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This set of photos shows the
doubling of the edges now complete and my solution to the problem of
numerous cracks and arching distortion under the bass bar. Unseen in
the photo with the heat lamp is the plywood counterform lined with
vinyl that I made, which is under the area being pressed out with
heat. This worked very well, almost fully returning the sunken
arching under the lower end of the bass bar area to it's original
shape. After pressing it out a couple more old cracks opened up.
This was a good thing because I was able to reglue them before
fitting the reinforcement. As you can see, I have added a cross
grain reinforcement under the full length of the bass bar except
where the breast patch is. This reinforcement has a final thickness
varying from slightly under 1mm to nearly nothing at the edges and
near the breast patch, but it reinforces all of the cracks in that
area and supports the corrected arching. Also, this reinforcement
reduces the sudden change of structural stiffness at the edges of
the bass bar. Engineers call this a stress riser and it is a major
cause of cracks. Another advantage of doing it this way is that
after trimming, the reinforcement provides a clean, regular and fair
surface for accurately fitting the new bass bar. With these things
done, the trickiest (and scariest!) part of the repair is now done
and for the first time in many years, the top has a clear ringing
tap tone which only occurs when all of the cracks are well glued and
reinforcement are secure. |
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