You wouldn't print a modular case

When experimenting with different eurorack setups you always have the dillema what size case do I get? If you get a small case it looks made to fit but leaves little to no room if you ever decide you want to add another module. On the other hand, if you buy a huge case you are left with all this dead space around the few modules you have in there. So I wanted to try and design my own case and 3D print it.

If you aren’t familiar with the format: eurorack is a standard for synthesizer modules introduced by Doepfer in the 90s, it's based on the rack standard using horizontal pitch (HP) and rack units (U) for width and height respectively. Modules are powered using ribbon cables from a (single) power supply unit, with the voltages available to modules being +12, +5 and -12 volts.

Choosing a PSU

There are plenty off the shelf solutions for power supplies, for example the tiptop audio μZeus which provides power through a brick outside of the enclosure and feeds it into a dedicated power module, you can also buy doepfer PCBs that do roughly the same thing without taking up module space. However luck would have it that MEAN WELL sells the RT-65B, which has exactly the outputs we need for less than 25 euros! It does require a little more DIY effort to get it setup properly for our case.

The first thing we need to solve is the lack of headers on the RT-65B for our pretty ribbon cables to plug into, so I made a little adapter board. Eurorack uses a 16 pin (2x8) connector to supply power to the modules and since I already know I won't be using modules that require the +5v or any of the other extras (Gate, CV) the schematic is dead simple:

I added only one header to the bus board, making it the smallest bus board in the world ¹, It'll do though because I'll be using a "flying bus" cable to supply all the modules with power.

Its always a good idea to test your creations barebones before moving on

Maths seems happy! So having sorted the power situation all that is left to do is actually design a case.

CAD & Design

For the 3D models I used Blender with the CAD Sketcher plugin, CAD Sketcher is still in active development so it has its rough edges but for small projects like these it's been a real joy to work with. It's got an active discord, some YouTube videos on how to get started and it is open source, what's not to like?

In this image each printed part is clearly marked with a unique color, the case is made up of segments each 22HP wide, which is: 111.76mm (1HP being 5.08mm, for details read the full specification on the the Doepfer website, the numbers aren't pretty ²) the walls and floor are seperate prints connected through 4 bolts and segments are connected to eachother using another 4 bolts, the rails connect to the walls using 2 bolts. I went a bit overboard with nuts & bolts required for connecting the parts but if there is any hill I am willing to die on its on hill "plastic snap fit connections are evil".

The rails is the only interesting part worth showing (we are printing a box after all), when assembled you slide square nuts inside the rails that way it's easier to mount your modules without having to worry about tolerances so much. But because of the shape of the rails it's best to print it standing up straight, it is such a narrow part however that you don't want to print it too tall or risk the print failing halfway. After experimenting a little I decided on 22HP being a good balance between print duration, aesthetics and module size needs.

Printing & assembly

Let's be honest, printing panels is a huge waste of time and plastic but it does make prototyping easy if you don't have a CNC machine or laser cutter. Two walls next to each other on my prusa mini take about 4.5 hours to print, the floor takes another 3 hours, a single rail – which I decided to print with 100% infill for sturdyness – takes about 2.5 hours, add to that the two sidepanels for 2 hours each and since I have about 84HP worth of modules I want to put in the case I literally needed to print for days. The final score amounts to:

(4.5 * 4) + (3 * 4) + (2.5 * 8) + (2 * 2) = 54 hours of printing.

Printing the rails was indeed the most risky since its such a narrow part printed vertically

In the end one out of nine rails printed failed on me:

Having all parts printed and ready, it is time to get out the nuts & bolts and connect all the parts.

About a quarter of an hour fiddling with a hex key later and voila:

What a beauty, and a final sanity check:

Maths is still happily doing analog computing, and here it is in action:

Conclusion

The box feels sturdier than I initially thought it would, probably a combination of factors: using nuts & bolts, gyroid infill, PETG and a heavy power supply inside the case³.

If you want to take a look at the design I have the blender project and the exported .stl files hosted on github over here, feel free to do with them whatever you want.