As promised, someday is here, and I am finally getting around to posting a little about the work that goes into the instruments I build.
After selecting and cleaning a tin I think will make a good instrument (not too many dents or corrosion, a tight fitting lid, and good artwork) I always make a measured drawing to plan the instrument. Then I mark out the center, the axis of the neck, the bridge location, and several concentric circles on the tin bottom to guide shaping the steel.
I do all the hammering to shape the tin before starting work on the neck or any other parts. Shaping the tin is the most iffy part of the process, and if the work fails I don’t get stuck with a neck that was custom made to fit a bad tin. In the picture above you can see concentric circles marked in black ink. I have already hammered down the outermost ring using the ball end of my hammer to start the downward part of the curve, and the center bulge is starting to rise as I work out from the center.
This picture shows the curved top of the anvil I use to shape instrument bellies. Starting in the center of a tin, I stretch the steel by striking it between the flat side of the ball-peen hammer and the anvil head. As the steel stretches in the center it bulges up and I work out toward the edges little by little. It takes a countless number or hammer strikes. A heavier hammer or harder blows would make the work go faster, but I find that the result is less even and more likely to collapse when the string tension is applied to the belly of the instrument.
The resulting steel instrument body must have a very even and rigid dome shape to stand the pressure of the steel strings and be flexible enough at the outer edge to resonate with the plucked strings. The steel work-hardens and becomes more brittle as I hammer so there is a limit to how far I can stretch things. The bigger the tin the more hammer work is required and the more sensitive the dome is to small flaws.
Next time I’ll get into the nit-picky work of adjusting the belly of the tin for the off-center bridge foot print.