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Tag Archives: crack repair

I’ve been a fan of Roland Chadwick’s music since hearing a performance of his trio for classical guitar, Letter from LA, a few years ago. So I was delighted when he contacted me about a guitar that needed some attention.

It was a fine instrument too – a cedar top classical guitar made by an Australian guitar maker, Simon Marty, in 1988. Quite apart from being 25 years old, it had worked hard for its living and the thin cedar top had developed some nasty cracks in the widest part of the lower bout. Some of the internal braces had come unglued too, and the guitar was more or less unplayable. To make matters worse, someone had tried to repair the cracks with superglue.

This is what it looked like after I had scraped away most of the superglue.

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With a hand through the soundhole, I could feel that the cracked part of the soundboard had become detached from a long transverse bar running across the instrument under the bridge. This explained the multiple little dowels, which were a previous attempt to fix the problem. The only thing to do was cut out the damaged wood and replace it.

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I also needed to replace some missing braces and re-glue several that were beginning to come unstuck. The difficulty here was that the braces, constructed out of balsa wood and carbon fibre, were very thin and it was almost impossible to position conventional clamps accurately enough to hold them in place without distortion. In the end, I solved the problem by making a few spring-loaded miniature go-bars. Wedged between the back of the guitar and the top of the brace, they kept everything in place while the glue cured.

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After re-polishing, it was ready to perform again. All well worth the trouble because, despite its age, it’s an excellent guitar which produces a big warm sound.

 

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My cello is making progress, even if rather slowly. I’ve just closed up the box, which is a step that requires a lot of clamps to hold everything in position while the glue sets.


And here’s the problem: where to find enough clamps. One solution is to buy or, cheaper, make spool clamps for the job. But these clamps are less than perfect because the force they exert operates at the edge of the plates rather than directly over the ribs. For clamps that put pressure in the right place, you have to buy a set of the dedicated cello clamps made by Herdim®, which, I’m told, are easy to use and work well. Unfortunately each of the Herdim® clamps costs about 15 Euros, so getting equipped with the 40 or so that are needed for a cello is quite expensive.

Partly out of meanness and partly because I enjoy making my own tools and jigs, I devised this alternative. The photographs make it fairly clear how the clamps are constructed and instructions are probably unnecessary. But perhaps a few details will be helpful. The clamping force is supplied by a wing-nut on 6mm studding. I made at least half of the clamping length out of aluminium tubing so that the clamps were as light as possible. It’s important that the aluminium tubing has an internal diameter only very slightly greater than the diameter of the studding so that the upper part of the clamp slides smoothly, but without play, over the lower part. The clamping pads are mahogany but, of course, any hardwood could be substituted. When making these pads, it’s a better idea to work a rebate into a length of cross grain mahogany and then saw it up than to craft each one individually. The pads are lined with cork that has been glued on in a profile that puts the pressure directly over the ribs. I used polyurethane glue to set the tubing into the clamping pads and to cement the studding into the aluminium tubing but I should think epoxy would work equally well.

The same principle also works for shorter clamps. The one below is designed for crack repairs. Shallow cleats are temporarily glued either side of the crack, which the jaws of this clamp can grip to close the gap.

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