Bridge Repair (was 30 minute epoxy)

[Gregory Torres]

Robert,

I have used the marine epoxy you refer to for repairing bridges as well, but I
thin the epoxy with a little bit of acetone and mix in some maple sawdust. It
has worked very well for me.

Regards,
Greg Torres

Robert Goodale wrote:

> Glen_Deligdisch@sil.org wrote:
> >
> >      Willard Leverett in his video "Piano Bridge Repair Made Easy" showed
> >      him using a 30 minute epoxy to fill the tinny hairline cracks in both
> >      a treble and bass bridge.  The epoxy he was using was very watery and
> >      therefore was good at soaking deeply into the wood.
> >
> >      Do any of you have suggestions where one would look for the watery
> >      variety?  All I have been able to find is epoxy with the consistency
> >      of honey.
> ---------------------------------------------------------------
>
> Glen and List:
>
> I realize that several others have already touched on this, but I'll
> pitch in my two cents worth (no pun intended), for what it's worth.
> "Free flow of information and knowledge", that's my philosophy!
>
> Ok, for split bridges/loose pin problems on any high-quality instrument
> I immediately recommend a recapping job. It looks neat, it's
> professional, and its the right thing to do. There are many occassions,
> however, when we encounter lower quality instruments or customers that
> are not yet ready to invest in a full rebuilding. In such situations we
> are often required to "Repair" such bridges.
>
> Assuming the bridges are not "beyond all hope" and split deeper than a
> California fault line, the first and obvious step is to de-string the
> instrument (or section of bad bridges on less severe cases). Pins must
> be pulled out carefully. Some remaining tighter pins may take some
> splinters with them if care is not taken. Except in some more minor
> sectional repairs, I replace all the pins with new, particularly if I am
> repining an entire bridge. Pins are cheep, easy, and look more like a
> professional repair. I recommend the long pins sold by Pianotek (p.
> A-18). The shorter pins sold by many other suppliers usually bottom out
> in a old bridge hole making it more difficult to achieve a solid-fitting
> pin. DO NOT replace loose pins with the next larger size. Unlike tuning
> pins, each size bridge pin is considerably larger than the previous
> size. All you will accomplish is split the bridges worth.
>
> In terms of epoxies, I highly endorse the "West System" (by Gougeon) 105
> Resin with the 206 hardener. This is also available from Pianotek (p.
> B-19), however here's a hint: It is also available over-the-counter at
> many marine supply stores for less money. If they don't have it, inquire
> about price to order it. You can also check out their Web page at:
> http://www.westsystem.com/
>
> West System 105 has the fantastic advantage of being increadably thin in
> viscosity. It soaks deep into the wood like a spong filling microscopic
> cracks and splits you didn't even know were there. At the same time it
> has just enough body that it still remains manageable. When cured it is
> absolutely glass-hard, critical for positive transfer of vibrative
> energy. Many epoxies cure suprisingly soft, particularly the so-called
> 30 minute varieties. No offense to those who use these types of epoxies-
> I use them as well, just NOT for bridge work.
>
> ***FYI, Gougeon also makes a really great fast-cure epoxy for "other"
> uses- #865-B epoxy and 865-B hardener. Also available from Pianotek, but
> check the marinas for this too.***
>
> If there are any larger splits in the bridge, two applications will be
> neccesary, the first to fill the cracks followed by all needed
> filing/shaping and sanding, and the second for the pin holes. Epoxying
> the new pins into the holes will insure a long-lasting reliable repair
> with no loss of vibration between the pins and the bridges.
>
> Likely before this step is taken you will want to LIGHTLY sand down and
> smooth out the bridge tops. (be careful not to change downbearing). You
> can also clean out the notches while your at it. At this point the tops
> will need a new application of "dag", (one of those fun words no-one
> knows the origin of - or cares). Traditionally dag is made from grafite,
> but I much prefer gray Teflon (Pianotek P. B-18). Use a small artist
> brush to apply. A couple of coats may be neccessary. Follow this by
> burnishing the tops with a thick soft cloth or a piece of hammer felt.
> The result will be a beautiful shiney finish virtually identical to
> graphite, but with half the effort and no mess. It looks even better on
> new bridges.
>
> I have seen technicians use a variety of ways to apply the West System
> 105 to the pin holes. One popular method is to simply dip a piece of
> heavy music wire into epoxy and dribble it into the hole. A way that
> works faster and more effecient that I have discovered is using a
> hypo-oiler bottle. Use the large sized bottle. West System 105 is quite
> thin when first mixed and can be applied easily in this manor, but you
> do have to work fast. After about 10-12 minutes it thickens enough that
> this becomes more difficult. The epoxy MUST be very well mixed or it
> will not cure evenly- I don't know why, it just does. After mixing for
> several minutes, quickly pour the mixture into the hypo bottle and go to
> work. I like to wrap the bottle in a piece of medium felt cloth (to
> protect the plastic bottle), and then hold and squeeze the bottle with a
> pair of channel-lock pliers. Quickly move from one hole to the next all
> the way down the bridge until a adequate amount of epoxy has been
> ejected into each pin hole. Note that if too much is injected it will
> squeeze out in a big mess when the pins are inserted. Too little may not
> do the job- you will have to experiment.
>
> Once all the holes have been epoxied you need to immediately empty and
> clean the hypo-bottle. The pins can wait till afterward, the epoxy will
> not harden for many hours so you have a little time at this point. Fill
> and rinse the bottle several times with acetone. If epoxy hardens in the
> needle, blow it out with compressed air and/or insert a small piece of
> music wire, followed by a good rinsing with acetone. The bottle can last
> a long time if it is properly cleaned after each use.
>
> The pins can now be inserted into the bridge. I like to tap them in with
> a piece of brass rod with a small dimple on one end to protect the
> copper plating. It is likely that some epoxy will ooze out when the pins
> are inserted. This can be flossed out with a rag and a small dry brush
> after all the pins are installed, repeating several times with fresh
> clean rags. If there is any substancial remaining residue, it can be
> loosened and cleaned with a small artist brush dipped in acetone follwed
> by a dry rag. This may take some of the "dag" off, however, so some
> manual touch-up may become necessary.
>
> Once the epoxy has cured the tops of the pins can be filed flat for a
> professional and cosmetically appealing look. A file may be neccessary
> in tight areas, but I simply take a belt sander with a fine belt and run
> it across the bridge tops. Obviously this requres a great deal of care-
> don't go crazy. Keep the machine moving so that the pins don't get too
> hot. This procedure is actually easier than it sounds. Do a bit of
> touch-up with a file, clean things up a bit, and your home-free.
>
> I first learned this procedure from a very sucessful and proven
> technician in the mid-west who specializes in bridges and soundboards (I
> won't mention names here but you can e-me privately). My personal
> experience with it has yielded great success numerous times, however I
> will admit that it took several jobs before I perfected my technique.
> Hopefully it can bring you success as well.
>
> Best wishes
>
> Rob Goodale, RPT