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I just installed a set of Gotoh open back tuners on a build I am finishing up.
The head veneer and backstrap ar gaboon ebony.

Of course I pre-drilled the holes for the screws. I waxed the screws as well.I also used proper size counterbore drill (stew mac) for the grommets on the top side.
I got some very fine cracking coming from the screw holes and between the grommets. not just in the lacquer (nitro) but in the ebony.

It's only cosmetic.,, but it sucks

Other then the obvious-Any Ideas? It has happened to me before, but not as bad. I have been doing this stuff for 40 years and its always something-this just really irritates me!

I wicked in some water thin cyano and when it dries hard I will sand and buff it out.

I just realized that both pieces of ebony are quartersawn, I think between ebony being so brittle and it being quarrtersawn that is a recipe for it splitting.

Dang, nothing worse than running into a problem right when you think you're done

Perhaps due to ebony being so hard as well? Maybe it needs just a couple thousandths more than other woods on the pre-drilling/reaming.

Another possibility is that the ebony is already under stress, so it cracks more easily. Its moisture expansion rate is so high, the water from the glue would expand it out a lot. Then after drying, it tries to shrink, but it can't. I've actually worried a bit about that, since I also put water on the outside of the headplate to equalize expansion and prevent it from curling away from the surface while I get it clamped. That's a lot of expansion during glue-up, which translates to a lot of stress trying to curl up the headstock or crack the headplate after it dries.

I've never actually used press-fit bushings before, but I will be on my current batch. All rosewood headplates though, and I'll be using a tapered reamer rather than the straight StewMac tools, so the pressure will be on the headstock wood further down the hole rather than the headplate.

And such a thin veneer. Same thing happened to me a few weeks ago, fortunately it was satin, so a quick fix.

Two things:

1) Use the largest drill bit you can but where the screws will still grab. Do your tests in scrap mahogany. I am currently using a 5/64" drill bit for Gotoh 510 screws and my Alessi and Rodgers tuners.

2) Very important!!! Use a conical bur to bevel the screw holes. This helps immensely when using backplates and also prevents the finish from chipping/flaking. BTW, these also work far better than countersinks for beveling bridge pin holes.

http://www.amazon.com/gp/product/B0006Q ... detailpage

Yeah, that is so frustrating.....I use a 2 drill bits, the first goes the required depth and just allows the threads to bite, the second is slightly larger than the threads/base of the screw and it only goes the depth of the headstock veneer, this typically prevents chipping..... Toonces advice is good.

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Gwaltney Guitars

Only done 4 or 5 open backs and never had an issue. I think in the future I will size the holes with CA. Maybe before finishing. Thanks for bringing it up.

Thanks Simon. Never beveled them before but I have seen a couple holes crack the finish. 5/64th bit also. The only thing I use my old timey hand crank drill for.

Cheers and best of the Season!

Thanks, Guys. All good suggestions. I forgot about beveling the hole for the bushing.
I do use a two stage hole for the screws.

If you look wrong at a piece of quartered ebony that thin it can crack.