Pianotech

  • 1.  Grand Bridge Repair

    Member
    Posted 05-14-2018 10:03
    Looking for some suggestions from anyone that has had experience with the following type of bridge repair. The long bridge on a grand has separated at the splice in the bridge root. I tried to take some pictures to show this but was not very successful. I need to glue the splice back together and then repair the bridge pins.

    Questions:
    1. Suggestions for procedures to repair the bridge splice.
    2. Suggestions for type and application of glues for the repair.

    I will be repairing the pulled bridge pins with epoxy. That is a repair that I have done before and am fairly comfortable with. 

    Thank you in advance for any help that you can provide.
    If this was not clear, let me know and I will provide more information.

    Thank you.

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    Rex Roseman
    Roseman Piano Tuning
    Akron OH
    330-289-2948
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  • 2.  RE: Grand Bridge Repair

    Registered Piano Technician
    Posted 05-14-2018 10:20
    Rex,

    Broke at the/a splice in the long bridge, you say? Bosendorfer? Yamaha? Other? Was the bridge attached to the soundboard when it broke? But the cap (if there was one) survived?

    Alan

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    Alan Eder, RPT
    Herb Alpert School of Music
    California Institute of the Arts
    Valencia, CA
    661.904.6483
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    Original Message


  • 3.  RE: Grand Bridge Repair

    Registered Piano Technician
    Posted 05-14-2018 10:27
    Hi Rex, consider the forces that created the separation in the first place when you formulate your repair.
     
    Bridge root  ..........  the part under the bridge cap??
     
    Some pix would be great.  I'll take a stab at this using the best of my imagination.
     
    Some people add hidden screws to fix bridges.  I'd expect this will be what you'll have to resort to.  Another fix would be to drill a hole all the way through the break in such a way that a nut and bolt combination would clamp the pieces together until the wood epoxy sets up.  Then remove the bolt, plug the hole with a hardwood dowel, dag and finish as required, reinstall the strings and tune for a few days.
     
    Six months from the repair date may make you look bad.  I've had bridges fail in the exact same place after a repair.  From that point on, the repair is a donation  .........  or an educational expense.
     
    Lar
     
     



    Original Message


  • 4.  RE: Grand Bridge Repair

    Posted 05-14-2018 10:51
    I assume this is a scarf joint. Remove a few strategic wires and bridge pins. Drill a few ¼" holes. Use 3/16" bolts w/buttons to draw the joint closed. After you insure a dry fit, glue with epoxy.  When cured, remove the bolts and install ¼" dowels. An alternative would be to install a bolt so that the threads help to maintain the closure; countersunk from the top or with the head exposed underneath and plug the top hole in the cap.

    You might drill to 3/16" and use ⅛" bolts. The hole just needs to be larger than the shank to allow for the two surfaces to mate and not have the shank bind in the hole restricting closure.

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    Regards,

    Jon Page
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    Original Message


  • 5.  RE: Grand Bridge Repair

    Posted 05-15-2018 06:50
    Are there strings on the piano? Can the plate be removed easily? It sounds like maybe no, so I'll make that assumption. I have not done this exact repair previously, but I do have a good bit of experience working with wood and epoxy (and butt joints - but like Jon suggests, this is likely a scarf joint - a kind-of modified butt joint).

    I think Jon's approach is likely best if the bridge cap is not to be removed. Epoxy, when used properly can make a joint like this stronger than the wood itself. However, the problem is that there is going to be glue residue in the joint from the original assembly. Epoxy forms a mechanical bond to the bonding surfaces. If that surface is some sort of smoothish plastic-like glue surface, it might not bond very well at all. Ideally, one would be able to run a saw into the separation and clean all the old glue out. Then you could use something like the West System two-step bonding method for a superior bond.

    But assuming you can't clean out the joint (can you? is there access?), you may want to have some sort of permanent mechanical clamping put in place as Jon suggests. Make sure the bolts run through the scarf in several places. You will likely want to put a strip of good hardwood on the bottom of the soundboard to prevent pull-through. You may well have some significant forces trying to separate that joint - and thus, you may need some significant force to clamp it back together!

    So to sum up: Drill several holes through the bridge joint from the top of the cap through the bottom of the soundboard (hopefully there is not a rib in the way) large enough for the bolts to pass without significant resistance. Cut 1/4" to 3/8" thick hardwood (or steel!) backing plate (with  holes extending through plate). Counter-sink holes in cap. Slather joint with epoxy (West System two-step would be optimal). Run bolts into holes, install nuts (w/ washers if using hardwood) and tighten.

    That's what I'd likely do. I tend to over-engineer things when I'm not sure what it will take to do the job. And here is an example of a task that you really only want to do once and not have it fail.


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    Terry Farrell
    Farrell Piano Service, Inc.
    Brandon, Florida
    terry@farrellpiano.com
    813-684-3505
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    Original Message