Bass tuners counterboring

[Marco Pancaldi]

I noted in the Mike Lull basses a good idea to keep good string angle before the nut when using modern tuners with bolt nut instead of grommets. It makes a conterbore (probably a couple mm depth) to set the tuner lower.
I want to make the same on a modern Fender American, but i need to start from a 17 mm hole, to counterboring the headstock face to 24 mm...the problem is to keep well centered the big forstner bit in the smaller hole. Have you some advice? I hope to not plug it and redrill from scratch...

Thanks
m.

[Paleo Pete]

I can only take an educated guess, but I would think the best way to go would be either milling machine or drill press. Trying to do it by hand will almost certainly let any tool you use "walk", and there is a possibility it will also dig in and cut a lot deeper than you really want. This is something I don't think I would try myself, without some good machinery to do it with. Drill press and a padded vise would probably work ok, and if I were doing it I'd probably try either a bottom cutting end mill or router bit. Some sort of stop would also be a good idea so it doesn't cut too deep.

[jbltwin1]

Best answer is to use a shadow board that is clamped to the headpiece. Clamp the shadow board to the headstock and drill through it into the headpiece. It will allow you to keep the headpiece centered. Or if that makes you nervous, drill through the shadow board ahead of time with the same sized forstner. THEN clamp it to the headstock and use it for the centering guide. Mike.

[Bruce Johnson]

Actually, the simplest and safest way to cut those counterbores is to use a counterbore cutter. They are actually quite easy to make up in custom sizes if you have access to a metal lathe and a milling machine. Do you know a local machine shop? I've made up a lot of custom counterbores for other Luthiers, including that size for that exact purpose. I have one that I made up many years back, that I use just for recessing the bushings of that style bass tuners. It's used in a drill press, with no special fixturing. The pilot on the end centers itself in the existing 9/16" hole, and the teeth are shaped to gently cut the counterbore without pulling up the surface. The design is actually very simple. I machine them out of O-1 tool steel rod stock.

If you want me to make one for you, it's about $40. Look up Johnson's Extremely Strange Musical Instrument Co. in Burbank, CA