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

[Farrell]

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Comments below:
=20
> Terry Farrell wrote
>=20
> > >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
> > >=20
> Why would a (very) little epoxy absorbing into the wood be a problem ?

If the bridge pin is only a tad smaller than the hole, there will only =
be a small volume of epoxy filling any void space between pin and wood. =
If the wood absorbs the epoxy, then there will be none or little epoxy =
filling the void by the time it cures. Just a concern.
=20
> > Ron Nossaman wrote:
>=20
> > 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.
>=20
> 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.
>=20
> 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.=20

Another thing to keep in mind with epoxy - it relies on a mechanical =
bond between wood and epoxy and between metal and epoxy. It is =
recommended by West System that when bonding with epoxy to metal that =
the metal surface be sanded rough, coated with thin epoxy, and the epoxy =
sanded into the metal for the most secure bond. A nice new shiny bridge =
pin is not likely to establish a good bond to epoxy. I can chip epoxy =
off any glossy surface real easy when I get waste on it - my floor, =
table top, etc.

Terry Farrell

> 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.
>=20
> 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.
>=20
> >
> > 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
>=20
> 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.
>=20
> Cheers
> RicB


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