I have access to cable-TV. In a suburban block of flats, this is a bad thing, because that means one has access to only one Internet service provider, because the tenant-owners’ association, as a whole, will be too cheap or ignorant to connect to the free-market fibre grid in addition to cable. Which in turn, of course, means having to pay several times the nominal rate for decent broadband.

Another drawback with cable-broadband – besides being forced to have it, I mean – is the cable modem. Those things grow hot. On a summer’s day, they practically glow. And, worse, they crash and reboot. Constantly.

To be fair, the problem might be averted if you place the modem somewhere cool and airy. But, let’s face it, that’s often not an option. One has one cable outlet, maybe two with a bit of luck, and then a tiny coaxial cable. And if you’ve ever had to wrangle a coaxial cable, you don’t need me to tell you how unbelievably stiff and awkward they are, so even if you buy a longer one and get all the specs right, there is no way you will be able to wrestle that beast into submission and have it go exactly where you want it to go.

Even with a proper airflow, however, they tend to grow rather hot due to inadequate chassis design. So, I decided to do something about it.

Now, I have three pieces of network equipment. The piece closest to the provider is a Netgear CG3100 cable modem. As I have yet to come across a cable modem which isn’t garbage, it is configured as a network bridge, which is geek-speak for “leave everything the hell alone, just pass it forward”. Even these simple orders make it searing-hot at times.

That to which the cable modem passes everything is my second piece, which is my combined firewall and server. It is by far the most capable of the bunch, but unfortunately irrelevant to this blog post.

From my firewall/server, a second network cable connects to my third piece, a Netgear WNDR3700 wireless router. Flashed with custom firmware, this piece handles pretty much everything I throw at it, without getting much more than lukewarm.

The two Netgear boxes (boxen?) have to co-exist on a somewhat small shelf in a closed cupboard. Almost on top of each other. No wonder things get heated; but I have had the cable modem by itself out in the open air, too, and it still gets really warm, so I maintain that it suffers from thermal problems. But I digress.

My first idea was to mount a fan on top of the exhaust holes. However, given the extraordinarily poor airflow in the case to begin with, I doubt that would have done much. My second idea … was a bit more invasive.

Luckily, none of the devices appear to have warranty stickers on them – although warranty stickers are based on a shaky legal fiction to begin with, so it is debatable whether or not that would have stopped me anyway – and both were easily dismantled by removing a handful each of #9 Torx screws.

As can be seen, the printed circuit boards have the same general shape and outline, and probably start off looking the same in the factory. More importantly, the mounting holes are of the same size and have the same position.

Lacking the bits and bobs necessary to complete the project, and the gumption to slough off to the hardware store to buy them, I decided to do a prototype out of bamboo skewers, cotton cooking twine, and rubber bands.

It worked.

The crashes stopped, and the drop in temperature was almost palpable, so I deemed the design itself a complete success, if a bit lacking in execution. Onwards to the next step, then.

It works, it sort-of looks nice, it keeps the temperature down, and the construction is stable. Yeah. That’ll do for now. In the future, I’ll perhaps make a proper chassis and add a silent fan, as well as connect the 12V rails together so I can free up a wall socket.