Saturday 26 June 2021

A 3D Printed Project Case

Prevarication. Yep, for quite some time, I've been putting off getting into 3D-printing, but a recent thread on the VI-Control Forum got me thinking (which is always dangerous), and that led to me trying out a 'pathfinder' project. So here's what happened...

Never The Right Size

Boxes or cases are one of the hardest parts of building custom electronics. Commercial boxes or cases are never quite the right size, or they never have quite the look that you want... I have spent way too many hours looking for perfectly sized, good-looking 'professional' cases, then buying them and finding that dimensions are not always correct, plus appearance is very subjective, and as a result I have quite a lot of cases that turned out to be not quite the size or look that I wanted - plus mostly-finished projects that are still waiting for a decent case... You know the sort of thing...

Photo by Nicolas Thomas on Unsplash

I know that I'm not the only one, and when I saw a thread on the VI-Control Forum asking about how to mount 100mm sliders for a long-throw MIDI Controller (why are sliders always so short on MIDI Controllers?), then I read it with great interest. First, I found out that metal panels were not as difficult to fabricate as I had imagined, and then.I kind of volunteered to make some 3D designs and do some testing of commercial 3D printing companies. Well, it definitely got me doing something

As you might expect, there are a number of places that will do 3D printing for you (which is a good way to 'try before you buy', especially if you already have one hobby that is prone to Gear Acquisition Syndrome (GAS: synths!). I did a Google search in the UK for '3d printing on-demand one-off UK', and found several companies (you should localise the search terms for your location, of course!). 

The costs were not as high as I expected, some of the companies had quite sophisticated ways to estimate the costs of 3D printing a part, and overall, the capabilities varied enormously - you will need to acquire some knowledge in order to understand the materials used, the file formats used, how to prepare 3D files, and various other bits of jargon - but more Google searching will quickly fix that.. Four example notable companies that I found were: (Seem to be 'hobbyist' oriented...) (This is very 'Pro' in feel...) (£50 minimum order)

The learning curve is not that steep, really, and there are some free 3D drafting applications available to produce the STL, OBJ, AMF, or 3MF files that describe then3D object you want. I used TinkerCAD, a free web-based application, from AutoCAD, to produce the 2 STL files for printing a box and lid. Because I was expecting to get things wrong at least twice, I chose a very simple case - just something to house a switch and some jack sockets for a monitor switching box.. The STL files were for the box and the lid:

My first two STL files :for a box and a lid

I used to do the prototype. Their online quote generator took the STL files and showed me what the box and lid would look like (useful confirmation!) and how much they would cost, and generally made it very easy to place an order... The cost was about twice what a similar sized plastic or die-cast metal 'hobbyist' box would cost, except that this box was exactly the size I wanted, and could have any holes, legends or decoration on it that I wanted. I chose the 7-10 days economy service, ordered two sets of box and lid so that I was over the £40 minimum order value, and waited for the parcel to arrive.

The TinkerCAD web-app was pretty easy to use, with lots of tutorials available on the web-site. I would almost suggest that some music software has a bigger learning curve...So whilst I was waiting, I designed an angled box which is more like I would want for something to hold some sliders or a MIDI Controller...

There seemed to be some interest on the VI-Control Forum for a few designs as starting points for people wanting to make their own cases, so I will make all of my designs freely available on the TinkerCAD site. Here's a more develop version of the previous box...

This case reflects my own personal design preferences, but it wasn't that difficult to make, and there's a huge advantage to getting a case that is the right size, instead of a compromise. 

Here's the boxes and lids that arrived:

The texture is interesting: it is matt, and quite smooth, really, but those highlights make it look much rougher. - it certainly didn't have the obvious lines that you see on some home-printed 3D parts. One thing to note is that whilst this looks like it is full of carbon and conductive, it is just black nylon, and so it is an insulator. You would need to sort out screening if you had any high gain electronics inside - but if you make wooden cases then you face the same problem... 

So here are all the bits, plus a plan for the holes. I did a bit of guestimating based around the jack sockets and the switch, and didn't give myself very much room beyond that, so this is a much smaller case than I would normally get for this type of project. 

 Here's the drilled case, using one of those stepped pyramid drills that are perfect for making holes in thin metal. The black nylon is easy to drill, although because it has been 3D printed, it does tend to melt if you try too hard with the drill. The walls of the case are about 2nn thick, and it seemed very strong. 

I always buy stereo switched jack sockets, because you never know when you might want some clever functionality, and the cost difference in bulk is very low. In this case, I didn't need any switching or resistors around the jacks and I wasn't going to PCB-mount them, so bending the legs over was a good way to save space.

And here are the jack sockets, with all the legs bent to save space.

I've probably mentioned this before, but doing a test assembly as early as possible can be very useful. Here's me trying to figure out the optimal placement of the sockets...

Doing a test assembly also gets you a better feel for  how all the bits fit together in 3D!

In this case, I figured that arranging the sockets in two rows of three was best, and so I used double-sided tape to fasten them together. Using the case as a jig when soldering wires can be useful, but sometimes solid is better.

Here's the common 'Sleeve' grounding of the jacks. I'm ignoring the Ring connection , so these are all going to be mono jacks - my monitor speakers are all mono wired. 

And all the wiring completed. There's no gain in this box, and low impedances, so I have used screened cable for these very short wire runs.

And here is the assembly check using the box as a jig. Everything seems fine, so I turned the box over and moved the sockets and switch inside...

What I discovered is that I could probably have made the case even smaller...

The interesting thing about 3D printing is that the parts you get are exactly the size you specify in the 3D file. Unlike moulded plastic parts, there are no slopes so that the parts will fall out of the mould, and so I specified that lid to be slightly larger inside than the inside of the box, and so the two parts snapped together with a reassuringly tight fit. A little bit of glue would make it very strong indeed. A little bit more time in the 3D drafting package and I'm sure I cold have added a hole and receptacle for a bolt or two...

One thing that I did get wrong was the height of the jack sockets - I took the overall height, not the bit that would be inside the box, and so when you subtract the parts of the sockets that are outside the box, then you get a case that is too deep! I may try to cut it down as en exercise in making neat cuts. And don't forget that the sides of the box are parallel - you can cut it down and the lid will still fit perfectly. There are no hidden slopes or tapers here!

Completed! Yes, I should have put some text or symbols onto the outside of the box, but I'm still learning the 3D drafting software. But overall, for a first attempt, it isn't bad. Most importantly, I know that it isn't that hard to make a custom 3D printed case, and I've staved off the GAS need to buy a 3D printer for the moment. (Although there's a very well-equipped local MakerSpace that has 3D printers and laser cutters...)


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