Stupid Luthier Trick #4

[JLT]

Back again with a device that I had to invent for gluing those little square shims onto a soundboard.

I was given a Martin guitar to repair from a musical therapy group. it had two problems. First, the jack in the tailpiece had come unthreaded and was practically falling out of the guitar. That was an easy fix. But a harder one was a crack in the soundboard on the edge of the lower bout. I took it to my mentor Arnie Gamble and discussed the repair with him. I had already decided to run glue into the crack and clamp it not only downward on the soundboard but by closing it using a clamp across the lower bout. He told me that the repair wouldn't be complete without gluing small diamond-shaped shims to the crack from the inside...the same shim we usually use to reinforce the soundboard seam. So I added that to the repair.

Easier said than done, I found. The closing and gluing of the crack was routine, but after the crack was glued back together, I couldn't find a way to hold the shim in place on the inside of the guitar. So I devised this clamp:

guitar shim clamp 2.jpg

It might show the detail a little better by showing it at an angle. The shim is attached to the clamp's end using a weak double-side tape

Guitar shim clamp 3.jpg

This third picture shows the clamp in use. I loosened the strings and used a shock cord to hold them to keep the sound hole accessible.

guitar shim clamp 1.jpg

I removed the top of the clamp, leaving the bolt in place. Laying the bottom bar onto the guitar, I ascertained exactly where it should be located to put the shim where it should be, marking where the edge of the sound hole would be and the angle it formed from the center-line of the guitar. Then I applied some fish glue to the shim and fed the bottom part of the clamp into the guitar and into the precise location. When the shim made contact with the soundboard, I moved back and forth slightly to get a little adhesion going.Holding the clamp bar in place, I put the upper part of the clamp onto the bold, threaded on a wing-nut, and tightened it until the clamp was applying steady pressure onto the shim.

What you're seeing is really the top bar of the clamp, rotated about 80* to the bottom bar of the clamp. You can see the bottom bar inside the body of the guitar, applying pressure to the shim located just a little and to the side of the bridge.

[mike243]

Nice! You said, " I had already decided to run glue into the crack and clamp it not only downward on the soundboard but by closing it using a clamp across the lower bout." I don't see the clamp for that. Did you run the glue in the crack, clamp it on top and bottom of the soundboard, and then add the shim (cleat) and apply pressure only from the bottom with the tool you made?

Thanks,

[JLT]

Nice! You said, " I had already decided to run glue into the crack and clamp it not only downward on the soundboard but by closing it using a clamp across the lower bout." I don't see the clamp for that. Did you run the glue in the crack, clamp it on top and bottom of the soundboard, and then add the shim (cleat) and apply pressure only from the bottom with the tool you made?

That's right, more or less. I first closed and glued the gap between the soundboard and the rib (there was no binding there) using a cam clamp to squeeze the gap shut. After that, I glued and closed the crack itself by using a bar clamp across the soundboard at the lower bout. The next day, after all the gaps had been taken care of and the glue had dried, I glued two diamond shims to the soundboard on the inside using my gadget.

I didn't take pictures of the first repair steps, only the last one with the gadget in use.

[Kevin Sjostrand]

That's a pretty smart stupid trick if I've ever seen one.

[tippie53]

creative
No true discovery was ever made by status quo thinking

[Stray Feathers]

Synchronicity is a lovely thing . . . I have been mulling how to close a crack on the back of a tenor ukulele I made and gave to one of my stepdaughters. During a move, it was left in the car overnight in Jasper in winter, and when the car heater was turned on in the morning, I guess it did not handle the sudden change in temperature. Anyway, I have heard lots about various ways to close cracks, but in the case of a uke the soundhole is too small to get into to place magnets or guitar string/tuner type "clamps". Your elegant clamp looks like it just might work! Bruce W.

[mike243]

Thanks for the additional information!