A drive on the back of a MacBook — from idea to product

This is how I make a product for a need of my own. This is a rewrite of the live “hdd-case” post from the full video. On your approval I replace the live post's text, keeping the hdd-case slug, as with the two earlier rewrites.

The problem

I use a MacBook, and like most MacBook users I keep an external drive, because the base model's built-in storage is small. The trouble is that the drive takes up desk space and looks untidy — especially on the move, or when I use the laptop without a desk.

The idea

Design a case for the drive, put magnets in it, and let it stick to the back of the MacBook. The first step was a rough design and the basic requirements: hold the drive, take magnets inside, and be easy to swap.

Test prints

To get the sizes right I didn't just measure; I printed test pieces. There is error all the way from measuring to the finished print: the measuring tool, the printer, and the shrinkage of the material. So I printed a small piece to test the width and the curved profile of the drive, and only from those did I know the true sizes to put into the design.

For the second and third requirements, magnets and easy swapping, I split the case in two and placed magnets around the edge, to hold the halves together and to grip the back of the MacBook. The two halves snap together firmly and don't fall apart. At that point I thought it was done.

Aluminium is not magnetic

But I had forgotten one thing: a laptop's back is aluminium, and aluminium is not magnetic. I looked for solutions online. Most people use a MagSafe ring — the inner ring — stuck to the back of the laptop, with a steel plate or the other ring on the drive, attached when needed. Which means a ring sits on the back of the MacBook permanently. And it is ugly.

While reading, I came across something else: Apple puts small magnets at the corners of the MacBook's display — to hold the lid shut, it seems, and to signal the system to sleep. So I went looking for where the magnets sit on my own machine.

They sit very close to the edge, on all four sides. The idea carried on: as before, I printed a prototype to test whether it would hold. It held.

It has to feel good, and look good

For me a good product doesn't just work; using it has to feel good, and it has to look good. On feel, I don't like opening and closing with magnets: I need magnets to stick to the laptop, not for opening and closing — that action has no satisfaction to it. I prefer a sliding mechanism, like the old slider phones, or some of today's cases. So I changed the design: still two parts, but they slide into each other. Far more comfortable to take apart and put together than the magnets, and it doesn't fall off.

The magnets that hold the case to the MacBook are hidden inside. And I gave it a face I like: I'm fond of Pokémon, so Snorlax.

And so I had a drive that does what I need, designed to my own taste.

Not quite all: the cable

In use, plugged into the MacBook, everything was fine. But once I unplugged it, the cable was still there, dangling, catching on things in my hand or in my bag. So I added a cable cradle on the drive itself, clipped the cable holder in, and that was that.

This is the final product. It doesn't just satisfy the function; it feels good to use, and it looks good.

A design tip

Design is trial and error, over and over, to find the best version. Through it I try to keep to a few rules: what to design first and what after; which dimensions to set first; how files and folders are named. That saves a lot of time when something has to change or be improved later.

For example: once Snorlax was finished, it took about five minutes to make another variant, Gengar, and then Blastoise.