A practical guide to 3D printing

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.

I can therefore recommend this 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 and therefore free for everyone. Another nice feature is that the code can be managed and versioned using Git. A cheat sheet with the most important commands for OpenSCAD can be found [here/below/etc.]. on-line.

On the left you can see the code editor, on the right the preview window.

In addition, numerous other tools exist that can be used to create 3D models. Many of these are paid, while some are free. To delve deeper into the topic, an overview of various options is recommended. CAD programs.

Structured approach to implementing a design

Good design doesn't just fall from the sky. As a general rule, any technical application requires careful consideration of the product requirements beforehand. For the functional requirements of a CAD design, a small, hand-drawn sketch with dimensions can be used in less complex cases. This becomes particularly useful for performing a preliminary validation on the computer before printing.

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 that in the end I had about two DIN A4 pages of sketches available, which could serve as a "short specification" for my plug. Now it was finally time to start with the design in OpenSCAD.

A few tips on design for additive manufacturing

The most important tip for optimizing designs for additive manufacturing stems from the fact that you can't print "in mid-air." For all surfaces of a component that cannot be supported from below in any way, so-called support structures are required. These structures serve no function other than enabling the printing process. This increases material consumption and printing time.

This drives up the printing costs. After printing, these structures can usually be easily broken or removed. I didn't consider this for my first design, which resulted in 30 % of the material used in the print being support structures.

So how do you identify areas that need support structures? Basically, you have to imagine how the printer creates the model: material is applied from the bottom up.

Therefore, if there are surfaces that, for example, protrude laterally from the rest of the component or span a cavity, support structures are necessary for printing them. In some cases, support structures are unavoidable. In other cases, the design can be adapted, for example, by using sharp angles. A rule of thumb is that surfaces with an incline of approximately 45° above the printer bed can be printed well without support structures.

Another, more general tip is to avoid over-engineering your design. Material usage and printing time are the biggest cost drivers. Therefore, you should consider which geometries are suitable for saving material.

From design to print

Once you've arrived at a decent design, you'll naturally want to print it. But don't rush into it: printing costs both time and money. Before printing, it's advisable to do a quick preliminary validation of the design on your computer.

Unfortunately, OpenSCAD doesn't have a built-in measurement tool. Therefore, I downloaded the free Microsoft tool "3D Builder" from the Microsoft Store: Link to the tool.

You can use 3D Builder to measure the model, as such a tool unfortunately does not exist in OpenSCAD.

The 3D Builder allows you to import, modify, and measure mesh files in STL format.

Here's how to proceed: Render the design in OpenSCAD and export it in STL format. Then, you can open the file in 3D Builder using the import function. It's important to select the correct unit of length. This must match the unit used in the design tool; in OpenSCAD, the default is millimeters.

Now, under "Object," you can select the measurement function and use it to check your short specification. Once you've confirmed that the design meets the requirements, you can proceed to printing.

The pressure

Anyone who thinks you need your own printer for 3D printing is mistaken. There are several ways to create a print without owning a 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 the first prototype at an online print shop, but rather printing it yourself. There are several reasons for this.

Firstly, printing at an online print shop can be expensive, and a lot can go wrong, especially with the first design. Secondly, you learn the process better by going through it yourself. Plus, you often get your print job done faster. And last but not least, it's simply fun.

For larger quantities, an online provider can be quite useful later on, especially if a validated model already exists.

I personally experienced my first pressure in FAU FabLab Created by the University of Erlangen. I particularly liked that there's always someone on site to give instructions and help with printing. The price is also relatively inexpensive: For non-commercial printing, you pay about 18 cents per gram of material (cost price, as of April 2024).

Regarding the process: The STL file alone is not sufficient for the printer. The model must first be prepared using a so-called "slicer" tool. This positions the model in a virtual space within the printer, so that the printer knows the correct orientation for printing.

Fine-tuning can then be carried out, for example:

• Filament thickness
• wall thickness
• Infill (fill density of the material inside)

Slicing usually provides an estimate of how long the print will take and how much material will be needed.

The slicer tool translates the model "into the printer's language." The infill of the walls can also be seen in the section view.

With the sliced model ready, you're finally ready to start. The file is often transferred to the printer via a USB stick. It's important to check beforehand that you have enough filament.

It is also advisable to monitor the first few minutes of printing to ensure everything is running correctly. If not, the printing process can be stopped in time.

Closing words on the 3D printing guide

Printing your own prototype is easier than you might initially think. It's important to keep a few basic design tips in mind and to get some help with your first print.

A makerspace or FabLab is particularly suitable for the first prototype, as it is relatively inexpensive and usually offers competent support.

Those who want to try printing without creating their own design can find options on platforms such as... Thingiverse numerous templates.

Feel free to contact us if you need a prototype for your next medical device. MEDtech Ingenieur supports companies from the initial concept to series production.