Thanks Dan, the soak and heat process was in my mind. Did you notice any advantages to the curved back other than looks?
Yes they are pretty, but I couldn't distinguish any tonal quality changes. The center of the jig is "proud" of the frame, when you tighten the bolts it bends the panel into place. Wetting the panel in hot water in the bathtub, then using a hot air gun whilst torturing the panel in the jig. Hope this helps, always fun to experiment!
Thanks Dan, the soak and heat process was in my mind. Did you notice any advantages to the curved back other than looks?
I did a few Virginia pieces years ago, there didn't seem to be any interest in them then. I wet the panel and placed it in a clamping jig drawing it to shape with the help of a heat gun. I let them dry for a few days and it worked quite well. Mike Slone and Kevin Messenger were gifted the pieces in Hindman that year.
Though he hasn't built any in some time, Jim Good made some carved dulcimers which would have a curved back. There are clips of him in the dvd The West Virginia Hills - A Tribute to the Dulcimer from Augusta Heritage Center (at Davis & Elkins College) working on one of them (I think)-- been awhile since I've watched.
I have experimented with the side to side curve, trying anything from no curve to 1/2 inch. Getting the back to curve more than 1/4" almost always causes the back to crack. A technique that helps with this is to bend the back when the wood is raw and apply a penetrating finish. This seems to fix the bend in place.
Instead of a curved back, I angle the sides making the tail 1/2" deeper than the head.
There are two curved backs of course which can be utilized separately or together. Curve from fore to aft; and curve from side to side. Each by itself is easy enough to incorporate into a design. I've seen dulcimers with 1/8" rise from side to side or head to tail. Several builders incorporate one of these two techniques to help direct the sound upward (to what degree this is successful I don't believe anyone has subjectively proven).
A 'bowl back' is hard to accomplish unless the builder starts with a thicker plank and "carves" the bowl shape into what will become the inside of the instrument. This is done the same way a violin top is carved -- with chisels, rasps and sanding. I don't know anyone who does this for backs-- it is certainly time consuming -- but Ken Bloom does it for the soundboards on his bowed dulcimers, but not, I think on the back.
I have noticed several builders are making their dulcimers with a curved back. Of course bracing would be needed but when you speak of the curve, how much deflection are you working toward? I can see where the curve should reflect a little more sound to the top and if the top were isolated from the fretboard you might get a little more volume.
Any thoughts would be appreciated
Bill R
