Building the Ole Bull Rib Structure

Building the rib structure for my Ole Bull was a bit different than the rib structure for my prior violin. This is due to two things: (1) the fact that the ribs are being made independent of the plates (usually the outline of the plates is determined based on the outline of the ribs - here, the two are separate); and (2) the ribs are not perpendicular -- because he top and back plates are different sizes, the ribs must shift and twist to accommodate and fit both plates properly.

To accomplish this, I am using a three dimensional form for the ribs, which consists of the usual wooden form with an acrylic plastic form on each side. The plastic forms accurately represent the rib outline of each plate, and the wooden form in between tilts accordingly and is of a thickness that allows the entire form to be the final height of the rib structure.

First, the blocks are installed and four templates are used to mark the blocks and corners. Then, the c-bout sides of the corner blocks are trimmed to the mark, leaving additional curvature to be trimmed off later. Because the blocks are not perpendicular to the table, it takes some time and patience to get the gluing surfaces for the ribs flat. Once done, the c-bout ribs are bend and glued into place, being careful that they make full contact with the plastic form on each side:

When the glue has dried, the remainder of the blocks are trimmed in the same manner, the edges of the c-bout ribs where they will meet the upper and lower ribs are feathered, and the upper and lower ribs are bent and installed, again being careful that they make full contact with both the upper and lower plastic templates (a few more clamps than one would usually use may be beneficial here):

With the ribs installed, the plastic templates are removed, leaving only the wood template and ribs. Mortises are then cut into the blocks, linings are installed flush with the wooden form, glued and clamped - note that due to the twist in the ribs, the linings require some additional trimming to ensure that they make full contact with both the rib and the form:

When the glue has dried, the clamps are removed, the corners are trimmed, and the ribs and blocks are trimmed to the proper height and taper:

Now, the only things left to do are to finalize the corners, cleanup the surface a bit, and remove the ribs from the wooden form.

Here is a photo of the back (which has now been hollowed and graduated) with the ribs and a photo of the back on top of the ribs (although I guess you really can't see the ribs in this photo):