Klarinet Archive - Posting 000049.txt from 1994/08

From: Clark W Fobes <reedman@-----.COM>
Subj: crack repair
Date: Fri, 12 Aug 1994 01:35:02 -0400

A recent post here touted the efficacy of cyanoacrylate ester (super glue)
as a means of repairing cracks in clarinets.

I have used "super glue" mixed with grenadilla chips as a filler after
pinning cracks. I have note that in many cases that even when a crack is
well pinned, the super glue can work out of the crack. This is probably
due to the constant moisture/temperature fluctuation and attendant expansion
and contraction of the surface.

There is , however, a distinct disadvantage to this method. If the glue
(or any filler) is applied before the crack is allowed to close, the
introduced material acts like a permanent wedge further aggravating the
existing stress.

I usually pin about 0ne to 2 dozen clarinets per year which means
installing approximately 3 dozen pins. I have developed a method over the
past ten years that has proven very effective. In only 2 cases over the
past ten years have I had a problem with a crack re-appearing in the
affected area.

I believe that it is important to use the "through" pin method rather
than the "blind" pin. In the first method a pilot hole is drilled completely
through the clarinet from surface to surface. (Between the bore and the outer
surface, of course!) A blind pin uses only one hole, that of entry. I
have seen more of these open up over time than the "through" pin method.
I am certain that wood dust builds up in front of the pin as it is run
into the hole. If this material has no place to go (an exit hole)
additional stress is created forcing the crack to open wider.

With clarinets I do not think it is necessary to set the pins diagonally
to the line of the crack. I believe this method was developed primarily
for oboes which have much smaller outer diameters. Running the pin at a
diagonal allows for a longer pin, more holding surface, and more room for
error. I make my holes 18mm from entry to exit with the crack bisecting
the line of the pin at the center. I space the pins at .75" intervals.

The main advantage to drilling holes perpendicular to the crack is that
the operation can be done on a drill press. I was taught by a craftsman,
Bob Flemming of Fresno, CA. He would chuck up a drill in a bench motor
and run the thing through by hand! I did it this way a few times and just
never felt comfortable. I have yet to ruin a clarinet by drilling into
the bore. May my record remain perfect!

If a crack runs through a tone hole I fill the crack in the tone hole
after the clarinet has been pinned. I do not like to replace the tone
hole, because it is possible to engage an entirely new set of problems if
the glue around the insert loses integrity over time.

I suppose this topic has taken my attention because I am pinning two
clarinets this week. These things seem to come in rashes.

Clark W Fobes

   
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