[CAUT] bridge-pin experiment-Oops!

[Ed Sutton]

(Sorry, meant this to go to Mark...which it did, along with everyone else.  Happy New Year!  Ed)

----- Original Message ----- 
From: Ed Sutton 
To: College and University Technicians 
Sent: Monday, December 31, 2007 1:16 PM
Subject: Re: [CAUT] bridge-pin experiment


Hello, Mark!
You've got the outline of an article here.
Would you like to develop it and take photos?
Or, would you be willing for me to assign it to someone, to develop and take photos, then publish with both of you as co-authors?
We have some lab research on false beats being written into articles. It would be good to publish a repair article when we publish the research on false beats and bridge pins.
Ed Sutton
  ----- Original Message ----- 
  From: Mark Cramer 
  To: CAUT 
  Sent: Monday, December 31, 2007 12:50 PM
  Subject: [CAUT] bridge-pin experiment


  Happy New Year to all!

   

  While in Banff earlier this month, I made an experiment I'd wanted to try for some time, comparing the relative penetration of epoxy and CA glue in treating loose bridge-pins.

   

  In brief, I installed about a dozen bridge-pins into sample stock, then twisted them out and re-installed them to "loosen" the fit. I applied CA to ½ of them, and epoxy to the rest, with some black dye added, as a "tracer." 

   

  Note: The epoxy was West System, and I heated the bridge-pins with a soldering iron (a tip from Joe Garrett that's stood the test of time) to help the epoxy penetrate.  

   

  The next day I removed the bridge pins and ripped the stock through the hole-centers to check the results. All pins were now extremely tight!

   

  Overall, both products penetrated the holes to a depth of a1/4" or more, which by Ron Nossaman's good advice, should be plenty.

   

  Both products also seemed to fill the void well, leaving a precise half-mold of the bridge-pin, that is, when the material hadn't pulled away with the actual pin. 

   

  I noticed a little difference in the two resins however; the epoxy was a solid opaque deposit, while the CA was more cellular, sometimes with tiny voids or bubbles between. If you've used these products however, you will already be familiar with these characteristics, and neither seems to suffer in holding ability as a result.  

   

  (Secretly, I had been cheering for the epoxy, on the presumption that the thickness of the resin (once it cooled) would make a better gap-filler in the long term.)

   

  I used a 20X jeweler's loop to examine, and no, I didn't take photos.

   

  In terms of application, the CA was the winner. Using a syringe, it's possible to mete out thin CA very precisely; watching it disappear around the pin, then adding more. If you overdo it a bit, it can easily be drawn back into the syringe, leaving a very tidy, clean surface. (We've frequently taken advantage of this property to treat bridge-pins with strings in place) 

   

  The epoxy however, seemed to leave a small collar around the base of the pin. With practice, I was able to get the collar small enough that it wouldn't contact my test-string (#16 wire), however, I don't know if I would have the courage to apply epoxy with strings in place.

   

  In conclusion, this wasn't a very scientific experiment, but it was about all I had time for, and it answered my questions just fine.

   

  As a result, we will continue to use thin CA to treat loose bridge-pins, with strings in place. The application is easy, the results (correcting false beats) have been good, and now we know the glue is making it well below the bridge surface. BTW, I still believe it's better to saturate one pin at-a-time, then doing a whole section in a series of passes, at a risk of "sealing" the hole on the first pass.

   

  For re-pinning a bridge, we've been using Bill Spurlock's epoxy method (PT Journal, March 1992) for over a decade and will not change a thing. Joe Garrett's method however, is still the best I can think of when you have to re-use a bridge-cap that needs some reconditioning, especially when they start to get tiny splits and visible voids.

   

  Now here's a challenge I've perhaps thrown down before:

   

  If you've never tried to deal with false beats, (or are holding to some noble albeit untested notions ;>) why not treat yourself to a rewarding little experiment?

   

  The next time you're tuning an old practice-room grand and encounter a false beat, isolate the string (by muting the other two) then gently rest a screwdriver on the forward bridge pin and see whether the false beat stops. If so, you have a candidate.

   

  If you want to experiment with the string in place (and why not.you're the same person who has to fix it :>), test your syringe technique outside the piano first, then carefully apply CA to the base of the pin, on the non-string side. Apply drop-by-drop, wait and watch, then continue until the pin won't take anymore. Withdraw any excess glue with the syringe. 

   

  I would actually wait awhile before tuning, as we don't know how long the glue takes to cure below the surface, however you can likely go back in an hour or so and simply "listen" to the results. As mentioned earlier, we've been using this method for several years, with good success.

   

  Best wishes,

  Mark Cramer,

  Brandon University

   

        

   

   

      

   

    
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