Monday, October 25, 2010

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.