3D Printing 101: Materials, Layers, and Supports

3D printing is the one big new skill this month, and it is worth learning properly because it will serve you long after TARS. Every part of the robot's body comes off your printer, so before you print anything real, you need to understand what the machine is actually doing and the handful of settings that decide whether a part comes out strong and clean or weak and warped.

Your printer builds an object by melting a plastic filament and pushing it through a hot nozzle, drawing one thin horizontal layer at a time. When a layer is finished the nozzle lifts a fraction of a millimeter and draws the next layer directly on top, and the two fuse together as the plastic cools. A tall part is simply hundreds of these slices stacked up. This layer-by-layer nature has one important consequence: a printed part is strong across a layer but weaker between layers, so the direction a part is printed in changes how strong it is. That is why the TARS files come already rotated a particular way, and why you should leave that orientation alone rather than turning parts to suit yourself.

The three plastics, and why the choice matters

You will work with three filaments this month, and they behave very differently. PLA is the easiest to print and quite rigid, but it is somewhat brittle and softens in heat, so a PLA part left in a hot car can droop. PETG is tougher, less brittle, and more heat-resistant, which is exactly why TARS's body is meant to be printed in PETG: a robot with servos that generate heat and joints that take repeated stress needs the extra durability, and a brittle body would crack over time. TPU is a different animal entirely, it is flexible, like a firm rubber, which is why TARS's footpads are printed in TPU so they grip the floor and cushion its movement. Choosing the right plastic for each part is a real engineering decision, and it is the same match-the-material-to-the-job thinking you will use everywhere in making.

Layer height, walls, and infill

Three settings do most of the work in trading off strength, appearance, and time. Layer height is how thick each slice is: a thinner layer such as 0.2 millimeters gives smoother surfaces and bonds well but takes longer, while a thicker layer prints faster but looks coarser. Walls, also called perimeters, are the solid outer shells of the part; more walls make a stronger, less hollow object, and three walls is a common sweet spot for durable parts. Infill is the internal lattice that fills the inside, given as a percentage, and it is where a lot of the part's strength and weight comes from. You almost never print solid, because it wastes plastic and time; around 20 percent infill is a good balance, and a gyroid infill pattern is popular because it spreads strength evenly in every direction rather than favoring one axis. Together these three numbers decide how solid, how pretty, and how slow a print is.

Supports and the first layer

Because the printer builds upward and cannot print into empty air, any part that overhangs steeply needs support material: temporary scaffolding printed underneath the overhang that you snap off afterward. Tree supports are a branching kind that use less plastic and come off more easily than solid blocks. The TARS parts are pre-oriented to minimize supports and to keep the visible surfaces clean, which is another reason not to rotate them yourself.

If you remember one thing from this lesson, make it this: nearly every failed print fails at the first layer. If that first layer does not stick flatly and evenly to the bed, the part lifts, warps, or turns into a bird's nest of stringy plastic. Good adhesion comes from three things: a level bed (which you set up last lesson), the right temperature, and a clean plate free of grease and dust. Get in the habit of watching the first layer of every print go down; if it is laying flat and sticking, walk away confident, and if it is not, stop and fix it before you waste hours of filament.