How Does a 3D Printer Work?

A 3D printer builds a real object from a 3D file by making it one thin layer at a time. The most common kind, a filament printer, melts a plastic string and draws each layer with a hot nozzle, the way you’d draw with a hot glue gun. A resin printer does it with light, hardening a liquid layer by layer. Stack a few hundred layers and you’re holding a keychain, a phone stand or a rocket.

Printing at home or at school? Read the 3D printer safety checklist first. Buying a first printer for a student? See our first-printer picks.

The big idea: building in layers

Most ways of making things take material away. A woodworker carves a block, a machine drills metal. A 3D printer does the opposite: it only adds material, and only where the object needs it. That’s why 3D printing is also called additive manufacturing.

Here’s a way to picture it. Take a stack of paper and cut each sheet to a slightly different outline. When you stack the sheets back up, the edges form a shape. A 3D printer does the same thing, except it makes its own “sheets” out of melted plastic or hardened resin. A typical layer is 0.2 mm thick, about as thick as two sheets of printer paper, so even a small toy is a pile of hundreds of layers.

Makers in our network print everything from keychains and cookie cutters to holders, mounts, vases and cosplay helmets. Every one of them was built this way, layer on layer.

From idea to object in your hand: 6 steps

1. Start with an idea. A name tag, a pencil holder, a replacement knob for a drawer. Simple shapes are the best first prints.
2. Make or find a 3D model. A 3D model is the object’s shape saved as a file, usually an STL. You can design one for free in your web browser with Tinkercad (see our beginner’s guide to Tinkercad) or download one someone else made (where to find 3D files). Our guide to 3D printing file types explains STL, 3MF and the rest.
3. Open it in a slicer. A slicer is a free program that cuts the model into layers and plans every move the printer will make. You pick your printer, the plastic and how thick the layers should be. If the model comes out the wrong size, here’s how to scale it.
4. Save the G-code. The slicer turns its plan into G-code, a long list of directions the printer can follow. Our STL to G-code guide walks through this step in each slicer.
5. Print it. Send the file to the printer over Wi-Fi or on a USB stick or SD card, then watch the first layer. If the first layer sticks flat and even, the rest usually goes fine. Small prints take under an hour, big ones a day or more (see how long 3D printing takes).
6. Finish it. Let the plate cool, pop the part off, and snap away any supports, the throwaway scaffolding the printer adds under parts that would otherwise print in mid-air.

How does a 3D printer know what to print?

It doesn’t, really. A 3D printer never “sees” your rocket. It just follows directions, thousands of them, one line at a time. The slicer writes those directions in G-code. A real line looks like this:

G1 X90.6 Y13.8 E22.4

• G1 means “move in a straight line.”
• X90.6 Y13.8 is where to go: 90.6 mm across and 13.8 mm back on the build plate, like a point on a graph.
• E22.4 tells the extruder to push filament while it moves, so the nozzle leaves a line of plastic behind it.

Other lines set the nozzle temperature, switch the fan on, or lift the nozzle up to start the next layer. A small print can have tens of thousands of these lines, and the printer works through them one by one. This is also why G-code only works on the printer it was sliced for: the directions assume that printer’s size and parts.

The parts of a 3D printer

Almost every printer in our network is a filament printer, and it’s the kind you’ll most likely meet at home, at school or at a library. Here are its main parts:

• Filament spool: a reel of plastic string, usually 1.75 mm thick. The most popular plastic is PLA, made from plants like corn or sugarcane. (Picking one? See our PLA guide and PETG vs PLA.)
• Extruder: two small gears that grip the filament and push it forward, a little at a time.
• Hotend and nozzle: a heater melts the plastic and squeezes it out of a tiny brass nozzle, usually 0.4 mm wide. For PLA the nozzle runs at about 190–230 °C (375–445 °F), far hotter than boiling water.
• Build plate (or bed): the flat surface the print is built on. It’s usually heated, roughly 35–60 °C (95–140 °F) for PLA, so the first layer sticks. The right numbers are printed on your spool’s label.
• Cooling fan: blows air on the fresh plastic so each layer hardens before the next one lands on it.
• Frame and motors: small motors move the nozzle and the plate to exactly where the G-code says.

What happens at the tip of the nozzle

The nozzle presses each line of melted plastic slightly into the layer below it, so the two fuse together as they cool. Inside a solid-looking print is usually a honeycomb or grid pattern called infill. It keeps the part strong while saving plastic and time.

How it moves: X, Y and Z

Printers move in three directions, the same ones you’d use on a graph: X is left and right, Y is front and back, and Z is up and down. Each layer is drawn using X and Y. When a layer is done, the printer steps up in Z by one layer and starts the next.

On many beginner printers the nozzle moves left and right while the bed slides front and back. Faster printers, called CoreXY printers, move the nozzle in both directions and keep the bed still except for lowering it one layer at a time.

Thin layers or thick layers?

Layer height is how thick each layer is. Most prints use 0.1 to 0.3 mm, and 0.2 mm is the usual starting point. Thin layers hide the “stair steps” on curves but need more layers, so they take longer. Thick layers print faster and show more lines. A layer also can’t be much thicker than the nozzle is wide: with a 0.4 mm nozzle, about 0.3 mm is the practical limit.

Resin printers: printing with light

A resin printer has no hot nozzle. Instead it has a shallow tray, called a vat, filled with liquid resin that hardens when ultraviolet light hits it. Under the tray sits a screen, a lot like a phone screen, with UV lights behind it. For each layer the screen shows a black-and-white picture of that layer, and light only gets through where the picture is white. Those spots of resin turn solid.

The build plate dips into the resin from above, the screen lights up one layer, then the plate lifts a tiny bit and the next layer hardens underneath. That’s why resin prints come out upside down. The layers are very thin, often 0.025 to 0.05 mm, so resin prints show fine detail, like faces on miniature figures.

There’s more work after the print: the part gets washed in alcohol (or water, for water-washable resin) and then cured under UV light to finish hardening. Liquid resin can cause skin allergies, so resin is for adults to handle, with gloves and safety glasses (see the safety checklist).

Filament or resin?

For a first printer, especially one a younger maker will use, filament is the simpler and cleaner choice. Our resin vs filament guide goes deeper.

The 7 kinds of 3D printing

Engineers sort 3D printing into seven families (in a standard called ISO/ASTM 52900). You’ll meet the first two at home and at school; the rest are mostly found in factories and labs.

• Material extrusion: material is pushed out of a nozzle. This is the filament printer (also called FDM or FFF).
• Vat photopolymerization: light hardens liquid resin in a tray. This is the resin printer (SLA, MSLA or DLP).
• Powder bed fusion: a laser or heat melts selected spots in a bed of fine powder, layer by layer.
• Binder jetting: a print head sprays glue onto powder to stick each layer together.
• Material jetting: tiny droplets are sprayed and hardened, much like an inkjet printer printing in 3D.
• Directed energy deposition: a laser or electric arc melts metal as it’s fed in, often to build up or repair big metal parts.
• Sheet lamination: thin sheets of paper, plastic or metal are cut and bonded into a stack.

Try it yourself

You don’t need to own a printer to make your first 3D print. Here’s a path that works from anywhere:

1. Design something simple in Tinkercad. It’s free and runs in a web browser. Start with a name tag: a flat box with raised letters on top. Students under 13 can join through a teacher’s class or with a parent’s OK. Our Tinkercad guide shows the first steps.
2. Or find a ready-made model in a free model library (our list).
3. Check the size. Measure it against something real, like a ruler or a coin. Our free in-browser scaler can fix a model that comes out tiny.
4. Find a printer. Many schools and public libraries have one you can use, and some libraries print through Intagly. Or a parent, teacher or other adult can send your file to a maker in our network to be printed and shipped.

Have an idea but no 3D model? An adult can start a free chat with a designer in our network, who can turn a sketch or photo into a printable file: talk to a designer.

Buying a first 3D printer: picks for parents, teachers and adult beginners

If you’re choosing a printer for a student or for yourself, two things matter most for a beginner: the printer should calibrate itself (no hand-leveling the bed), and it should come with a slicer that just works. All three picks below do both. They’re from Bambu Lab, the brand we see most often in our maker network.

Comparing more printers? See our best 3D printers under $300 and best 3D printers for schools.

FAQ

How does a 3D printer know what to print?

It follows G-code, a list of directions written by a slicer program. Each line says where to move and how much plastic to push out. See the 6 steps above.

How long does it take to 3D print something?

A keychain can take 15 minutes; a helmet can take a few days. Size, layer height and speed matter most. Our guide to how long 3D printing takes explains why.

Is 3D printing safe for kids?

Filament printing can be, with an adult nearby, good airflow and hands kept away from hot and moving parts. Resin printing is for adults to handle. See the safety checklist.

What age can you start 3D printing?

Designing can start young: Tinkercad accounts for students under 13 go through a teacher or a parent. Running a filament printer works best with an adult close by. Resin handling is for adults.

What is 3D printer filament made of?

Plastic. The most common, PLA, is made from plants like corn or sugarcane. Others include PETG (tougher), TPU (bendy) and ABS (handles heat). See our filament guide.

Can a 3D printer print anything?

No. It can only print shapes that fit inside it and that can be built from the bottom up, and only in the materials it can melt or harden. Overhangs need supports, and very thin walls may not print.

Do I need to know how to design to 3D print?

No. Millions of free models are ready to download (where to find them). When you want something of your own, Tinkercad is an easy place to learn.

Is 3D printing the same as additive manufacturing?

Yes. Additive manufacturing is the industry name for building objects by adding material layer by layer, which is exactly what a 3D printer does.

3D printing words

• Additive manufacturing: making things by adding material layer by layer; another name for 3D printing.
• Build plate (bed): the flat surface a print is built on.
• Cure: to finish hardening a resin print under UV light.
• Extruder: the gears that push filament into the hot nozzle.
• Filament: plastic string on a spool that a filament printer melts.
• G-code: the list of directions a printer follows, line by line.
• Infill: the hidden pattern inside a print that makes it strong without being solid.
• Layer height: how thick each layer is, often 0.2 mm.
• Nozzle: the tiny hot tip the melted plastic comes out of, usually 0.4 mm wide.
• PLA: the most popular filament plastic, made from plants.
• Resin: a liquid that turns solid under UV light.
• Slicer: the program that cuts a 3D model into layers and writes the G-code.
• STL: the most common 3D model file type.
• Supports: throwaway scaffolding printed under parts that would otherwise hang in the air.