3. 3D Printing#
This week we had a formation on how to use a 3D printer. We learnt about how to use it, how to use a slicer to print a 3D object, but also about printing time, limitations and frequent problems.
A word about 3D printing#
Altough the first 3D printing took place in 1984 (what a coincidence), that technology really spread in the 2010’s with the printers becoming more and more accessible. It is now used by a wide variety of people: from the person wanting to 3D print for fun to the corporation 3D printing crucial pieces for their projects. 3D printers are particularly useful for prototyping as they allow scientists and engineers to create a model or prototype with very little time and resources.
How to 3D print something using PrusaSlicer#
You obviously need a 3D file to print. It can be your own creation (cf. module 2, CAD), or a file you downloaded from the internet, for example on Thingiverse.
We used the software PrusaSlicer, which goes with the Prusa 3D printers we use at the FabLab. When you open the software for the 1st time, you have to indicate all the printers you could use with the slicer. Every printer is of course from the Prusa brand. I selected every printer we have at the FabLab, meaning MK3, MK3S and MK3S+, each with a 0.4mm nozzle.
To view my spoon on PrusaSlicer, I had to export my file as a .stl file so it can be understood my the slicer. You can do that by pressing F7 in OpenSCAD. To open this file in PrusaSlicer, you have to click on Add from the grey toolbar you see above the plate.
One the file selected, it should appear on the plate, in green, just like this:
On the right board of the page, you have to select the filament you’re using so the machine will adapt its behaviour. We only use PLA filaments at the FabLab, so I selected the setting Generic PLA, but if you want to bring your own filament there are setting for the most commons ones. Note that ABS, ASA and PS filament usage is prohibited in the FabLab because these materials release nocive gases. Just above you also have to select the printer you will be using. If you print at the FabLab, you can check the model on the white sticker of each printer.
If you want to know the approximate time the printer will take, you can Preview your object by pressing Ctrl+6. You could just then export your file on a SD card and print, but I will teach you how to optimise your printing time while staying frugal (as always).
How to optimise your printing time#
There are multiple settings to reduce the printing time direcly in the slicer. You can see them on the right of your object in PrusaSlicer. First, there is the System preset. You basically choose the thickness of the slices. The thicker the slices, fewer the layers, faster the operation. easy huh ? Of course there is a price to pay: since the layers are ticker, your vertical resolution isn’t as good. But if its for a draft print or something, it spares your time. It is particularly useful when you have no details in the z-axis (vertical), for example if you print a column or a vertical tube.
You can also set the Infill of your object. It describes how much the interior of your object is filled with material (0-100%), and you can also modify the infill pattern. It gives more resistance and weight to your object, but it uses more filaments and the printing time is thus longer.
Note: Your object doesn’t gain any resistance above 35% infill. It just gets heavier and wastes filament.
Exporting the file as g-code#
You feel like your object is ready to be printed, you set everything like you wanted and you are ok with the printing time ? I think it is time for you to export your file! After you pressed Ctrl+6, you can click on Export G-Code, in the bottom-right of the page. You have to name your .gcode file, a file format understandable by the printer. Name your file however you want if you have your own SD card. However, if you share the SD card with other people, it is recommended to put your name in the file. You can now plug the SD card to your computer, copy the G-Code file on it, eject and unplug the card.
Let’s print!#
You’re in front of the printer. You heart is beating fast. “is everything going to be okay ?”, you’re thinking. But no time for worries, you have to print. If you follow the instructions here everything should work.
Check if the filament is indeed PLA, and watch out for any knots in the filament. If everything is good, clean the green plate using alcohol and tissues. Also, check if there are any plastic residues on the nozzle from previous printings. If there are some, don’t panic, once the nozzle is hot you’ll be able to remove them by pulling gently.
Plug the SD card on the left of the orange interface. The files on the card should appear on the blue screen. Use the orange button to select the file you want to print. The process just started! The machine is going to heat the filament, then calibrate, then it starts the printing. Just like the takeoff of a plane, the firsts layers are one of the riskier steps of the printing (the plasting could not stick on the plate, and your object would be faulty). Therefore, stay next to the printer during the first layers.
As you can see, this print is going pretty well!
Here is a little video of my first 3D print. It’s a parametrical test to define the sizes of the cross pin holes for the catapult, which I will explain more precisely below.
3D-printing limitations and issues#
3D printers aren’t dark magic; therefore some limitations and issues can happen if you don’t make your arrangements properly. Here are some of the most common limitations and issues, and a guide to avoid these problems.
Limitations#
The limitation I had to deal with the most is the overhang. If you’re printing an object with steep inclinations, your might have to add some support so it doesn’t collapse during the printing. The best mindset you can have when modelling an object with CAD is that you regularly think about the printing process. Is what I create going to be easily printable ? According to the answer you can modify parts of your object, change its orientation or separate it in multiple pieces, and assemble it after the printing. That is exactly what I did for my spoon (see module 2).
Another thing you have to keep in mind is the limitation regarding the thickness of your walls. It is obviously impossible to print a wall that is thiner than the nozzle of the printer you’re using. These are very tecnical limitations and I hadn’t to deal with them, but still it seemed important to me. Here is a table that summarises this limitation with a 0.4mm nozzle: | Wall thickness (mm) | Possible ? | |---------------------|--------------| | less than 0.4 | No | | 0.4 | Yes | | btw 0.4 and 0.8 | No | | 0.8 and more | Yes |
Issues#
I will mainly insist on one issue that happen the most frequently, even if it never happened to me: bad adherence on the green board. If your first layers don’t stick to the board, the nozzle will pull the whole structure with it, and this destroys your whole printing. A good adherence on the board is capital if you want your print to suceed. Therefore, it concerns specifically objects with a little base: if you print a pyramid for example, your going to prefer printing it on its large base rather than on its tip to avoid this problem. Something else you can do is to ask your slicer to print a raft or a skirt, basically a support structure to improve the adherence of your object.
The catapult#
If you read the module 2, you know that my team and I intended to build a catapult. Each piece we designed had something in common: a lego cross pin piece should pass in every piece. Maybe you’re not familiar with this lego piece ? It looks like this:
I also found the image on the right on internet: it shows the section on the piece and its standard dimensions ! It doesn’t give us the exact measures we have to print but we now have a clear idea of the dimensions we should put in our parameters cruxwidth and cruxlenght.
Determining the parameters#
There is a way we can determine the parameters so the holes have the perfect size: it’s a test bar. We can design a bar with multiple cross holes of different sizes, each time 0.1mm bigger for example. That way we can determine the hole that fits the best with the lego piece, and apply these dimensions to each of our pieces! That is what we did on the 3D printing exercice. We designed the bar on OpenSCAD and we printed it together.
Once it was printed, the only thing we had to do was testing every hole with the lego piece I brought to class. Conclusion? The 3rd hole fits the best! Not too small neither too large.
Constructing the machine#
The next days, we came back to the FabLab to print the 4 pieces we needed to build the catapult. Here they are, finally together:
The last step was to build a lego structure and assembling every piece so they make up a working catapult. A detail that was essential is that we had to push the ratchet against the wheel in some way. I had the idea to use an elastic. Here is the final catapult as well as a video of the testing:
As you can see, our machine still had a limitation: we can’t bend the spoon to much or the lego structure breaks; but we changed the structure and now we don’t have this problem anymore. We were surprised that the ratchet wheel system would work so well; but as expected the catapult can’t send heavy things really far. Another limitation I found was fatigue, but not from the compliant piece, as expected. The elastic we used was actually of poor quality and it’s tension started to decrease because it elongated itself. That’s ok because I have plenty of elastics like this, and I realised if I want to use it longer, I had to release the tension on the elastic when I stop using the catapult.