Bending Sides

Time to bend some sides. For this instrument I selected some Honduran Rosewood I've had seasoning for quite some time. It's pretty hard, and it has an almost glass-like tone when I knock on it. I've planed and scraped the sides down to slightly more than 2mm (.085"thick). I'm comfortable bending things by hand using my electric iron, but it's much faster to use this bending fixture I made. The form is glued up from MDF board and the pattern has been reduced in size to account for the thickness of the sides and a silicone heating blanket.




At one time I had the more traditional "Fox bender" setup where the sides were sandwiched between metal sheets and a veneer screw put pressure on the waist. It was heated with 150watt light bulbs. I was never really happy with the results it produced.
My current bending system just relies on some gentle pressure from my hand on a block of wood. It takes less than two minutes to get things clamped in place using the threaded rod and knobs. I dampen the side slightly with a sponge and clamp it fast at the bottom, then apply pressure, moving forward to the waist. The heating blanket is draped lightly over the upper bout and it slides down into the curve with no problem at all! When all is in place, I turn off the heat for about ten minutes to cool down, then turn it on again for a further five minutes. This seems to set the bend a little better.

Here's my steel-string mold, with an attachment I screw in place for the cutaway. The side is clamped in while still hot, and it seems to relax into shape. I use springy maple slats (reject lute ribs) to hold the sides in place, sometimes with the help of F-clamps. There's a nice snug fit.

Some bracing work.

It's time to brace up a steel-string top. I rely on the tried-and true X-bracing system. Here, I've glued the supporting members above the soundhole. I don't play around here - these are large in dimension and made from the stiffest spruce I have in my stockpile. So much of the guitar's longterm stability relys on the support system that carries the fingerboard and transfers force to the sides of the instrument. My x-brace however, tends to be a little lighter than the typical factory instrument. When coupled with adequate design, this will increase the output and sustain. A delicate balance is required. I pay very careful attention to the interlocking lap joint which occurs at the intersection of the X. This has to be perfect.

I shape the X brace by paring away at it a little at a time. I use auditory information to help arrive at the proper dimensions. Before doing this work, I'll put on a pair of hearing protective headphones for an hour. All extraneous noise is eliminated from the shop. I want to be attuned to the task, my sense of hearing at it's optimum. I excite the soundboard with this little mallet I made from a superball and a stick. It gives me a more uniform and repeatable tone than my knuckle. I don't tune the top to a particular note - what I'm looking for is a certain clarity and complexity to the tone when I tap in various areas. This is augmented by using my thumb and forefinger to gauge the flexibility of the top. At a certain point, I'll get the impression that the top is flexible enough to provide good projection (without being floppy), and will have arrived at it's optimum response sensitivity. This is different for every guitar.

Following the shaping of the main braces, I'll glue on the secondary bars. This is all done in a special shaped carrier I made for my go-bar deck. I don't use a spherical dome, as is so often the case. The spherical design is an excellent aid to speeding production, but I prefer to graduate the degree of arch in the soundboard from nearly flat at the fingerboard end to a gradual arch of about 1.5mm in the center of the lower bout. I see no benefit to the severe doming employed by some luthiers. Some degree of arch is necessary of course, to alleviate of the tendency of the soundboard to crack in dry weather. The arch also counteracts some of the deformation caused by string pressure. The scalloping in the main braces below the soundhole allows a greater degree of sensitivity. I definitely strive to make the top much more flexible as it approaches the area of the sides. This produces a larger active vibrating area, which in turn gives us more volume.

Staking his claim

This little creature has been visiting every day for the last week to check on progress. He/She has definitely picked out a favorite instrument for napping on. Puns abound. Perhaps it wants to play "Cat Scratch Fever", "Cat's in the Cradle", or simply holler, "Go Cat, Go!" before tearing off into a wicked four bar rockabilly solo. Dunno. But one look in the eyes, and you know you'd better keep your hands off that guitar.