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wilsaxo

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Posts: 163
Reply with quote  #1 
A little over a year ago I was asked to do some work on a Hemen sarod's bridge to correct some string heights. I brought some files, abrasive papers, and jeweler's saw-blades to the patient only to find that the Jawari Nut was split under the opposing tensions of the playing strings on the one side of the instrument's neck and the Jawari strings on the other. My first thought that the nut needed replacement, but my second immediate thought was: could this be repaired using carbon fiber banding? The answer (at least as of this writing) was: yes!

Here are some before photos:
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010004.jpg
(oops! have to do some editing and remember how to post photos here,but until then...)
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010001.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010002.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010001-1.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010002-1.jpg
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wilsaxo

Registered:
Posts: 163
Reply with quote  #2 
Continued:
I ordered a jawari nut from the good people at the Ali Akbar College Store and, while waiting for it to arrive, commenced with the carbon fiber experiment. Since the bone was still intact at the bottom I felt confident that the banding would hold the crack closed firmly enough under the tensions it would have to handle in use. First I squeezed the crack closed and applied Super Glue to it. This was only to hold the pieces together while I was wrapping it with the carbon fiber so that I could do it as tightly as I possibly could. There is no glue strong enough to hold a crack like this together under the tensions involved with the tuned strings. Since this was the first test and I wanted to test it quickly, I used hide glue to soak the fibers with instead of epoxy. This allowed me to use bare hands instead of gloves. The glue, after all, is just to hold the carbon fibers together while the wrapping of the fibers is what gives the repair its strength.

http://i240.photobucket.com/albums/ff144/wilsaxo/IMG_3150.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010002-3.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010002-2.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010001-2.jpg

When the glue had set I installed it and re-strung the instrument. I tuned the Sa to a low tuning for this instrument: A=440 and let it sit for a few hours. It held the tuning, so I tuned to Bb, waited again, tuned to B and waited. After a couple of days I brought it up to C. The repair remained intact and the tuning stable, so I removed the jawari nut and applied a second wrapping of carbon fibers, with hide glue, for added insurance and did the final assembly. The repair is still holding over a year later.

http://i240.photobucket.com/albums/ff144/wilsaxo/P1010003-1.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010001-4.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010001-4.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010004-1.jpg
http://i240.photobucket.com/albums/ff144/wilsaxo/P1010001-3.jpg

David
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