Fixing The Tuner Gears Of A Sony CRF-320

I’m a huge fan of Sony’s industrial design between 1970 up to around 2005. The coolest device in the category that I own is hands down a CRF-320, a radio receiver. It weighs in at 13 kg and covers 150-30000 kHz, that’s all of FM/AM/LW/SW. It’s a beast and it’s very collectible.

It’s also prone to have problems with the AM/FM tuner gears. The receiver was manufactured in 1978 and these gears are made out of nylon. Nylon tends to dry up with age and since the gears are mounted on a metal shaft they will shrink around it until the tension is too great and they crack.

I’ve been meaning to get metal gears to replace them but I’m too mechanically incompetent to even know where to look. There are a million different metrics of a gear (diametral pitch, backlash, pressure angle, etc) and me, a simple code boy, would prefer to just use my calipers under magnification and model a copy in AutoCAD. So that’s exactly what I did.

Now I’ve seen a 3D printed replacement gear you can order from Shapeways, a service where you can order a printed copy of someone’s model for a fortune. However, the gear the someone made was a super simple version of the actual gear and I wasn’t ready to shell out that much cash for two of them (and inevitably more for when I fuck up) so I did the only sensible thing and bought a 3D printer.

Now I don’t think there’s anything wrong with selling something you’ve made through Shapeways. I bet the guy spent a good five minutes on his gear and he should be fairly compensated for his work. However, I’m also a firm believer in building strong passionate communities with open source hardware and software and a great way to do that is to share what you make for free. I mean how many Sony CRF-320 owners are there out there? A few hundred? Dozens? Well, if you’re one of them shaking your head over Mr Burn’s five minute gear heist I’d love for you to download my much more accurate 3D model for the astronomically more reasonable price of zilch:

Download Sony CRF-320 Tuner Gear Here

I printed a few of them in PLA and I found that the best way to mount them on the shaft was to bore the hole until it fits snug on the shaft. To do this I used a drill as a tiny lathe while holding the gear with plyers, starting with a 5mm drill and moving up to a 5.5mm carefully. I don’t recommend going up to 6mm, instead putting even pressure on the inside while drilling.

Imagine doing this to a 12 EUR piece of plastic you had to wait for to get? Terrifying.

Finally, I used a small metal tube and the lightest hammer I have to carefully nudge the gear into place on the shaft.

Happy tuning!