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reglueing long top crack, double bass

Giovanni Corazzol

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"...never such a sight... cleats don't fail me now!"


Please help me in planning this double bass repair. The 3 ft long top crack over the soundpost has reopened - and the cleats placed on the many rib cracks are very unstable.

Some questions about these repairs and tools i will need.

Is it correct to start with freeing the soundpost crack and reglueing it in sections, from the center first?It is well aligned at least.

I have thought to use small metal "toolmaker's" clamps with spruce studs and plastic wedges.

I have seen the "calamari" clamps in other threads; this is my question: they look easier to make, do they work better also? I'm not sure if I will find a suitable plastic pipe to make them. I have ordered some aluminum bars to make the other kind of clamp.

I have seen the clamps made of wood and brass screws, (O. Kishony) but I fear to glue clamps directly to the plate, in this case; I think that it would save time but I don't feel experienced for using this method. cleaning the old crack will be difficult and i want to clamp the crack sides securely and immediately before the wood dries. Just another question about wooden pillar clamps: their glueing surface is endwood, do they hold without putting much glue?

Some long-reach clamps will be needed for cleating, I will use some of the aluminum bars to make cleating clamps about 12" deep. Section will be mm 25x6.

The lower bout rib will probably need the elimination of all the cleats (they do not hold, crack sides move, they add a lot of mass) and doubling with veneer; I have read about using a 3-layer, thin and flexible "plywood" that is produced for model making. Is this correct?


Thanks in advance for your attention comments and suggestions!








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 Just another question about wooden pillar clamps: their glueing surface is endwood, do they hold without putting much glue?

Some long-reach clamps will be needed for cleating,




If you are referring to the "traditional" wooden pillar, they are fit like cleats (not end grain).  I recommend you check out this article: http://hudelmayer.com/about-me/articles/hold-on-tight-the-strad-nov-2001-article-on-crack-repair/ it is a well written article and explains the mechanics of pillars and wedges.  It is a wonderful system of aligning and gluing cracks, however, it is not always necessary to use them.  Often a simple strap clamp will suffice. Sometimes something more complex is needed (specialty jigs, etc.)




Is it correct to start with freeing the soundpost crack and reglueing it in sections, from the center first?


Working from the center out is usually a good way to go.  That way you are moving from an area of lesser flexibility (plate movement) to an area of greater flexibility, making the job of alignment easier .  Doing it in sections is probably a good idea. 







Some long-reach clamps will be needed for cleating, 



There was a thread recently concerning the use of rare earth magnets for clamping.  I've used them for a few years now when installing cleats.  Less cumbersome than dealing with long reach clamps.


Good Luck!


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I'll start by saying that I'm a violin/viola/cello luthier, and don't really know bass repair. Just a couple of thing to add to this:


Do basses require soundpost patches the same as the other instruments?


I've used the thin plywood (1/32" Birch) that you're talking about. It's pretty good stuff. You'll need to make counterforms of some type, as any thin wood will warp when the glue is applied.


For the pillar clamps, I made some up using 10-24 J bolts, brass knurled nuts, and delrin for the moving block. The delrin is about 1/2" thick, and is easy to machine with regular tools, like a bandsaw and drill press.

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Jerry Lynn, FiddleDoug: thank you!


I knew the "hold on tight" article already, but I only had a black and white photocopy (some parts of the text were missing also...). I have studied it again!


The strap clamps are handy, but... the article shows that the farther the clamping points from the crack sides, the harder is to align and keep the correct shape of the arching. In double basses with long ugly cracks in tops or backs I think there's no better way to go than with "pillars and wedges". I feel that I will need strap clamps frequently anyway, so I will make some in my workshop. In general, few companies have good strap clamps in their catalogues now. I am especially nervous with the "double rail" style, full of unnecessary knobs, and so expensive. Mine will be more similar to the ones pictured in the Weisshaar book.


I have some 7075 aluminum (ergal) and threaded rod now, I will try to make some small parallel clamps to use with pillars and wedges in bass repairs. Something similar to clamp "A" in the article could be fine but, I would like to simplify it and make it lighter. I cannot make a XL size of clamp "C" (I have some and used several times) so I may try the regular size with "horseshoe"-shaped studs.


After 6-7 years I have made much bass setup and ordinary repairs for students, orchestra/jazz professionals and I know that basses have the crudest repairs. I rarely see quality instruments here and I almost never meet any musician who's able to spend money on them, all jobs have to be made fast and good enough. Sometimes an anonymous, battered instrument that plays remarkably well finds a more generous owner. Another thing I can say,  it's that bassists frequently have a warm, friendly attitude as customers as well as musicians; with no exception today, the better among them must find their career outside Sicily and, not rarely, outside Italy.


Thank you again for your help, I will post some pictures of the tools and the work in progress.





May 23, 1992



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