3D Printing

Who am I?

Jeremy Guillette

Instructional Technologist

FAS Academic Technology

What is this?

jaguillette.github.io/3d-print-overview

Basic Mechanics

there is a hot glue gun thing*

Diagram showing the parts of a 3D printer that the plastic filament goes through. A stepper motor pushes the filament through a heat sink and into a hot end, from which it extrudes. — Source: Leapfrog 3D Printers

A general caveat here, most of the time I'm talking about Fused Deposition Modeling, also known as Fused Filament Fabrication because Stratasys trademarked the first one. This is the hot glue gun style that's the most common, cheap, and desktop-friendly kind of 3D printing. There are also Stereolithography (SLA, for Stereolithography Apparatus), which involves a laser selectively hardening a photoreactive polymer (or goop, if you prefer) to construct an object, and Selective Laser Sintering, which involves shooting a laser into some powder to selectively harden it. Anyway, in FFF printing, this hot glued gun apparatus is what makes the plastic malleable enough to be printed. The goal in any 3D printer is to make the plastic really hot, but only in the print nozzle, not before or after. I've even printed this cool model to help demonstrate how that works. There's this orange bit, which is the nozzle. The gray block would be connected to a heating element and temperature sensor, so that's what makes things hot. It's also connected to a heatbreak, which transfers some of that heat to the heatsink, which is designed to dissipate that heat. A lot of printers, including the one we have, have a dedicated fan for that heat sink to keep the plastic cool and solid before it enters the nozzle.

Materials

MatterHackers

There are loads of different materials that are used in 3D printing. The most common, and the easiest to work with, is PLA (polylactic acid), which is a plant-based plastic. There are also ABS (Acrylonitrile Butadiene Styrene), which is stronger, but benefits more from an enclosed print area for temperature and smell control; and PETG (Polyethylene Terephthalate Glycol), which is also stronger than PLA but doesn't smell bad or require an enclosure. It is, however, stickier when heated, so PETG models can come out with a bunch of strings in gaps in the model. There are filaments with different kinds of materials infused in them, from glow-in-the-dark components to wood to metal to carbon fiber. Different filaments have different temperature and nozzle speed needs, and some of the infused filaments can quickly degrade standard 3d printer nozzles. There's a lot of stuff that you can heat up and push through a little nozzle, but different materials will require different tweaks when preparing models for printing.

The hot glue gun moves in three-dimensional space

Image of a computer rendering of a Prusa i3 mk3 3d printer

So this hot glue gun thing can extrude plastic, but what allows us to 3d print models with precision is the apparatus that moves the print head around in 3d space. There are different approaches to this engineering problem, but I'm just going to point out how it works on the Prusa that we have. There are 3 axes that we care about, plus the need to move plastic into the hot end. All of this motion is accomplished with little motors. The file that goes to the printer, a gcode file, is a series of instructions to those motors, telling them how to move to layer plastic to create the object. Objects are created layer by layer, so even if there are multiple objects on the print bed, the printer just layers the whole thing within its print volume. If you think about it, it wouldn't be practical for the printer to print one object, then another, then another, because the extruder is so much larger than the printer, which would limit how you could build objects, and also, doing that wouldn't buy you anything more than the layer by layer method; if you want a single part quickly, print each one one at a time. If you want a bunch of parts without having to do a lot of work yourself, print them all at once and let the printer run for a day or two.

gravity exists

In summary:

We need to tell the printer how much to move each motor to print an object, taking into account logistical limitations

3d models

bounded shapes

Here's a more complicated viewer so I can talk about more complicated stuff. This is a model of a viking key that I scanned at the Harvard Art Museum. What I want to talk about is the mesh that makes up this model. You can see that it's made up of very tiny triangles when I zoom in. You'll also notice that I can swing the camera into the interior, and see it from the inside. The model is essentially a bounded region of space. I can turn on the view of the normals to show you that each polygon has a direction that it's "facing", enabling the model to have a defined interior and exterior. Good software usually deals with this well enough that you don't have to think about it, but it's one of the things that can go wrong with a model. If the wrong part of the model is "outside", or there isn't good agreement among the polygons on where that is, or if the polygons don't form a solid boundary around a space (the term for this is "watertight", so if a shape wouldn't hold water, it's not "watertight"), then the model can be problematic to print. The software that translates models into printer instructions can cope with some issues, but there's only so much that that software can do.

Common file formats

STL

OBJ

List of 3d file formats

Modeling software

Blender (FOSS)
Meshlab (FOSS)
Fusion 360

Slicers

I've mentioned that there is more software between the 3d model and the print job a couple of times, so now it's time to talk about that software. This is a class of software called a slicer, because it slices your model or models into thin layers that are also translated into motor movement instructions for your printer. However, this isn't like sending a paper to your printer, where you only have a couple of options. Preparing a model for printing can be very easy, but it can also be something that you spend a lot of time fiddling with. Fortunately, also unlike paper printers, slicers allow you to save print projects, so you can tweak and try again later. The output of a slicer is almost always a gcode file, which contains the instructions for the printer on how to move its motors around to print the model. On our printer, you can put that file on an SD card and print from the printer, or print through the Raspberry Pi that's connected to the printer via the web, as long as you're on the right subnet.

BASIC

Import model
Check material, layer height, and infill
Export gcode

Middlin'

Import model
Adjust model position, rotation, and scale
Add support options
Check material, layer height, and infill
Export gcode

Stare into the abyss

FAQs

Where can I find cool 3d models?

What about other kinds of 3D printers?

Formlabs has a pretty good guide on the three main 3D printing technologies: FDM, SLA and SLS.

What about 3d printed guns?

This Wired article is the most informative that I've read on the topic, and this Ars Technica article that draws from it has some additional context.

Do you have a series of links from a high-velocity course on digital manufacturing?

The 3D printing and scanning page from the MIT course "How to make almost anything" is heavy on links, light on context, and a useful reference for a wide variety of 3d tech.