Bridge Root Spring-Forward

[MICHAEL MORVAN]

Terry,
    I don't make bridge roots but I do a lot of research on glue and it's effects on wood to try and improve my more complex key repairs and recovering. First of all:

1. What type of glue did you use, PVA? if so, too much moisture, it takes a very long time for this type of glue (with a lot of water content, upwards of 60%) to dissipate from the wood and the curve will continue to change as this happens.
2. Thinner laminations (18 laminations) actually add more moisture to the joint because there are more joints to apply glue to.
3. How were your laminate surfaces prepped? Jointed, bandsawed, sanded, hand planed? 
4. Did you heat the laminates, heat if possible will accelerate drying time which will prevent some of the warping due to time lapse as the moisture flashes off.
5. Urea, polyurethane, epoxy and resorcinol glues have good creep, rigidity and are more than strong enough for bending laminates. The biggest plus is that they don't have the high moisture content that temporarily haunts all glue joints.
6. The Glue Book by William Tandy Young (Published by The Taunton Press) has a chapter on laminates and veneering which is a wealth of knowledge, for cheap money.

These are just my thoughts and opinions, I don't claim to be an authority on laminating bridge roots, by the way, what the hell is a bridge root? Must be something you belly people make.  Good luck,   Mike

Michael A. Morvan
Blackstone Valley Piano
Dedicated To Advancing The Art Of Keyboard Restoration
76 Sutton Street
Uxbridge, Ma. 01569
(508) 278-9762
Keymaestro at verizon.net
www.pianoandorgankeys.com                                                                                              



  ----- Original Message ----- 
  From: Farrell 
  To: pianotech at ptg.org 
  Sent: Wednesday, September 05, 2007 1:44 PM
  Subject: Bridge Root Spring-Forward


  Question for those who are in the habit of laminating up new bridge roots - or maybe even those who don't, but might have some thoughts to share. I just completed building a bridge root for a customer that came out very nicely, but the overall curve of the bridge is off by a couple millimeters or so, much like other ones I have built in the past. I really don't understand that. 

  One would think of the possibility of some small spring-back effect (but with 18 laminations?), but the curve error is always toward a tighter curve. How can that be? 

  I don't think it is a significant issue as you can easily correct the bend with your pinky - but still, how does this happen?

  A couple pics for your viewing pleasure:







  Terry Farrell
  Farrell Piano

  www.farrellpiano.com
  terry at farrellpiano.com
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