starting to beat a tin into shape
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.
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.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.
And now for some time lapse!
5 hours of work in 1 minute 15 seconds from The Tinkers Damn on Vimeo.
completing the belly of the tin
pop! from The Tinkers Damn on Vimeo.
The video above demonstrates what I am looking to correct in this finicky part of the process. By carefully feeling around the belly surface (fingers are more sensitive to this than eyes) I can find slightly flattish spots that are weak and will pop (as heard in the video) functioning as a two position or bistable spring. These spots are trouble. I find they will have their own distinct natural frequency adding too much can noise (bark, rattle, and buzz) to the completed instrument. I do my best to eliminate these spots. In addition, I need to reinforce the area around the dimples to resist the string pressure on the bridge. Ideally the whole center of the tin belly will be rigid enough to vibrate with the string frequency while most of the flexing will occur in the concave curve around the edge of the tin.
Last episode, I finished shaping the tin. For part three of how it’s made I’ll give some details of cutting and shaping the maple neck and its extension through the tin. This won’t include the fret board. That will have to wait for another episode. Even without the fret board this may be a bit long, so hold on to yer hats’n glasses! After the initial work on the band saw, table saw, and drill press this is all hand work with rasps, chisels, and sand paper. Apologies for the sharp focus on the backgrounds. One day I’ll learn to force a digital camera to focus where I want it.
Now to get my head straight. This work will help set limits on the curve of the center part of the neck too.
OK, last part of this post, I swear.
raking light from my faithful swivel lamp, I look carefully for the edges of those facets, and eliminate them one by one with many grades of sand paper. Blue lines in the inset image highlight the edges of several facets visible in the photo. All these have gotta go. In addition, if you look close at the inset (you can click on the image for a closer look) there are two green arrows indicating that my “don’t cut anymore” lines are indeed still there.
In the last episode of how it’s made, I finished shaping a maple neck. Now it’s time to fit that neck to the cookie tin.
padauk), and the tin with its shaped belly. Note the long tail end of the neck. This will fit all the way through the tin body and will support the string anchor at the butt end. The neck angle relative to the tin body has already been set by the angle of the maple shoulder where the neck will meet the tin.
carpenter’s square I will extend that fading horizontal sharpie line down the side of the tin.
Norm, I ALWAYS wear eye protection. If you don’t have yours on right now while just reading about forcing a box cutter through sheet metal you should put on a pair of goggles without further fuss. Ahem… In the image above, I have cut through the T shape at the top of the opening. I will continue cutting (or can opening) along the red dots.
duck bill pliers.
That’s all for now. Next time I’ll get into trimming the butt end of the neck and getting the shoulder to fit snug to the tin. Buon metallo.