capo-hardening?

[Ed Sutton]

Roger-
    When I think about how easy it is to drill through the plate once the
drill bit breaks through the skin, and how thin 1mm is, I thank my guardian
angel for keeping me -very- light handed with file and abrasive paper!  I
hadn't really thought about how different the bearing surface is from the
rest of the plate.
    And this would mean that if the plate was heavily filed during the first
fitting, there might be much less than 1mm case hardening remaining, or even
that the original bearing surface could have been soft iron. Yes?
    Would this be more likely to happen at the section ends? My impression
is that the first capo note is the most prone to zings.
    I have a very vague idea of how sand casting is done, and no idea of
what V pro casting is.
    Keep the "trivia" coming. Maybe we can get another article from you?
    Thanks!
    (By the way, I've not heard from Nina this morning)
        Ed S.

----------
>From: jolly roger <baldyam@sk.sympatico.ca>
>To: caut@ptg.org
>Subject: Re: capo-hardening?
>Date: Mon, Sep 24, 2001, 12:46 AM
>

> 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
>
>