3D printing is a fairly complicated procedure, today we're going to focus on taking an existing 3D model and preparing it for the 3D printer. That process is refered to as "slicing" a 3D model, and we use the free and open-source software cura.
The process of slicing converts a "mesh" (mostly commonly an .stl file) into a
"tool path" (most commonly a .gcode file). A tool path file tells the machine
exactly what motions to make, how much plastic to extrude, what temperature to
be at, etc.
We're mostly going to be focused on that "slicing" process today, as designing files for 3D printer is a very broad topic.
Gcode files have ultimate control over the machine, a malicious gcode file could cause the machine to tear itself apart, as it tries to print outside of the bounds of what is physically possible. Of course many printers implement safeties to prevent the more common ways a machine could damage itself, but such measures are never perfect.
It's very important that you use the right machine profile in cura, otherwise
the printer won't work properly and, in the worst cases, could damage itself.
The "Dwmaker" printer we use in the crafty fox uses the profile of the
ultmaker 2 extended +.
It's also important to remember that this is a physical machine, it can burn you, it can catch on to clothing and flesh, or otherwise do damage to actual humans. That being said it is safer than a drill or even a knife, just keep your hands out of the work zone while it's running and don't touch any of the hot surfaces unless you've verified that it's safe to do so.
The material we use to 3D print is called "filament", there are a number of different varieties with different material properties, but the one we use most in the shop is "PLA", or "poly-lactic acid". It's a bioplastic most commonly made from corn, although any plant starch will do.
Previously the primary plastic used for 3D printing was ABS, in addition to being more enviromentally friendly PLA has mechanical properties that make it better suited for 3D printing. Most notably minimal thermal-expansion, this means that the prints don't warp very much when they cool down. Hopefully that kind of warping, and how to work around it, is something you never need to worry about.
PLA is available in a variety of colours, but of course the printer can only deal with a single roll of filament at a time, meaning that you can't mix different colours/filaments in one print.
Filament comes in two common variaties, 3mm and 1.75mm. We use 1.75mm in our shop.
Printing is subject to the square-cube law, so an object that's twice as big actually takes 4 times as much filament, weights 4 times as much, and takes 4 times as long as a normal sized print.
Cura has a handy scaling function you can use to change how big an object is.
I use yeggi as a search engine specifically for 3D models.
Not all 3D models are actually printable, but most of the ones on sites yeggi links to are. The first thing you should check is if someone actually has printed that model. If you don't see a picture of the finished product, well it's possible that the model wasn't designed to be printable. Assessing how easy it is to print a given model is an important skill.
There are two main ways a 3D file can fail to be printable.
Sometimes people will try to print a 3D file from a game, or that we otherwise designed to just be shown on a computer screen. Those types of files don't need to be physically possible, the most obvious example is that things can be zero-width, be literally infinitly thin. In order to explain fully explain the ways a mesh can be broken I'd have to spend time explaining how computers actually render 3D graphics, suffice to say that a 3D file designed to be pretty on a screen are completly different from 3D models designed to by physically real objects, even though they use the same file format.
We commonly say meshes like this "aren't water tight". If you're not sure, you can look up a tutorial on "making sure a mesh is water tight".
You can't print things in mid-air, but how close can you get? It's generally recomended that you don't make overhangs that are much more than a 45 degree angle. Tall/thing spires can also be a problem, as often the layer beneath has not had time to cool down before you start printing the next layer. It's also important that your print has lots of contact with the 3D printer bed, too little and you may find your print has become detached in the middle of a print.
The only real way to get a feel for this though is to try a bunch of prints and see what gives you a hard time.
Cura has many parameters you can change and tweak in order to change how the printer produces your object. There are thousands of options to tweak, but only a handfull that actually matter in the day-to-day operation of the print.
One import option is layer-height. If you look closely at a 3D print you'll notice
that it has a "grain" to it, you make that grain finer (and increase the qaulity
of the 3D print) by reducing the layer height. Of course doing that means the
print will take longer to finish, as there are more layers to actuall print. You
can also go the opposite direction, increasing the layer height for faster
printing if you're going to be sanding or painting the print, or even just if a
bit more noticable of a grain isn't a problem.
Another important option is support material. Support material adds
sacrificial support to your prints so that you don't have to print in mid-air if
you have a large overhang. I recomend avoiding it if you can, as it can be hard
to remove. It's especially hard to remove if it's supporting fine detail, as you
can accidently damage the print as you try to remove it.
3D printed objects are semi-hollow. Infill percentage determines exactly how hollow it is, and increasing the infill percentage will make a part stronger, although it will use more time and filiment.
You can also change the "shape" of the infill, normally it fills it in with a loose mesh of squares, but you can change it to be triangles, or more complicated 3D shapes.
As near as I can tell these don't have much real effect on the structural integrity of the prints...
The number of walls has the biggest affect on strength, vase mode only works for a specific shapes but can produce very nice results very quickly, if your shape is single walled and has the right topology. You can enable variable layer height to get many of the drawbacks of high and low layer heights at the same time. Ultimaker has spent a lot of time making their default printing profile rock solid, but there are many setting that are intended to affect the performance of the printer.
Copyright 2019-2023 Alex Davies
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