The Graduations

Well, it's graduation time again. I'll be carving the insides of the violin plates and I'll need a few guides so that I don't go too far. First of all, I don't want to remove any wood from the edges, where I'll need to glue the plates on to the ribs. I went through all that trouble flattening them, and I want to keep them flat. I use a compass to mark an even distance from the edges, a distance of 4.5mm, if I remember correctly. Then I "bridge" the dips in the corners to allow surface for gluing the the blocks, and draw straight lines across the bottom and top, 18mm from the scribed line on the plates, to allow for the neck and end blocks. Whatever else happens, I don't want to go past these lines.

But how do I keep from cutting too deep and tearing through my plates?
This handy contraption serves as a depth guide. It's just a dowel glued into a board, with a rounded, leather-padded tip. This simple jig is arranged so that, by setting the depth stop on the drill press and setting the plate so that its face touches the padded dowel, I can drill a guide hole into the plate, without fear of going too deep.

It's not quite so easy as it sounds, because the depth stop has an inaccurate gauge, and I have different depths that I have to drill to in different ares of the plates. Consequently, I have to set and reset the depth stop, drill into a test piece, measure that, and perhaps reset the depth stop again. Then I drill all the holes that require that depth, and repeat the process. When that's all done, I go in with a gouge and carve away until I get to the bottoms of the holes.

I use a "cradle" to support the arch, and to keep the plates from rocking back and forth, as they would clearly do if I attempted to carve their insides without one. Once I get down to the bottoms of the holes with my gouge (a time-consuming process) I switch to fingerplanes. This concludes the rough graduation.

Now I have to come back to this whole thing, drill more holes, and repeat the process. But before the final graduations can be done on the top, the f-holes require a little TLC. First, they need "fluting." Fluting the f-holes is a process by which the lower lobes are scooped out so that they don't stick up, get caught on things, and break off. Fluting also has an acoustical effect on the final instrument, since it changes the resonant frequencies of these lower arches.

This isn't a very good picture, but you'll get the idea. Next I finalize the arches of the plates, then I'm ready to cut out the f-holes. In order to get a good idea of when to stop once I've gotten through the second set of drill markers, I flex the back and top (gently), then I decide whether it feels right to me. If there are any areas stiffer than others, they need to be treated; if the whole plate is still what I would deem to be too stiff, the whole plate must me thinned.









I will not be blogging the f-holes or bass bar on my next post. They will have to wait for two posts from now. Something different has come up and, at the request of the customer, it will appear in my blog as well. But it's probably perhaps a little more interesting.