>But if brass is softer than the steel music wire, and I presume
>softer than unhardened cast iron, then isn't the steel wire going to
>cut a groove into the brass capo insert? And isn't that what we're
>trying to avoid?
>
>Terry Farrell
Terry and all,
Indeed, that's exactly what happens, and yes it is what we are trying
to avoid. There will be considerable variations in the drawing and
treatment of various alloys, which is bound to result in considerable
hardness variations. Some may be harder than unhardened cast, but I
don't believe any are really suitable for supporting piano wire,
because they are relatively too soft. I'm not a big fan of using
other alloys for the capo, and I have replaced them a couple of times
with hardened silver steel (which in its cheapest form is a straight
high carbon alloy, and its not necessary to use the more expensive
oil-hardening grade) with much improved results.
I can say from experience that the modern capo, if not hardened, is a
disaster on account of its softness. As I have written previously, I
suspect that this phenomenon of so much noise may be in part due to
the longer freeze times which result from modern foundry practice -
where two-pack chemical binders are typically used for the moulding
sand and the mould is drier before the castings are poured. Overly
long front counter-bearing lengths are as much to do with the
problem. Our colleague Ron N. has also written about this in this
thread.
Despite the fact that cast iron doesn't have as favourable a friction
coefficient as some of the other alloys, when bearing against piano
wire, the grooving that occurs with other alloys makes them also drag
during rendering. While unhardened cast iron is not very good either,
when properly hardened (there is hardening and hardening), the
strings will render at five years just like the day that the piano
was strung. I know this because I've been doing it for enough years,
and following up our own instruments on a regular basis to know that
it is a fact. The tone will still 'age' when the bar is hardened
because tonal deterioration is a result of both bar and wire
deformation, but the deterioration is less when an appropriately
radiused and hardened bar, with appropriate string approach angles
are used.
As I've written previously, care has to be applied with regard to
maximum string approach angle and not making the bars too small in
radius (which I have to avoid a propensity to do, in search of that
really clean tone), but provided a commonsense approach is used, I
believe hardening is a worthwhile practice for quality tone building.
Yesterday one commentator said
>
>>Why do manufacturers harden capo bars...
>
>Do they? How? Cast iron is hard anyway.
Modern cast plates are very soft unless they are hardened. For any
who doubt my claim, try placing a piece of piano wire across the capo
bar at the strut between the two top string sections and hitting the
wire towards the capo with a small hammer. The bar will be mangled
while the wire will be untouched. If the same test is carried out
with a hardened bar, the bar will be untouched while the wire will be
mangled.
The hardness of the cast iron is related to both its analysis and the
freeze time. Longer freeze-time plates such as V-pro plates, are very
soft. They also don't respond to hardening as well as conventional
sand cast plates. I seem to remember that V-pro plates typically have
a higher phosphorus content to make them pour better. If this is so
it may be the reason why they don't harden as well since phosphorus
is known to reduce the effect of flame hardening. If there are any
foundry men out there, they might like to comment on this.
I also did a custom job on a capo for a dealer here in Sydney in late
2006. The piano had a plate with a soft capo bar and a short
counterbearing length. There were problems with the tone of this
quite new piano despite the fact that the counterbearing length was
short, and I recommended that we shape and harden the bar. When I
attempted to harden the bar it wouldn't cooperate at all. So I ground
off the capo V, manufactured a new bar, hardened it and fitted it.
The result was most satisfactory. Here's an image of the bar shown
ready to be fitted to the piano. It is hardened and polished but not
plated.
If you can't see the image, a copy can be found at;
http://users.tpg.com.au/ronovers/ptr.custom.capo.jpg
The square-section bar in the image is the off-cut of the ground
stock from which the new bar was made.
There seem to be some who doubt whether a clean tone can be had from
a piano with hard bars. Below are links to full length tracks of an
Overs 225 with hardened capo's and hardened and detuned front duplex
bars. These mp3 files were converted from an audio CD at 192K, so the
sound is good with a freshly restarted computer using headphones or
decent speakers.
http://users.tpg.com.au/onyxer/Corelli.mp3
Scott Davie's recording of Rachmaninoff's Variations on a Theme of
Corelli, Op. 42
Piano: Overs 225 no. 3 - duration 18'38
Sydney jazz pianist and composer Mike Nock recorded a CD with his
trio on an Overs 225 piano. The following mp3 of Mike's composition,
Acceptance, can be heard at;
http://users.tpg.com.au/dotmewes/Acceptance.mp3
Piano: Overs 225 no. 3 - duration 7'04
The performers are; Mike Nock - piano, Brett Hirst - acoustic bass,
Toby Hall - drums.
Ron O.
--
OVERS PIANOS - SYDNEY
Grand Piano Manufacturers
_______________________
Web http://overspianos.com.au
mailto:ron at overspianos.com.au
_______________________
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