Or: how to quickly turn an idea into a prototype
I don't know about you, but I'm always coming up with ideas for useful gadgets that can make my everyday life easier. Recently, this happened while I was tidying up my bathroom a bit: I noticed that there wasn't really a suitable place for my electric toothbrush in front of the sink that was close to the outlet.
The solution to this was obvious, I thought. I needed a new shelf. Anyone who lives in a rented apartment knows that drilling into a tiled wall always raises my blood pressure a bit. So I thought a little further and came up with the following idea: how about a mini shelf that can be attached to the wall using a Schuko plug and the wall socket?
After some discussion and, thanks to the positive feedback from my girlfriend and friends, becoming very convinced of my own idea, I asked myself: How can I implement something like this quickly and inexpensively? Given that I'd been planning to try something with 3D printing for a while, the method of choice quickly became clear to me.
Decision on a manufacturing process
Anyone who does a little research on 3D printing online will quickly discover that there are various 3D printing processes. For an overview of the different processes, I recommend this article on additive manufacturing by MEDtechler Lars: Additive Manufacturing – Lars Gerboth.
Which process you choose depends primarily on the material you're printing from. In my case, it was clear to me that I needed a plastic that could also insulate against the electrical voltage of the socket. It also had to be inexpensive.
Given these constraints, I opted for the simplest process, called FDM (Fused Deposition Modeling), in which molten plastic is layered through a nozzle to create a filament structure. A major disadvantage of this process is that particularly small structures cannot be printed with as high a resolution as with other processes. However, this didn't bother me much in my use case; structures down to 0.2 mm can still be reproduced well.
Decision on a CAD tool for designing the component
For me, this was one of the most interesting questions in the whole endeavor. Unfortunately, I have very little experience in component design, and this is limited to 2D drawings. What I do have, however, is a lot of experience in developing code. And this is precisely what drew me to the tool. OpenSCAD which allows you to “program” 3D drawings using a simple syntax.
So I can recommend it to anyone who comes from the programming world and wants to experiment with 3D models. By the way: OpenSCAD is freeware under the GNU General Public License, so it's free for everyone! Another gimmick is that the code can be managed and versioned with Git. A cheat sheet with the most important commands for OpenSCAD can be found here. here.
Of course, there are numerous other tools that can be used to create 3D models. Many of them are paid, some are free. For a deeper dive into the topic, I recommend this Article.
Structured approach to implementing a design
Unfortunately, a good design doesn't just fall from the sky. For any technical application, it's essential to consider the product's requirements in advance. For the "functional" requirements of a CAD design, in less complex cases, a small, hand-drawn sketch can be used, for example, to which dimensions can be added. This is especially useful for later, when performing a small preliminary validation on the computer before printing (see below).
In my case, I downloaded the dimensional drawings for the Type-F Schuko plug from the web and also created a few small 2D sketches in Visio, so I ended up with about two A4 pages of sketches that I could use as a "quick sketch" for my plug. Now it was time to finally get started with the design in OpenSCAD.
A few tips on design for additive manufacturing
The most important tip for optimizing design for additive manufacturing stems from the fact that you can't print "in the air." For all surfaces of a component that cannot be supported downwards in some way, so-called support structures are required. These structures serve no function other than enabling printing, thus resulting in increased material consumption and increased printing time.
This drives up the printing costs. After printing, these structures can usually be easily broken out or removed. I didn't take this into account for my initial design, which resulted in 30% of the material used during printing being support structure. So, how do I identify areas that require support structure? Basically, you have to imagine how the printer prints the model. Material is applied from the bottom up.
If there are surfaces that protrude laterally from the rest of the component or span a cavity, support structures are necessary for their printing. In some cases, support structures cannot be avoided, but in others, the design can be adjusted, for example, by using acute angles. The rule of thumb here is that surfaces inclined at approximately 45° above the printer floor can be printed well without support structures.
Another – more general – tip is to avoid over-dimensioning your design. As already mentioned, material quantity and printing time are the biggest cost drivers. So, it's worth considering which geometries are best suited to saving material.
From design to print
Now that you've come up with a decent design, you'll naturally want to print it. But don't be too hasty. Printing costs both time and money, and before printing, I recommend doing a quick pre-validation of the design on your computer. Unfortunately, OpenSCAD doesn't have a built-in measuring tool, so I downloaded the free Microsoft tool "3D Builder" from the Microsoft Store (here's a Link to the tool).
With the 3D Builder, mesh files in .stl format (the target format from OpenSCAD) can be imported, modified and measured.
To do this, render the design in OpenSCAD and export it in .stl format. Then, you can import the .stl file using the import function in 3D Builder (important: select the correct unit of length! This must match the unit used in the design tool; millimeters are the default in OpenSCAD).
Now select the measurement function under "Object" and use it to measure the "Quick Spec" (see above). Once you've confirmed that the design meets the product requirements, it's time to print!
The pressure
Anyone who thinks you need a dedicated printer for 3D printing is mistaken. I see three ways to get a print without owning your own 3D printer:
- Printing in an online printing house
- Printing in a makerspace or FabLab
- Printing from a friend who owns a 3D printer
I strongly recommend not printing your first prototype at an online print shop, but rather printing it yourself. There are several reasons for this: first, because printing at an online print shop can be very expensive, and the first design is prone to failure.
Second, because I think it's important to go through the process yourself to better understand the process. A third reason is that it speeds up the printing process. And finally, because it's simply fun 😊 There's nothing wrong with using an online supplier for larger batches (then the unit price also drops), but I wouldn't do that until a validated model is available.
Personally, I was at FAU for my first print Fab Lab from the University of Erlangen (thanks again for the kind help). What I particularly liked is that there's always someone there who can provide instructions and support with printing. It's also relatively inexpensive: for a non-commercial print, you pay 18 cents per gram of material (cost price as of April 2024).
Regarding the process: the .stl file alone is of no use to the printer. It's important to first prepare your model for printing using a "slicer" tool. This means placing the model in a virtual space in the printer so that the printer knows which direction it should be printed.
Then you can fine-tune the parameters: important things include adjusting the filament thickness, the material thickness of walls, and the so-called "infill": this is the density with which volume is filled, so that less material is used (instead of completely filling a room with material, similar to a concrete wall, a structure resembling a wall made of bricks is used). What's cool is that when slicing, you often get an estimate of how long the print will take and how much material is used.
With the sliced model, you're now ready to go. You can usually load the model onto the printer using a USB stick and start printing. Before printing, it's important to check whether you have enough material available (you can do this by checking the filament spindle on the back of the printer).
I would also watch the printer for the first few minutes while it's printing to verify that it's actually printing as intended. Then you can cancel the print in time if it isn't.
Closing words on the 3D printing guide
Printing your own prototype is easier than you might initially think. It's important to follow a few design tips and get help with your first print. For your first prototype, printing in a makerspace or fab lab is a good option, as it's relatively inexpensive and there's always someone available to help. By the way: if you just want to try printing without having to create your own design, you can find a Thingiverse definitely a great template.
Contact us if you need a prototype for your next medical device. MEDtech Ingenieur supports companies from the initial idea to series production.