A Collapsable Mold

When building a violin or viola, we make a simple wooden inside mold that the blocks are glued on to, and the ribs are bent around.  The linings can even be glued on, and then the blocks are broken loose, and the completed ribcage can be wrestled off the form like taking  a bicycle tire off the rim.

Archtop sides are only half the height of cello sides, but they are twice what violin or viola sides are.  I found that a 2 X 10 works perfectly.  It gives enough space to glue the linings on each side, so that when the ribcage is taken out it doesn't go completely out of whack.

But there is a problem on this one.  It has a cutaway.  I've found while roughing the plates that a cutaway will give a different sound than a full form guitar.  The size of the big mass is cut down.  You might think of it as a fancier speaker with a woofer, a midrange and a tweeter; instead of just a single multipurpose cone speaker.  It seems like you could get brilliancy, and good bass response, with thinner, more responsive plates.  At least that's what I hoping.

But it creates a problem.  Not for most makers.  Most guitar makers use an outside mold.  It just seems like a lot of work, a lot of wood, and that it would take up a lot of space. Besides, I'm used to an inside mold. But the dilemma is: how do you pry it off with that cutaway?

A collapsable mold.

Many violin makers make them.  I have one in the works for a Guadagnini violin.  For this guitar I made one up by taking 1 1/2" out of the center, and replacing it with a removable centerpiece.  The two sides are connected to it with 4 dowels, and 2 carriage bolts.  The blocks are glued to the ends, and I solved the problem of finding shims to add under the mold when gluing the blocks on by bolting two strips of wood of the correct height on the bottom side.  When I glue the ribs on, I can put 1 mm shims under them, and there will be stock on each side to plane off.

It should work.  Maybe not with the back glued on, but we'll see.

You can see the curly grain in this piece of wood I bought at Menards.  Fir I'm guessing.  It looked nice.  Isn't curly wood the best?

This is the completed mold.  Its final design was by mistake, but is looks like it was planned.  The dowels are slip fit; maybe a thou clearance, but one fell out, and is MIA.

The difference between a guitar mold an a viola mold.  The viola mold isn't completed yet.  It was cut down from another mold that I'm not using.

I found that my big Craftsman jointer works great on these ribs.