Bass bridge puzzler

[Dave Nereson]

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  ----- Original Message -----=20
  From: Mike Kurta=20
  To: PTG List=20
  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. =20
      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. =20
      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? =20
      Any ideas?  HELP ! =20
      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
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