Bridge Pin Height Regulation, was: More, More (wasRe:TharSheBlows!)

Richard Brekne Richard.Brekne@grieg.uib.no
Fri, 23 May 2003 15:42:24 +0200


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Farrell wrote:


In a bridge pin hole, two directions have end grain, and hence the
general concern.

Well, I suppose I could be convinced this creates a problem, but I'd
have to see more then whats been layed on the table so far.
 On a new bridge, I don't understand why you think it is advantageous to
drill a loose-fitting hole for the bridge pin, as opposed to a snug fit
- still swabbing the hole with epoxy on the snug fit.

I get the feeling here we are taking for granted a difference in pin fit
that probably is not so big. Loose pin fit doenst mean wobbley or
anything. Being able to just push a pin in with your fingers is not
exactly "loose fitting". I put the fit closer to the term snug then I
would loose fitting. Point being that swabbing the hole with the epoxy
either way yeilds very much the same result. The advantage I see is that
I find it easier to push the things in, it avoids completely the
potential miss on the drive angle which damages the hole, and I like the
extra little bit of knowing the pins are bottoming out in solid
material.
 Again, just bringing up some thoughts. Some folks do think that a pin
will bond into the hole when using epoxy. There have been posts in the
past about concerns regarding difficulty of removing bridge pins that
have been epoxied into their holes. In a refurbished bridge, I think
epoxy is essential to fill voids in a poor pin/hole fit and to fill the
eye-corner cracks so common next to bridge pins. On a new bridge I don't
know that it is necessary, but it certainly can't hurt anything, and can
only serve to fill any small void related to drilling imperfections (on
a tight fitting pin), and to strengthen the wood immediately next to the
pin as some epoxy will be absorbed into the wood fibers. It seems to me
that a standard tight pin/hole pin driven into an epoxy-wabbed hole
would be fully advantageous as it has the advantage of traditional
direct wood support, some frictional resistance to pin movement and the
benefits of epoxy, whereas a loose pin/hole fit would only rely on the
epoxy which does have some softness associated with it - its not a
brittle super-hard material.

Bringing up other thoughts... :)... even tho bonding is not a motivater
here, the fact that that is going on would seem to counter the concern
about too much being absorbed into the endgrain. And the (extremly)
slight degree of softness the epoxy has associated would seem to me to
be a plus, in as much as there is no way its going to be so soft to
cause any problems, and yet it may help the wood avoid being crushed
when the hole shrinks due to climate changes.... certainly cant hurt.
Also, I dont really see that any up/down movement of the pin is an issue
either way. The side bearing alone should be enough to keep that from
happening unless the hole gets reaaaallyy loose.

And please, this is discussion - lets discuss apparent or potential
advantages/disadvantages - as I am only trying to seek out what appears
to be the best method to install a bridge pin.

Gee Terry,  I thought thats what we were doing.  :)  Seems to me some of
these same points I've mentioned have been echoed by several others as
well. Is there something going on I havent picked up on yet ?
  Terry Farrell
 Cheers
RicB

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html


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