Epoxy Bass Bridge Repair

[Gregor _]

Aaaahhh, NOW I understand. Had problems due to language misunderstandings. Thank you very much, Terry.

Gregor

From: mfarrel2 at tampabay.rr.com
To: pianotech at ptg.org
Subject: Re: Epoxy Bass Bridge Repair
Date: Sat, 10 May 2008 21:00:30 -0400










Sorry, but I still don´t understand that statement. A 
thin layer of Epoxy to remain in the joint? Of which joint you are talking 
about: the joint of Epoxy and wood?
 
That's okay - we'll poke away at it 
until you do understand!  ;-)
 
All that I was trying to point out is that 
most glues (like Titebond) work best with a close-fitting joing - two wood faces 
that meet nice and flush with one another - when they are clamped together, you 
want significant clamping pressure and most of the glue to squeeze out. With 
epoxy, you want just the opposite - the two faces of wood to be bonded together 
need not fit together perfectly (in fact better is the joint is a little rough 
or jagged) and when you clamp, the clamps are just to hold the two wooden faces 
in position - not to apply pressure to squeeze the epoxy out - you want to leave 
some epoxy in the joint between the two wooden faces to be 
bonded.

What does it mean for practice? Should I first apply a 
little bit of Epoxy to the wood, let it become hard, and then apply the Epoxy 
with the filler?
 
No. Read on the West System web site about their 
two-step bonding process:
 

Two-step 
bonding


  
  
    1. Wet-out 
      bonding surfaces-Apply a neat resin/hardener mixture (without fillers) to 
      the surfaces to be joined (Figure 9). Wet out small or tight areas with a 
      disposable brush. Wet out larger areas with a foam roller or by spreading 
      the resin/hardener mixture evenly over the surface with a plastic 
      spreader. You may proceed with step two immediately or any time before the 
      wet-out coat reaches the final cure stage.


  
        
  
    2. Apply 
      thickened epoxy to one bonding surface. Modify the resin/hardener mixture 
      by stirring in the appropriate filler until it becomes thick enough to 
      bridge any gaps between the mating surfaces and to prevent "resin-starved" 
      joints. Apply enough of the mixture to one of the surfaces, so that a 
      small amount will squeeze out when the surfaces are joined together with a 
      force equivalent to a firm hand grip (Figure 10).

      Thickened epoxy can be applied 
      immediately over the wet-out surface or any time before the wet-out 
      reaches its final cure. For most small bonding operations, add the filler 
      to the resin/hardener mixture remaining in the batch that was used for the 
      wet-out. Mix enough resin/hardener for both steps. Add the filler quickly 
      after the surface is wet out and allow for a shorter working life of the 
      mixture.


  
    3. Clamp 
      components. Attach clamps as necessary to hold the components in place. 
      Use just enough clamping pressure to squeeze a small amount of the epoxy 
      mixture from the joint, indicating that the epoxy is making good contact 
      with both mating surfaces (Figure 11). Avoid using too much clamping 
      pressure, which can squeeze all of the epoxy mixture out of the 
      joint.


  
        
  
    4. Remove 
      or shape excess adhesive that squeezes out of the joint as soon as the 
      joint is secured with clamps. A wooden mixing stick with one end sanded to 
      a chisel edge is an ideal tool for removing the excess (Figure 
    12).
 
Make sense?
 
I hope this helps you.
 
Terry Farrell

  ----- Original Message ----- 
  From: 
  Gregor 
  _ 
  To: Pianotech List 
  Sent: Saturday, May 10, 2008 5:05 
AM
  Subject: RE: Epoxy Bass Bridge 
  Repair
  
Sorry, but I still don´t understand that statement. A thin 
  layer of Epoxy to remain in the joint? Of which joint you are talking about: 
  the joint of Epoxy and wood?

What does it mean for practice? Should I 
  first apply a little bit of Epoxy to the wood, let it become hard, and then 
  apply the Epoxy with the filler?

Gregor


  
    
    From: mfarrel2 at tampabay.rr.com
To: pianotech at ptg.org
Subject: Re: 
    Epoxy Bass Bridge Repair
Date: Fri, 9 May 2008 15:57:38 -0400


    
    

    Some adhesives like Titebond are not very good 
    at filling gaps. They perform best with a tight-fitting joint and minimal 
    glue left in the joint. Epoxy and many other adhesives is gap filling and 
    you want at least a thin layer of epoxy to remain in the joint - doesn't 
    have to be much, but you don't want a perfect fitting joint and then apply 
    high clamping pressure. With epoxy you want a loose fitting joint (or 
    roughened up surfaces) and minimal clamping pressure - clamp pressure is not 
    to "clamp" as such, but rather simply to hold pieces in place.
     
    Terry Farrell
    
      ----- 
      Original Message ----- 
      From: 
      Gregor _ 
      To: 
      Pianotech 
      List 
      Sent: 
      Friday, May 09, 2008 11:49 AM
      Subject: 
      RE: Epoxy Bass Bridge Repair
      
Terry,

what do 
      you mean by "you need 
      to leave some epoxy in the gap. You don’t want to 
      epoxy-starve the joint."?

I found a source for Western System Epoxy 
      handy repair set including that filler here in Germany. Good to know, I 
      will try it perhaps one day, but not with that Kawai. I told the customer 
      to ask a collegue who has 7 pianotechs working for his shop: 4 on master 
      level, 2 with certificate of apprenticeship and one apprentice, and they 
      have a huge workshop. I don´t do repairs with woodwork anymore, just 
      tuning, small repairs and selling pianos. But in this case it probably 
      would have been easier to order a new brigde from Kawai which fits 
      perfectly without any adjusting: just installing and it 
      fits.

Gregor


      
        
        From: mfarrel2 at tampabay.rr.com
To: pianotech at ptg.org
Subject: Re: 
        Epoxy Bass Bridge Repair
Date: Fri, 9 May 2008 08:57:04 -0400


        

        Epoxy repairs for a situation 
        as you describe can yield very good results. Sometimes the crack opens up a fair bit – you’ll want 
        to clamp it back into position – not to 
        clamp in the traditional sense, but rather to simply position 
        the parts in their original orientation – 
        you need to leave some epoxy in the gap. 
        You don’t want to epoxy-starve the joint.
 
I use West System epoxy 
        resin, hardeners and fillers:
www.westsystem.com My 
        favorite for a cracked bridge is #404 High-Density Filler and using the West System two-step bonding 
        procedure described on the West System web site. The following is from 
        the West System web site:
 
404 High-Density Filler
404 High-Density 
        filler is a thickening additive developed for maximum
physical 
        properties in hardware bonding where high-cyclic loads 
        are
anticipated. It can also be used for filleting and gap filling 
        where maximum
strength is necessary. Color: 
        off-white.
 
You can either push the 
        bridge pins into the uncured epoxy, tidy up and be done with it, 
        or, for a neater, more exacting job, you can epoxy the gap and then 
        drill bridge pin holes after the epoxy hardens. I have found that if 
        cosmetic considerations are not paramount, I apply the epoxy, clamp 
        together until the wood is close to original dimension, clean off epoxy 
        squeeze out (acetone) - at that point you will be able to see the 
        outline of the original pin holes - push pins in place - the wood will 
        have been drawn together enough to hold the pin in its original position 
        - and then level off and clean up the little bit of epoxy that squeezes 
        out of the holes as you push the pin in place. Wait a day or two for the 
        epoxy to completely cure, go back and install bass 
        strings.
 
I've done this repair numerous times with great 
        success.
 
And of course, on a nicer piano where the budget 
        allows, new bridge and/or new cap is preferred.
 
Terry 
        Farrell

        
          ----- 
          Original Message ----- 
          From: 
          Gregor _ 
          To: 
          pianotech at ptg.org 
          Sent: 
          Friday, May 09, 2008 5:13 AM
          Subject: 
          Epoxy Bass Bridge Repair
          
I crawled the archieves but I did not really find what 
          I was looking for: does Epoxy work even for bigger gaps?

I 
          wanted to tune a Kawai CE-11 upright yesterday but the bass bridge 
          looked horrible: a long gap which affected 9 notes. The gap started at 
          the upper pin row and the pins were vertical. Some strings rattled at 
          the pins. The gap expanded up to 4 mm above the upper pin row. I did 
          not try but I could imagine that I could have pulled out some pins 
          without using pliers.

First at all: I never worked with Epoxy. 
          My first thought was to pull out the pins, fill the gap with epoxy and 
          drill new holes for new pins. Could that work or is such a gap too 
          much for Epoxy? The bridge is made of one piece of wood, no 
          cap.

I was shocked about such a gap in a Kawai from 1992 (no 
          grey market import): no floor heating, no air con and no heater near 
          by the piano. And I don´t live in an area with huge differences in the 
          climate. Very strange. That damage is a pitty because everything else 
          in this piano was in a pretty good condition. But making a new bridge 
          would be definitely too expensive including transports from the second 
          floor into a workshop and back to the 
        customer.

Gregor

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