Sunday, April 13, 2014

The HEAT is on!

My guitar sides in water

Hot! Hot! Hot!

Bruce Produces Lots of Heat for the sides of my new guitar. 

There are a lot of ways to bend wood, many of them so risky that a project might indeed break up right in front of you if you are not careful. Bruce Roper from the Old Town School of Folk Music's Different Stummer (he does their repairs) is building a guitar for me out of a highly figured set of sapele wood. Today is side bending day, which is more fun than it sounds and a little risky, too when you have such a beautiful set of sides to prepare.

First, wood bends, of course, but not this much. What you see up there are the sides of my guitar resting in about an inch of water. This has two consequences. 1. You can really see how lovely the grain is going to be on the sides of this guitar, and 2. They become  a lot more malleable after they have absorbed some water. I don't know why but it is a magical transformation. These sides are going to have to take on a shape they never imagined when they were part of a tree growing in west Africa. Bruce is going to help them do that.

Guitar building form
That guitar shaped thing resting on the work bench is actually a two-part, fiberboard form Bruce made in the shape of a 1938 Nick Lucas Gibson Guitar. What he has to do is take the sides he has resting in the water and make them conform to the inside of this shape. It's all done by meticulous measurement and gentle bending, with not much guess work involved at all. The two pieces of wood sticking up on the top and bottom of the form are the end plate, a simple piece of pine, and the neck block, which has a trench cut into it that perfectly fits an extrusion on the bottom of the guitar neck. Bruce's guitar necks are bolted on in a couple of different directions. That means you can get the neck off in a few minutes, but it remains stable and solid. He devised his system (others use similar systems) after decades of repairing guitars, particularly old valuable ones with necks that were glued into a dovetail. It can be hard to fix the neck on a guitar like that.

 The end piece and the neck block must be glued to the sides once they are bent and put into the form. They are important for a lot of reasons. One is strength. The glues Bruce uses are steam and water soluble, but very strong once they dry. So those blocks will play a central role (literally) in holding the guitar body in its shape and creating the opening for the neck. This is the point at which the project really starts to look like a guitar. So here is Bruce starting the bend. He is using an iron form heated by a propane torch. The wet wood will bend, with a little pressure from Bruce, around the contours of that hot form.

Bending a side
It's all a little more particular than it seems when you just see it in a picture. The sides are flat on the bottom and sloped on the top and ultimately will be planed to the proper dimensions. But first you have to get them in the forms. Bruce bends them in a couple of stages, starting at the top and bending down to what is called the bout (the waist) on the guitar. This is a process that involves feeling when the wood is ready to bend, Bruce says. You can't go faster or you might break it. He is practiced at this and for both sides, it goes smoothly. Bruce says sometimes, although not very often, a side will break during this process. Because my guitar is flitch matched (everything is book matched all around) breaking a side now would mean having to find a whole new matched set. As the tops and the sides of this one come from the same piece of wood and are quite distinctive, that would not be easy. Ultimately, these sides are going to carry a line of kerfing. Kerfing is a piece of triangular wood cut into a long strip with slits in it so that it can bend. One side gets glued to the inside top and inside bottom of the guitar, providing a little platform for gluing on the top and bottom.

But that's getting a bit ahead of the game. Bruce patiently bends sides and tries them into the form. Then he gets to a point at which he decides he has done enough bending, that clamps will do the rest of the work. He turns off the propane torch and puts it outside to cool. He dismantles the bending iron and takes it outside to cool, too. It's not a tiny shop, but it is a small enough shop that you don't want any blistering hot objects sitting around where you might put your hand on them.

He puts the sides in the form and marks and trims them so the forms will fit together.

Bruce uses a Japanese pull saw for trim
This is not as crucial a stage as it might seem. The end block and the neck block do a lot of the work where the guitar sides come together at top and bottom. Each will get a good layer of glue and will be clamped to hold the sides in the right places. The plate of the guitar neck will cover the one opening so no one will ever see it (unless it is a person removing the neck.) The heel plate will help create a gap that will be cleverly filled by Bruce with another piece of something. Could be wood. The important thing is that this little guitar bottom insert will finish off the bottom of the instrument and provide a handsome spot for drilling the hole that will hold the base peg (where the strap hooks in, if you are a strap wearer. I am not.)

It takes perhaps a dozen clamps to hold this all together while the glue dries. Bruce uses three clamps each on top and bottom blocks to hold them in place while the glue dries. While he is careful about this, he works confidently.

This wood has bent without crack or strain and dried nicely as soon as it was in the form. It will stay there for perhaps another 24 hours, when Bruce will remove the clamps and put in a set of spaces that will stay in place while he moves on to the next phase in the process, installing the kerfing and planing the sides to exact height to receive the top. The bottom is already flat and ready for kerfing and gluing.

Just a little more work is required on the braces on the top of the guitar before it will be ready for glue. You can see how the completed bracing looks. Where there is pressure on top of the guitar, there is bracing beneath to hold it all together.

But Bruce doesn't want to leave the bracing this thick as he is putting the top on the guitar. He will use his chisels to sculp the bracing make it as thin as he can. It must retain its strength without adding weight to the guitar. It might not sound like much of a trim, but bracing is one of the key components in how the guitar vibrates and makes its sound. That plate in the middle is a piece of maple. The bridge will be glued right above it on the face of the top, then the holes for the strings will be drilled through the bridge and through this plate. String it up and you have something that functions as one piece, strings and all, with the bridge plate transferring vibrations of the strings to the top of the guitar.

I'm pretty pumped about all of this. It's actually starting to look the way it will look when it is completed. The figuring in the wood is pronounced, and that will make it lovely. Of course, the big test comes when it's time to play, and we have a way go to before we reach that point. Stay in touch with us and watch us get there.

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