Friday, November 21, 2008


After lots of research and speculation I have decided to try and repair a small gap that occurred in the first binding/purfling strip I added. Actually, it's two gaps, each about 0.5 wide, one between the binding and purfling and one around the rosewood veneer line between the purfling and the soundboard.

Had it only been a gap between the binding and purfling, the matter would have been much easier to resolve as I could just have filled the gap with sawdust and glue. But, it's the gap around the rosewood line that bothers me. If I was to fill that I would give a visual appearance of the line growing twice as thick for about 1" and slimming down again to it's normal size. Not good. The question next was how to to fix it.

I had numerous correspondences with fellow forum members as well as a telephone conversation. Several suggestions as how to fix the problem were mentioned. One was to just add some more glue and clamp the binding in. Another was to make some sort of space at the end of the binding, heat it all up to soften the glue, move the binding into place and reclamping it. Yet another, a variation of the second one, but also adding fresh glue before clamping it.

To figure out how Titebond glue would react to heat I ended up calling Franklin International's, the manufacturer of the Titebond glues, tech support to get the inside scoop. A very friendly tech person informed me that all the Titebond glues does indeed do work as hot melt glues and not only once as some had suggested, but repeatedly so. He recommended heating the glue to a temperature around 240-250º F for best results. I asked if it would be necessary to add more glue to which he responded that as long as there was glue in the joint in the first place adding extra glue shouldn't be needed.

I did two little muck ups to run experiments on. One was a 4" long replica of a side with lining and soundboard attached, including binding a purlings with gaps like on the real guitar. The only difference was that I it made from walnut/walnut/spruce rather than bubinga/mahogany/spruce and that it was straight. Otherwise it was dimensioned pretty accurately and it was glued together with the same glue. The other muck up was just some binding I had glued to a piece of bubinga. The idea was to start practicing on the latter just to get a feel for how much heat I need to supply to get the glue soft and then move on to the more elaborate one for a complete trial run.

During the process I tried to reclamp part of the binding just as it was and another part with extra glue added. For some reason I had better luck with getting the binding to stick when I added more glue. I don't know exactly why that was, but I speculated that it may have been because I didn't keep it clamped long enough for the glue to cool down and solidify. Or, maybe I didn't heat it up enough to properly melt and therefore not being able to adhere properly when it got clamped again. Who knows, but because of this I decided that it was probably best to move ahead with the job by trying to open the joint up a little and add more glue.

After some serious procrastination, I took the plunge and got on with it. I opted to drill two small
1/8" holes, one for the purfling and one at the binding centered around 6mm, 1/4", from the side of the neck. This allowed for 1mm for the neck still to have to come off in the final carving process, 1.5mm of slope in the heel from the top to the bottom of the binding, 1.5mm radius of the drill bit and still have at least a 2mm thick wall between the hole and the heel.

I carefully started drilling a shallow hole for the purfling, though it ended up a little deeper from the repeated attempts to get a decent photograph of the process, and a slightly deeper hole for the binding matching it's width. I used my caliper to measure the progress by sticking the depth measuring blade into the hole. I used a hand drill for this which worked really well for this
with it's slow operation; No unpleasant surprises of the bit suddenly digging in and coming through the neck.

Next came the softening of the glue. I was very nervous about this. Not that it would be difficult to heat up the glue for the binding, but because I was afraid of heating up the glue around the linings too, weakening the joint between the soundboard and sides.

With the tip of a household iron I began to heat up the binding, being as careful as possible to keep the iron on the binding only and not overheat the area in general. It's a good idea to empty the iron before doing this to prevent the water from the iron to spill all over. Don't ask me how I know this. With a drill bit inserted into the hole I gently tried to pry the binding away from the neck to create a small gap in the joint where I could squeeze in some more glue. But, that didn't do the trick. Instead of the binding on the body opening up, the little bit of binding left on the other side of the hole gave way.

Instead I resorted to just heating up binding
to soften the glue around the gap and reclamping the bugger in place.

I made as small semi circular cork lined caul out of MDF, that fitted the diameter of the soundhole. I used a flycutter for this. I don't really like using flycutters but the tool worked really well for this application, as the bevelled end of the cutter created a little lip that held the caul in place an prevented it from falling though the soundhole. I did a few dry runs before the real deal, to figure out which clamps to use and where to put them. I found that using three wooden cam clamps covered the troubled area pretty well.

Once that was sorted out, I reheated the binging again as before,
added a little bit of fresh glue on the gap and scraped as much glue as I could down into it with an old credit card and added the first clamp furthest away from the neck. This pushed the binding in place where the clamp was and opened up the gap a little more in front of it. This procedure was repeated for the second clamp, though the gap in front of the clamp did not seem to widen further when it went on.

The third clamp went on about less than 1" away from the neck and managed to close the last bit of the gap. I wasn't able to detect whether the end of the binding had moved further in to it's pocket in the neck or not, but speculated that it must have done just that and it only a very small forward movement was needed to press the binding in place. The three clamps were left in place overnight for the repair to dry.

Once the clamps were off, the binding was scraped flush with the sides and the clue was cleaned up on the top. On close inspection of the repair revealed that the binding was as good as new. I was still able to trace an approximately 0.2mm gap on one side of the rosewood veneer line but it was a lot less than before and not something I think anyone will notice unless you know it's there.

All in all I was quite pleased with the end result, particular in the light that this it was a task I dreaded doing and one that had been hanging over me for a some time.

Onto the fingerboard....









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