another cracked plate question

[Carl Meyer]

I don't have any real experience with welding cast iron, but I will relay
what Gary from Lock-n-stitch had to say in a class given at Bob Davis' shop
in Stockton.

"The way to weld cast iron is to heat the complete item to 1200 degrees,
weld at that point and cool slowly over 6 hours.

Depending on location some welds are impossible due to the expansion,
shrinkage, and hardening that occur.  Example,  a spoked cast iron wheel
when welding a spoke will expand while welding and then shrink, pulling the
joint apart.  Then due to the hardening that occurred without proper
annealing it becomes brittle and will likely crack at the point the annealed
portion meets the hardened part.  Perhaps the new crack was caused by the
old repair.

I have successfully repaired a couple of plates by splinting.  I wish I had
taken pictures.  On one occasion, the crack was caused by poor mounting of
the plate to the pinblock, adding stress in the
worst direction possible.





----- Original Message ----- 
From: "Bob Hull" <hullfam5@yahoo.com>
To: <pianotech@ptg.org>
Sent: Sunday, March 28, 2004 8:57 PM
Subject: another cracked plate question


> I have read all most of the cracked plate subject
> archives and still don't have quite the info I need.
> So, any thoughts would be appreciated:
> This week I went to tune a Baldwin A (about 33 years
> old) and found it a half step low.  It had been many
> years since any previous tunings.  The customer showed
> me 3 places where the plate had cracked and been
> repaired while the piano was quite new.  So figuring
> the repairs had held all of these years I set out to
> bring it up to pitch, still carefully.  I did not
> overshoot 440 but planned to tune it up to 440, see
> where it dropped back and tune it there.  During the
> process, only raising the pitch about 20 cents at at
> time, I found another crack in another place about two
> inches from a repaired crack.  I don't think it was
> there when I started.  At that point I informed the
> customer and abandoned my tuning. I said I would get
> back with them about what to do.  They are quite
> attached to this piano.
>
> Since it has been cracked and repaired before and now
> there is another crack, do you think that repairing
> this crack would be futile because it is just a weak
> plate?
>
> Could I find another plate that could be used?  The
> previous repairs are bulky and messy looking welds
> which the customer doesn't like the appearance of.
>
> Bob Hull
>
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