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I've seen one or two passing mentions of using bottle caps for volume/tone knobs, but no details. It's not that difficult, so maybe everyone else figures it out just like I did.
But in case you want a head start, here are the specifics:
Materials: a 3/4" wood dowel, a bottle cap, glues (silicone or ceramic, and epoxy)
Dimensions: cut a piece of dowel 3/8" long. Drill a 7/32" hole in the center, all the way through. If possible, use a power saw to keep the sawed surfaces parallel and square to the sides and use a drill press with a vise to get the hole parallel to the dowel. This will make the knob fit straight on the pot shaft and turn concentric with the shaft (no wobbling).
Assembly: glue the dowel to the inside of the bottle cap with silicone caulk, ceramics glue (e.g. Duco) or whatever. With modern bottle caps, there is a plastic seal inside; the dowel will fit just inside the sealing ring, and the glue will only hold it against very light force. The only thing the glue does is hold the dowel in place and keep the epoxy from seeping into the center hole. Mix up about a teaspoon or two of epoxy and push it onto the gap between cap and dowel with a toothpick or coffee stirrer, making sure it's more or less evenly distributed all around. Let it harden overnight.
A 7/32" hole is slightly smaller than a 1/4" pot shaft, so you'll have to carefully squeeze it onto the shaft the first time. The metal of the shaft should press grooves on the inside of the wood, which will make it go on and off easier the next time, but still provide a snug fit with no slippage.
There you go - awesome knobs for about ten cents in wood and epoxy.
Metric users: 3/4" ~ 19mm, 3/8" ~ 9.5mm, 7/32" ~5.5mm, 1/4" = 6.35mm, 1 tsp = 5cc.
You know those drill bits that are designed to cut 1" holes? I use them to cut sound holes and the like, and when I'm done drilling the hole I end up with a circular piece of wood that I have to manually remove from the drill bit. Once removed, the circular piece of wood has with a hole in the middle which might be usable for the shaft of a potentiometer. So, I'm thinking maybe I should save them and use them to make wooden knobs. You may have to experiment with different sized drill bits to see which ones fit the potentiometer shaft, etc. And then you could glue a bottle cap onto the wooden knob to add some character or color to your CBG build.
You can use the core slugs from a hole saw for the wood donuts. I have used some vinyl automotive vacuum port caps designed for 1/4" line. Pushed them into a 5/16 nut and potted them into the bottle cap with epoxy. the vinyl presses over the shaft of the pot and works well.
Phrygian: For me, it was easier to cut off the slabs of dowel and then chuck them into the lathe for center drilling. But I realize few of us have lathes. Finding the center is no big task - there are inexpensive tools that do this that. Then you punch a starting pip with a center punch or a nail, and the bit will find the center. But, honestly, we're talking about CBGs here, so personally I wouldn't be too bent out of shape if the knob was a millimeter out of round. I know some strive for PRS standards, though.
Rand and Thomas: Using a hole saw slug is a great idea! Only possible issue there would be that the grain runs across the hole, rather than parallel to it as a dowel's would, so the shaft might split the wood before it presses the knurls into it. I hope you'll give it a try and let us know how it worked.
Right! I didn't consider the direction of the grain. I guess I should use plywood, then the grain won't make much difference. Well, this project isn't very high on my project list just yet. Need to find a local source for potentiometers. Now what's the Chinese phrase for "500K Ohm Potentiometer", not to mention "tone pot with a linear taper" verses "a volume pot with a logarithmic taper". Communication with the locals here is often a big hurdle for me, so maybe I'll wait till I'm in the States again next summer.
Plywood sounds like an excellent idea.
Last month I rebuilt an early '70s Epiphone MIJ (Tokai) Casino hollowbody. One of the problems was that the wiring harness insulation was crumbling inside the braided shielding and everything was shorting out.
I bought a new Epiphone branded harness - pots, switch, jack - for under $20 (incl. shipping) on eBay from a Hong Kong supplier. I'm now considering whether to rewire the '70s pots for CBGs, or just buy another Chinese harness and split it apart.
Anyway, they now make the Epiphone electronics in China, so if you can figure out how to ask, you can probably get one for a couple of bucks.
The direction of the grain depends on the piece of wood you use. Just cut slices from scraps with the grain in the direction you desire.