Bass bridge puzzler

[Farrell]

I made a new bass bridge a few weeks ago from quarter sawn hard maple and I made a cap of three, 3 mm-thick, quarter sawn hard maple laminates which were epoxied together and epoxied onto the bridge body. The individual laminates are arranged at slight staggered angles, but are roughly kept close to parallel to the long axis of the bridge. I haven't strung the piano yet (hopefully within the next week or so), but I sure as heck expect the bridge to not split in two! It is quite easy to build a bridge in this manner and I believe the epoxied laminates will greatly decrease the possibility of splitting. I have also found such a cap to be nearly as easy to notch as a solid cap. I just finished notching the long bridge which has a cap of five 2 mm-thick laminations. Notched real nice. The laminations are kinda nice for the beginner notcher as they provide a visual guide for consistent notch depth, angle and general shape!

Terry Farrell
  
----- Original Message ----- 
From: "Dave Nereson" <davner@kaosol.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Monday, May 26, 2003 5:12 AM
Subject: Re: Bass bridge puzzler



  ----- Original Message ----- 
  From: Mike Kurta 
  To: PTG List 
  Sent: Sunday, May 25, 2003 6:49 AM
  Subject: Bass bridge puzzler


      Hi Gang:
      Two weeks ago, I duplicated a bridge for a local tech from a 10 year old Baldwin console which had split in the usual manner.  After installation and attempting to pull the bass strings up to pitch, the new bridge split again down the pin line on the speaking length side of the bridge.  Will now have to make another, but don't want to have the same result.  
      A few points:  Hard rock maple was used, the dimensions, pin size and positioning were all closely duplicated, and finished with DAG along the top.  Grain orientation was followed according to PTG information.  The new bridge failed the same way as the original one.  We did not measure downbearing, felt there was no need.  
      We are looking at some possibilities:  1.  I used the entire length of the new pin into the wood, did it weaken the bridge along its length?  Did the pins drive in too tightly starting the split?   Was there a flaw in the wood?  I havn't seen it yet, so will examine.  Should I use smaller diameter pins next time?  Should they be angled more toward the center (each other) at the bottom of the bridge?  Was there a design flaw in the original bridge we are repeating?  
      Any ideas?  HELP !  
      Mike Kurta

  Maybe the wood wasn't cured.  I had one duplicated by Schaff that split despite all my precautions.  I suppose it's possible that bridge pins driven in too hard might help it split.  I've had even soft pine split when driving in nails, even when I pre-drilled a hole for the nail.  This happens more often at the end of a board than in the middle.  Maybe if both the sides and the end were clamped somehow while driving pins . . . or use one drill size larger?
      --David Nereson, RPT