to be printed on a heated surface; otherwise, the bottom layer of plastic curls up. PLA can be printed on a non-heated surface.

Most printers have one print head, which means objects are printed in one color, or the filament has to be switched out during the print job. Some printers, such as MakerBot’s newest, the Replicator 2X, have two print heads. This allows objects to be printed in two different colors.

Back and forth, layer by layer

3D printing is additive manufacturing. That means the plastic is built up one layer at a time.

A 3D printed dragon head. Photo by Signe Brewster

MakerBot

Other 3D printers like RepRaps, the open source DIY printers that started the consumer 3D printing trend, sometimes work slightly differently. The print bed may move up, down, forward and backward while the print head only moves side to side. Or there are more unusual systems, such as the DeltaMaker, where the print head moves in three dimensions.

Print jobs can take minutes, hours or days, depending on the size and density of an object. For example, artists recently ran seven Type A Machines Series 1 printers for two months straight to build a 10 x 10 x 8 foot sculpture.

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