Fwd: Re: capo-hardening?

[jolly roger]

>Date: Mon, 24 Sep 2001 00:46:56 -0500
>To: caut@ptg.org
>From: jolly roger <baldyam@sk.sympatico.ca>
>Subject: Re: capo-hardening?
>
>Hi Ed,
>           The case hardening from the quenching is typically less than
1mm deep, so it does not take too much dressing to file through it.  The
grey cast iron (sand cast) is quite soft on the inside and is easily ground
by the abrasion of the strings just pulling to pitch, so the case hardened
skin is important to longevity. 
>   V pro plates are a different story, with a lot of different
characteristics.  The additives to enable rapid cooling makes the material
less pourous, and also less prone to wear that the core material of sand
cast.  V pro is not case hardened in the same sense as grey cast, since no
quenching takes place.  Heat is removed quite rapidly through conductivity
into the large steel molds.
>Complete cooling time is about 40mins vs hours with the sand cast process.
>So you are fairly safe filing and dressing a C3 plate.    
>
>Some of the keys to making a good sand cast plate.  Sand mold is good and
wet to effect quenching, and case hardening.   Slow rate of cooling to
ensure good stress relief, and to minimize distortion.   I seem to recall
that 24hrs cooling for the best concert grand plates, before the plate is
taken from the mold.  May be wrong on the time, but it is very slow.
>
>More trivia. <G>
>Roger
>
>
>At 10:26 PM 9/23/01 -0500, you wrote:
>>Mark-
>>I've tried burnishing the capo after dressing with file and emery paper. It
>>didn't do any harm, the section sounded clear, but this was just as part of
>>restringing, it was not a piano with zingers.
>>I've wondered how to test whether burnishing would produce enough work
>>hardening to make a difference.
>>Perhaps your piano would provide a test.  If you can get the strings out of
>>the way, an etcher's hook burnisher should fit under the capo bar with the
>>plate in the piano.  I suppose it's a long shot, but not hard to do.
>>I have a C-3 with zingers coming up in a few weeks. I hope you can give us
>>the answer by then!
>>Ed S.
>