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Thin back effect

 
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Mat Roop
Senior Member


Joined: 24 Mar 2007
Posts: 862
Location: Wyoming Ontario

PostPosted: Fri Oct 26, 2018 7:00 pm    Post subject: Thin back effect Reply with quote

I am working on a cheaper than cheap violin( no linings , rough bass bar etc etc.) that has significant sentimental value.
I'd like to make the best of it, but now that the back is off, and I can measure the thickness, it is generally not too bad in the bouts, but instead of the center of the back being 5mm thick it is just 2.8mm. The top is generally thicker than needed so that I can fix.

1-What would be the effect of the thin center back and ...
2-what might I do to compensate for it?

Thanks for your advice!... cheers, Mat
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Chet Bishop
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Joined: 23 Mar 2007
Posts: 657
Location: Forest Grove, Oregon

PostPosted: Mon Oct 29, 2018 11:33 am    Post subject: Reply with quote

I only have had to deal with a "too-thin" back once, but the following is how I did it (and, bear in mind that the instrument (a viola) was my own make, and I was compensating for having over-thinned the back):

I removed the top plate, and, using a slice of a large mailing tube (5" diameter, as I recall) cut to fit the curvature of the back plate, inside and out, cling-wrap of unknown brand, and a patching plaster commonly sold in hardware stores, I proceeded to make reasonably accurate casts of both the inside and outside of the back center area.

I selected a slice of matching maple, same species, at least, about 5 mm thick, cut it to an appropriate shape for the breast-patch, and soaked it in the water-bath of the glue-pot, while the casts continued to dry. (I was in Arizona at the time, so they dried fairly rapidly.)

When the casts were hard and the wood was hot and flexible, I clamped the patch into the inside center of the back, using both casts and as many clamps as it took (it turned out to be pretty easy to get the wet, hot maple to conform to the dry cold back.)

Finally, after the patch had dried into the shape of the back, I removed the clamps, slathered the inside of the back plate patch-area, and the bottom side of the patch with hot, strong hide-glue, and clamped it back in place.

When everything was dry and hard, I planed the patch down until the graduations matched the desired thicknesses, and called it good.

Reassembled the viola, and it turned out to be one of the best violas I ever made. Rich, deep, growly voice. I was very pleased with it, and so was everyone else.
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Chet Bishop
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Mat Roop
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Joined: 24 Mar 2007
Posts: 862
Location: Wyoming Ontario

PostPosted: Tue Nov 06, 2018 3:05 pm    Post subject: Reply with quote

Thanks Chet... that is a nice solution.... especially on a good instrument.
I'm just going to leave this one and see what happens... after all this is undoubtedly the cheapest of cheap vso's i have run across... so I am not expecting a lot.
Cheers... Mat
ps.. I was taken by the process of soaking the patch real well and clamping to fit.... makes me wonder why that is not done with the feet of bridges...ie... just do a reasonably close fit without being persnickety, and use the pressure of the strings as the clamping force. Should create the ultimate perfect fit. ... I'll be trying it on the next violin.
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Chet Bishop
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Joined: 23 Mar 2007
Posts: 657
Location: Forest Grove, Oregon

PostPosted: Mon Nov 12, 2018 10:15 am    Post subject: Reply with quote

"Been there" on that one, too!

I had a bridge that was nearly a perfect fit, but not quite...and I did not want to go any further with it.

So, with the strings tensioned, thus the bridge feet held very firmly against the varnished violin belly, and, holding the violin in a vertical position, I put a single drop of hot water on each foot, so that it had to soak into the place where I could see a tiny gap.

Within seconds, the water disappeared into the hairs-breadth gap, and soaked into the bridge-feet.

Within a few minutes, there WAS no gap, and upon drying, it never came back.

The bridge looked as if "it jest grew there!"
Smile
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