Crystal Radio--Air Variable Capacitors (4K)

We'll review the parts and "how to's" of variable capacitors and go over some unusual ones.

[@marvinwiseman3449]

4 bank capacitor for an AM / FM radio. The fewer plate sections are for the FM.

[@adnacraigo6590]

Small mechanical marvels when you think about it.

[@tsbrownie]

It's only recently that I've begun to appreciate that. I've always taken them for granted.

[@MrKarlGP]

I think the slower tuning one might have a planetary gear within the white plastic section... much sought after especially for the fine tuning requirements of the very narrow amateur shortwave bands :)

[@tsbrownie]

In these, I 3d printed the knobs. They're just plain plastic no mechanism.

[@MrKarlGP]

@@tsbrownieDIY knobs, excellent! :)
I have repurposed screw caps from bottles as knobs before, using a little Milliput (epoxy modelling clay) inside the cap to accommodate the spindle and a little drill hole in the side for a securing screw :)
Perhaps bearings around the rota are responsible for the slow tuning in the tuning capacitor you featured?
Vernier tuning dials tend to be horribly expensive.

[@tsbrownie]

@MrKarlGP My son's 3d printer has made things I only dreamed of before, possible. In the past I'd drill 2 holes in a piece of plastic and carve out the space in between. It was slow and inaccurate. I have no guess how that 2 speed dial works, and don't know what it is called, so I can't look it up.

[@franzliszt3195]

I'm going to try milliput. There is no way I can do 3d printing!@@MrKarlGP

[@graemezimmer604]

The ball Bearings at the front work as planetary gears to link the two shafts together. So simple.
Plus those Banks are actually called "Gangs".