Friday, May 7, 2010

Making the mold


Before we start cutting on the violin wood we have to make a mold. The mold is the pattern the ribcage is built on. I print out the form I drew of the Titan violin back. It is drawn 3-4mm smaller than the finished violin plates. The ribs are about 1mm thick so that brings the 3-4mm down to 2-3mm. That is the overhang. Violins have a top block that holds the neck, a bottom block that holds the button, and corner blocks that make the ribs easier to glue in the corners. These are notched into the form. The end blocks I made for this one are longer than the others I have made. The original mold has cut outs for the blocks the same length top and bottom, and the Strad poster has a CAT scan of the Titan that shows the entire ribcage...with top and bottom blocks the same size. If it worked for Tony I'll give it a try.
The corner blocks are notched in with a little forethought. In order to cut the rough blocks into flowing corners that match you have to have some guide. Even using a paper tracing from your original drawing like Strad did, or printing out another copy from AutoCad and cutting it out like I do, it is still hard to line it up with the mold. A neat little trick is to make the cutout so it starts where the corner ends. You can take a straightedge and mark the blocks using those two points. I learned that on maestronet.com (thanks Michael Darnton) I also read somewhere on there that making the corner of the cutout for the corner blocks bigger than 90 degrees makes it easier to pry the finished ribcage off the mold. I did an exaggeration of that and found that if I take a line from the bottom (or top of the upper corners) of the blocks across to the other side it goes through the corner as well.
I saw the blocks out and get them ready to glue on. I have 3 spacers I place under the mold, on a flat table or board, so when the blocks are glued on, that side is pretty level. It also puts the mold in the middle of the ribs so there is space on both sides to glue the linings on. That side will be the back. The belly side may not be level, depending on the original rib heights. This one is almost straight. Bending a belly a few mm's here or there isn't a problem. Now that the mold is ready we need ribs.

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