Bridge Pin Height Regulation, was: More, More (was Re:TharShe Blows!)

[Richard Brekne]

Terry Farrell wrote

> >Arrrggggg! I have done that same technique on an old bridge as part of
> >refurbishing the bridge. I'd be afraid to do that on a new bridge. I
> >suspect there is always some resonable concern regarding how much epoxy is
> >absorbed into the wood and out of the void between pin and wood before the
> >epoxy hardens. My plan is to swab the hole with unthickened West System
> >epoxy and drive the pin into a normal tight hole.
> >
> >Terry Farrell
> >

Why would a (very) little epoxy absorbing into the wood be a problem ?


> Ron Nossaman wrote:

> I suppose it depends on what you think you want. If you think you want the
> pin bottomed in the hole, you can't use epoxy unless you arrange an escape
> route for the excess that will prevent the pin from bottoming - or blowing
> out somewhere else from hydraulic pressure as you drive it to full depth.
> That's going to be either an oversize hole, or drive it dry. If you think
> it isn't necessary for the pin to bottom in the hole, the epoxy can escape
> into the excess depth of the hole without making the hole oversize or
> blowing out elsewhere, or you can drive it dry. the one thing you can't do
> with an oversize hole is drive it dry, bottomed or not, and expect it to be
> functional.

This is all true enough as far as it goes. I do use essentially oversized holes...
that is to say if the pinis just slim enough that it can be pushed in and taken
out dry with the fingers, then the holes are obviously oversized. The (very thin)
epoxy can find its way up the sides of the pin to form and allowed to form a
collar at the top. Clean off as necessary. Judicious use relative to the amount of
epoxy put into the whole limits overflow / waist. One little trick that takes care
of this and any bleed off into neighboring holes is to use a piece of piano wire
to gauge how deep the hole is... which tells you how much epoxy you need to drip
in.  Pins being of the same length then will then end up << bottomed out >> in the
epoxy and will be one hundred percent solidly coupled to the bridge on all
surfaces. Cant hurt me thinks.

As will every thing... practice makes perfect and you get the hang of how to
accomplish this one successfully fairly easy. But what I like most is the long
term. Seems to stay solid for like ever. Getting a pin into an undersized hole
without damaging the wood in one way or another is a good trick, and one that it
would seem to me easily takes as much time and carefullness as dealing with the
kinds of problems the epoxy solution presents.

When so many types of falsness are so easily curred by CA treaments, or epoxy
treatments, it seems to me like a good idea to begin this way. Especially when the
end result seems to last quite a bit longer.

>
> So it seems to me that the first thing you need to decide is if you want
> the pin bottomed in the hole or not.
>
> Ron N

This way you dont have to make that decision, tho the pin ends up bottomed out in
the epoxy. I'd like to know what this concern about the epoxy soaking into the
wood is all about tho.

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