Two and a half years ago, I found myself sitting in a car with Eben Upton about three days into my new job at Raspberry Pi. We discussed – among other things – everything we wanted to do with the Raspberry Pi hardware and with the products around the Pi.
One of the things we discussed was an official Raspberry Pi case. We thought that it would be great to create something affordable, but with the kind of real beauty and design that our products try to encompass.
So to this end we began the search for a design company who were capable of understanding our requirements and had their eyes firmly fixated on creating a product that achieved those aims.
Kinneir Dufort (click that link; there’s a lovely demonstration of how the case comes together) came to our attention and turned up with an amazing first set of ideas. Of all of these Eben and I were completely bowled over by the one on the inside front cover of the report (which contained in total 6 main designs and 20 secondary designs). But to make sure we weren’t being driven in the wrong direction we decided to continue with three main designs, which came out of prototyping looking like this:
Kinneir Dufort went away and created 3D designs and models to understand how they might work (or not work) and returned with the following:
During the meeting we wanted to reduce it down to a final choice but found it really difficult to get there. Eben decided to make some small changes to the lovingly 3D printed version:
We liked the idea of them adding an area for the logo but there wasn’t enough room, so Eben made room!
Next, Kinneir Dufort refined this to create a more complete model of the three designs with input from Eben and me. We finally decided that the Construct design was the ‘right one’ and they proceeded to finalise the design to be suitable for injection moulding.
We spent months refining the design until we got to a point where we thought that Construct – the case we’re selling today – was as good as a case possibly could be.
Meanwhile we went looking for a partner to work with for the manufacture of the cases and the design of the injection moulding tool. (And this, for those of you – I know there are some – who’ve been watching this project avidly since we first mentioned it and have been struck by how long it’s taken us, is where the delays came in.)
Initially we worked with a company based in the north of England to create an injection moulding tool. During this process we learnt a lot about injection moulding!
Injection moulding is quite simple in theory. You build a metal tool to shape the plastic. You take some pellets of your base material and mix in some master batch (that’s the colour pellets which you mix in around 1 – 2 percent). You then put these into an Archimedes screw that turns and pushes the pellets through a temperature-controlled system, which simultaneously melts and mixes the plastic.
The picture above is of the injection ram. Once the plastic is melted and pushed into the ram the ram then presses (with around a double decker bus’s force) the plastic into the mould.
Now, due to the massive pressures involved here, you simultaneously need to press with another double decker bus from the opposite direction to stop the plastic just spraying out of the mould. The next step is known as packing (this is ‘just keep pushing’ because as the plastic cools it contracts, making slight imperfections in the finish). From the picture above, you can see pipes at the top of the metal tool. These are where a coolant (usually just water) is piped through the mould to help cool the plastic, otherwise it gets deformed when you open the tool up.
After about 20-30 seconds of cooling (during which time the Archimedes screw is heating up the next shot of plastic) the mould is opened up and the plastic is ‘ejected’ from the mould by all those pins!
You can see the ejection pins pushing the plastic out of the mould. If you get this wrong, the ejection pins will just make holes in the plastic!
In practice there are some things that maybe you might not have thought about. The time it takes to cool down is related to the volume of plastic injected and the thickest parts of the mould. This limits the speed at which you can make the cases, although you can flush through more cold water to help cool it, but this has a knock-on effect because you now need to push the plastic into the mould quicker, or you end up with lumpy bits of partly hardened plastic!
Also, you have to be careful pushing plastic from a thinner area to a thicker area because it doesn’t spread very well (meaning you have to push it for longer). Plus all of this stuff has to be done using very, very hard steel (remember those double decker busses…) which you can’t work on in normal ways like using drills, a file and a bit of elbow grease. Instead you have to use magic electrolysis (like they taught you at school), The picture below shows the copper anodes used to create the tool for various parts.
We spent a lot of time asking the toolmakers to make changes and the moulding company to press out some new cases – and then being annoyed that they weren’t perfect. We went through literally dozens of imperfect iterations – lumps here and there, clips that didn’t clip, inconsistent colours, ill-fitting parts, bits dropping off the case, incongruously fragile and snappy corners – and eventually we gave up and moved our business to a company a little more used to the type of high quality injection moulding that we required.
T-Zero, the company we should have gone with in the first place, is based in Dudley and employs a small team of dedicated people who know all this stuff upside down and back to front. They’re brilliant. Plus, they know a toolmaker, who doesn’t just know what he’s doing, but is also capable of turning the air blue whilst he’s doing it. :)
We met Brendan, Simon and Mandy because we really needed a second opinion about the tool we had already paid a significant amount of money for and that didn’t seem to be any closer to being finished after a year of small improvements. They looked at the tool and agreed that it could be salvaged and that they would be able to create the case of our dreams!
They then spent a couple of months working with us and their toolmaker to produce some truly awesome finished cases. The pictures you see above were taken during this process. The final case now clips together cleanly and stays clipped together, all the interfaces are ‘just right’ the colouring is perfect and it can be made in the quantities we were hoping for. We’re really proud of it.
So in conclusion, it’s not just plastic. It’s about design, love, attention to detail, accuracy, iteration and overall damn hard work! We think you’ll love this new case as much as we do. It’s functional, it’s very good looking, and you can pick one up from our own Swag Store, element14, or RS Electronics. (If you’re outside the UK, their local representatives – MCM Electronics, Newark and Allied in the USA and some other locations – also have them available; and we expect to see the cases appearing in other partners’ stores soon.)
If you’d like to know a little more about the whole process then please ask away in the comments.