Crack Repair Using Tuning Machines - Luthier Tips du Jour Mailbag
In this episode, luthier and instructor Robbie O’Brien shows how to keep parts aligned with glue using tuning machines.
Video Transcription
[on-screen text reads: Luthier Tips du Jour Mailbag]
Mailbag question: How do you maintain alignment while gluing a seperated center seam on the back of a guitar?
Robert O'Brien: Today's Tips du Jour Mailbag question comes to us from Ireland. "Robert, I have to glue a back that has separated at the center seam. I'm worried about the pieces staying aligned while gluing. Can you offer any advice?" Steven, in Ireland.
Steven, that is a problem. When you're gluing two pieces together on the back, you want to maintain that alignment, like you said, of the two pieces. There's a really, really neat way of doing that. Now, somebody showed me this years and years ago. I don't remember who it was. It's a really neat trick of things just laying around your shop that you can use to help keep that alignment as you're gluing. Let's go over to the bench and I'll show you.
The problem
So here's the guitar that came in. Beautiful bird's eye maple and the center seam has separated. This is due to lack of humidity. It was quite a bit wider, had opened up quite a bit.
So what I did is first of all just humidify the guitar and get the gap to close. Now I've got the problem of gluing it back together and I've got this unevenness here. If I glue it back together and it's uneven on the two back halves, then that's going to cause a problem. So the center reinforcement strip is still glued on the inside, but there's a gap in there. And when I glue it back together, I want to make sure that that stays even. So here's what I'm going to do.
Drill some small holes
I'm going to start by drilling a couple of very small holes in this dark wood here. This is Indian rosewood. I'm going to drill a couple of very small holes in there. Dark wood is easier to hide things and patch things than in lighter colored woods.
[Robert uses a really small hand drill to drill 2 small holes down the center reinforcement strip]
Now the reason why I drilled those holes requires a little bit of explanation. I've made a couple of jigs here. Now I saw this somewhere years and years ago. I don't remember where I saw it. I'd like to give credit where credit's due, but I have no idea who came up with this. So if you know who this is, please tell me. I'd like to give them credit. This is just a little device that's got a tuner on it and you wrap a thin guitar string. Usually the high E, into that. You put that into the hole, and on the inside you wrap a small little block or something. You put your glue in here. This is on the inside. You have a guitar string here that you then wind and that pulls that up tight. And the pressure of this going down, the pressure of that coming up maintains everything in line. So that's what we're going to do here.
Attaching the string
Once I fish the string out from the inside, then I just place one of these little blocks on here that I've made, drill a little hole in it, and then just tie a knot in the string here. You could also wrap it around a washer or nut or something. Usually a couple of half inches around here on the end of the string is enough, depending on how big a hole you drilled in your block. And I wrap it around the tuning machine and wind it. And that sucks up in there tight and maintains the evenness or the levelness of the two pieces I'm trying to glue back together.
Winding the string
And the reason why I drilled two holes is because the separation here is pretty long. So I'm just going to put two of these on there to guarantee a little better result. From the top side, and I'll take my little jig, run this up to the center hole there and into the tuner. And now I'm ready to begin winding. And just wind it up in there until it gets tight. The pressure here and the pressure on the clamp on the inside maintains everything aligned. Very, very slick little trick there. Now I have to do is take this thing apart, apply glue, and glue it back up and life's good. So Steven, all the way over there in Ireland, thank you very much for your question and happy building.
[on-screen text reads: More Luthier Tips and online courses available at www.obrienguitars.com. Private and small group guitar building and finishing instruction available.]
