For some time, I've been noodling with a post about what I think it's important to know about 3d printing. Basically, what I would like to have known when I started doing it. And here it is.
Making and Modifying Models
3d printing starts long before the printing. It starts with the design of a 3d model, just as regular, on-paper printing starts with creating a document or image. There are many CAD tools which can be used to produce such models. In the past year or two, the free tools I've used in the past have moved to on-line applications rather than downloadable local ones, including
Sketchup and
Tinkercad. For something more heavyweight, there's
Blender, which I've tried to use to little avail. The standard file format for use in 3d printing is STL (stands for stereolithography, which ironically is a completely different method of 3d fabrication than what most home 3d printers use).
Of course, you don't have to start from scratch. You don't even have to do any design work at all. There are plenty of places where you can download ready-to-print designs. I usually frequent
Thingiverse and
Youmagine. Designs downloaded form there can be sent to a printer without any modification on your end, or they can be used as the basis of your own designs.
CAD vs. CAM
STL files define a shape but are agnostic about how what you do with it (for example, the same tools you use to build 3d printable designs are also used for architectural modeling and creating items for 3d animation and games), so after the CAD stage of design (computer assisted design), there's the CAM stage (computer assisted machining). There are stand-alone pieces of software which do various parts of this task, but they're typically bundled with the same software used to control the printer.
Cura and
Repetier are excellent free tools for the job.
In preparation for printing, the shape is analyzed and a series of instructions designed for a specific tool are generated to physically produce it. This is sometimes called "slicing," since one of main operations is to cut the model horizontally into a series of two-dimensional slices. For example, a pyramid is approximately a series of successively smaller squares set atop one another. Most software allows you to change the settings for how your model is sliced and what other instructions are sent to the printer. Important settings include:
- Temperature. Your hot end (the heating element which melts the filament so that it can be extruded) has to be hot enough to get the plastic soft and flowing, but not so hot as to burn it. Different filaments work in different temperature ranges, and even within recommended temperature ranges, there can be better temperatures for specific brands and hot end designs.
- Thickness of layers. This determines the resolution of the printed piece in the 3rd dimension. For example, when printing out that pyramid, a 3d printer has to print out layers of finite height, so it can't do an unbroken slope, but it can print out a series of shorter or taller steps. The thinner the layer, or the shorter the step, the more closely it approximates that slope. Small values, measured in hundredths of mm, will give you very nice resolution, but take correspondingly longer.
- Shell thickness. This may be divided into top, bottom, and side thickness.
- Fill density. 3d printed items are usually not solid plastic. Rather, they've got an internal grid providing enough substance to hold together.
After some experimentation, I've found some default settings which I use nearly all the time. I print with PLA filament most of the time, which uses relatively low temperatures, so my hot end is usually set around 190-200C, with a layer height of 0.1mm (down to 0.05 mm if I want really high quality, up to 0.15 or even 0.2 if I'm OK with fast but coarse, or if the piece has very little detail and thick layers won't matter much), and 20-25% fill. Shell thickness on the sides is a function of the diameter of the printer's nozzle. That is, if you've got a 0.4mm nozzle, your shell thickness has to be in whole-number multiples of 0.4mm. A double-thick shell (say, 0.8mm with an 0.4mm nozzle) is usually pretty good, with top and bottom to match.
This process (CAM/slicing) generates a set of instructions telling your printer what temperature to heat up to, where to go, when to extrude filament and when to stop, and so forth, based on the design and other settings. These instructions are in a language called gcode. Those commands may look something like this:
G1 F1200 X180.564 Y50.739 E26.57755
G0 F4200 X181.130 Y50.739
G1 F1200 X181.759 Y51.369 E26.62196
G0 F4200 X181.759 Y50.803
G1 F1200 X181.696 Y50.739 E26.62644
G1 F1800 E25.62644
G0 F4200 X141.759 Y50.966
G1 F1800 E26.62644
G1 F1200 X141.533 Y50.740 E26.64239
G0 F4200 X140.967 Y50.740
G1 F1200 X141.759 Y51.532 E26.69827
However, you don't actually have to know anything about gcode to do 3d printing. The software handles it all for you, just as your printer drivers handle encoding data to send to your printer without you needing to understand the language in which it handles that conversation.
The Printer and Printing
At last, we look at the hardware itself. Most home and hobbyist printers do FDM (filament deposition model), which uses a plastic filament as its raw material (there's also DLP and SLA printing, which use a tank of photosensitive resin and various methods of exposing them to UV; these printers tend to be faster and more detailed, but the process is
vastly more expensive). You'll almost always find filament in 1 kg spools at with a diameter of 1.75mm or 3mm. Be sure to get the right size for your printer!
This filament is drawn through an extruder at a metered rate. A heating element in the extruder assembly heats the filament to a semi-liquid state, and it's forced through a nozzle onto a print bed.
I have no recommendations for specific models of printer. That landscape changes too quickly. But I do have some recommendations on what to avoid, what to get, and what to consider.
Things to be wary of include:
- Cheap kits. It's possible to get a very inexpensive DIY printer on Amazon and other retail outlets. They're not necessarily bad, but they do tend to be made by no-name overseas manufacturers. Some are perfectly good, but instructions may be incomplete or poorly translated, and if you've got a bad part, customer support may be weeks away. That may be tolerable for a second printer, when you've got a good idea of how and why things work and can potentially source replacement parts yourself, but it's a really good idea to go brand name for your first.
- Proprietary filament. Some manufacturers follow the inkjet printer model: sell you an inexpensive printer and make it back on the printing medium. The printer won't work with third-party filament. Instead, you have to use cartridges they sell at a substantial markup over "open source" filament.
Things to get:
- A heated bed. A common problem with 3d printing is bowing or curling. As the first few layers of filament cool, they shrink and peel away from the print bed, resulting in a print with a curved bottom. There are a variety of dodges around that, but by far the most effective is a heated bed. If the print bed maintains a temperature around 50-60C, those bottom layers don't cool to the point of shrinkage. Curling vanishes. No matter what it costs in addition to a basic model of printer, you'll more than make it back in savings on ruined prints.
- Accessories. There are a few consumables and other bits and pieces you'll need for good printing. You want kapton tape, for example. This is a plastic which stands up to high temperatures well. A layer of this tape provides a protective layer to your print bed, preventing gouges when you have to chisel off prints which are really stuck on, as happens some times. You'll also want an offset spatula, bench scraper, or similar thin metal item to do exactly that. Finally, you'll want some material to help prints stick to the print bed. Exactly what you need depends on the material you're using. If you're using PLA (see below for more discussion of filament materials), that's cheap hairspray. I use AquaNet or its generic equivalent. If you use ABS, probably the second most common filament, you need a bit of a slurry of acetone and some ABS dissolved in it. Nylon wants a porous surface like paper or cardboard. Check manufacturer's recommendations. And it can't hurt to have a few craft basics like an Xacto knife and fine sandpaper and the kinds of drivers, wrenches, and other tools you'd use on a computer.
Things to consider:
- Temperature range. A basic FDM printer can at least get up to the low 200s C, which is good enough to print in PLA. PLA, which is short for "polylactic acid," is the cheapest and most common 3d printing filament. It's a plastic made from corn. It's nontoxic and biodegradable and it's perfectly good for miniatures, game pieces, art pieces, and the like. It is not, however, either particularly durable or flexible, so it's not great for a good many practical applications. ABS, or acrylonitrile butadiene styrene, is what Legos are made out of. It's a much stronger, but it puts off an unpleasant odor when printing (so you don't want to be around), wants a heated bed (above) and higher temperatures, starting around 230C, if not hotter. And there are a variety of also-rans (nylons, polycarbonates, etc.) which print as hot as or hotter than ABS. Something that goes up to 230 is certainly good enough for PLA and maybe ABS. Up to 250 is good for ABS and potentially some other exotics, and something that goes up to, say, 280 can print in pretty much anything. If you're just want a starter printer, you don't need a seriously hot hot end, but if you're going into it knowing that you'll want to work in industrial-grade materials, then higher temperatures are a must.
- Extra nozzles. The nozzle on your printer can and eventually will get clogged up and need to be replaced, so it's a good idea to start out by getting one or two extra for when you need it. What's optional is buying nozzles in different sizes. Most printers come with a nozzle with a diameter of around half a millimeter. That's essentially the size of the "line" it draws when it prints. A different nozzle, then, effectively changes the "resolution" at which the printer prints. For very fine work, you may want to use an 0.3mm or 0.2mm nozzle (I've worked with nozzles as small as 0.1mm, but it was painful to work with), while for large pieces, a larger nozzle can get the job done faster (I printed parts for what was ultimately an 18" tall sculpture with a 1mm nozzle and it came out just fine).
- Print volume. This is one of those "get what you pay for" things. Smaller printers are cheap, and bigger printers are more expensive.
