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Hi all. Here goes. About a year ago_, I saw an auction for a Bellafina Musicale 4/4 cello with spruce top and maple sides and back (all plywood) that was a music store return because of a sound post "poke through." For several months, I watched as the price was lowered in an increasingly drastic spiral. And I kept wondering, how difficult could this repair be? I finally purchased it. Upon arrival, I noted that all of the assessories were ebony (except the tailpiece, which looks to be a Wittner type composite with integral fine tuners) and the finish was well done.
The hole cleanly pierced the inner layer of spruce and the outer layer splintered leaving one end of the wood (for the most part) still attached. In theory, I should be able to fit a glued maple patch through the f hole (kind of like building a boat in a bottle) with a small round spruce plug already attached to fit the missing inner layer of plywood. When this is in place (secure by circular magnets) and while the glue is still wet, I should be able to glue the outer plywood splinters back in place.
A photo of the area in need of repair is attached for examination.
The following is a progress photo on the Cello repair. I cut a 1-3/4 inch by 3-3/4 inch piece of 2-ply maple veneer (Sauers & Company Veneers, 3 sheets of 8.5" x 11" that I got from Woodcraft for $16). I cut a radius on the ends to dress them up.
I used a digital 6 inch indicator to measure the thickness of the top plate of the cello at the f holes, and divided the thickness in half to estimate the thickness of the bottom layer of plywood. It would have been easy to cut off a length of cello sound post for the patch, but that would mean that I would have to glue to the end grain. That is not good. So I cut square blocks from a piece of spruce 2" x 4", cut them on a hobby chop saw to the required thickness, and chieseled the pieces to create circles. I glued one in the center of the maple veneer patch.
I was going to use magnets to hold the patch in place during the glue up, but I did not think that I could get an effective clamping force by the use of that method. I am going to use 6 segments of cello sound posts for clamps (I am going to use 2 sets of magnets for patch alignment). I have a cello sound post insertion tool (see photo) but the seller did not offer a sound post length gauge for the cello. I made one by cutting down the expanding steel handle for a small shop mirror (cost about $3). I glued 5 mm ball bearings on the ends so I could use a sound post magnetic slope indicator (obtained from the same place I got the sound post insertion tool for about $5). I drilled a segment of a spruce cello sound post and glued it to the sound post length gauge so that it would fit into the sound post insertion tool.
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