DIY 5 position magneto start switch, or 6-12 position, whatever!

**Damo78** · 11-22-2015, 03:01 PM

Hi all
Well, trying to find a 5 position key switch for a low budget cessna build is pretty hard. I did find one, from a certain US website for around $120 which I thought was a 'little' steep for a key on a computer board.
So… off to maplins (UK overpriced electronics store) to buy a tumbler lock and key. Bushpilotwannabe popped me onto the idea of using a rotary switch instead of an actual 5 position diesel key i had, which I've done, and here's how.

So, here is the lock, taken apart, which means unscrewing the one screw at the back. The key item (pun very much intended) is the circled piece in pic below.

This has a ridge in it that catches the barrel and stops the key tuning further.

This currently allows 3 clicks/positions on a 12 position rotary switch I had. Some rough workings out showed that the angle between the 2 notches on the washer were 120 degrees, so 40 degrees a switch position. So I filed away to 200 degrees, the blue line on the pic above.

Now attaching the rotary to the key. Well, seeing as there was already a screw hole in the back of the key i thought I'd try and cut some threads onto the rotary. It ended up being 4mm.

Although not a 'machine screw thread' in the key, it created its own thread and now fits snug as a bug.

So, now the key turns the rotary switch. I've filed the washer to stop the revolution at 5 positions, but remove the washer and you could have all the switches of your rotary. Just clamp the key casing and the rotary base and let the key turn.

Cost... £3.49 for the key, £1.49 for the rotary. Tools already had, and if no tap and die then you could cut to a tip and cement into the key.

Now I've a good excuse to make a panel and add some switches.

Thanks for reading all. Was pleased it worked!

Damo