Capo-hardening

[Ron Overs]

Roger wrote:

>. . . . . I am either mis reading you, or dis agreeing?   Having 
>spent time in the Yamaha foundry.  The V Pro plate is cooled and 
>ready to work in 40mins flat.

This is interesting, and contrary to what we were told at the time 
(1977 I think) of the release of the V pro Yamaha plates.

>The sand cast plate is left in the mold with electrical heating for 
>24hrs approx.  The slow cooling gives the stress relief required to 
>prevent distortion.   The rate of cooling also effects the structure 
>of the free carbon crystals.

The idea of electrically heating and slowing the freeze time would 
certainly do what you claim. Is this how Yamaha produce their CF 
plates?

>I have heard stories about aging plates, out side in the elements 
>for extended periods, for further stress relief.   This may be sales 
>smoke and mirrors.

This was practiced regularly in the days of Wolfenden. However, in 
Wolfenden's day moulding sand contained some residual moisture at the 
time of the pour. Therefore, freeze times were very short and plate 
failures were relatively common (of course these plates had harder 
bars which were less prone to noise). Today, moulding sand is typical 
held together with synthetic binders (ie. two pack type compounds). 
This of course, allows for slower freeze times and softer bars.

>The water in the sand, quenches the melt on contact, and case 
>hardens the material to a depth of about 1mm.   So the skin of a 
>sand cast plate is much harder.

Historically, certainly.

>It's the addatives in V Pro that enables the material to be cooled 
>this rapidly.  Unless you know the composition, there is no way to 
>look up Brinell or Rockwell hardness tables to verify this.

And then even if you know the analysis, any freeze time variation 
will also affect hardness.

>   My gut feel is that the skin of sand cast is much harder, but if 
>over grinding has taken place, to bite into the raw grey iron, then 
>the reverse may be true.

Agreed, in general the sand cast plates do have harder bars - but 
even they are relatively soft when compared to a hardened bar, even 
when the 'skin' is retained. In my experience V plates always have 
very soft bars but they do respond to hardening, though not quite as 
effectively as the sand cast plates.

Some sand castings are deliberately cooled to reduce the freeze time, 
increasing the surface hardness.

Clearly Roger, there would seem to be some disagreement between us. I 
look forward to further clarification. I would hasten to add here 
that I have had limited foundry experience. The information I have 
has come from piano factory representatives and engineering hand 
books, so the information may not have been totally reliable. Anyone 
else wish to add to this thread?

I will be investigating these matters further, since I am presently 
designing our new 230 cm grand plate. When further information comes 
to hand I will inform the list.

Richard, saw your post on this topic earlier today when I arrived at 
the workshop. You questioned the string service life one might expect 
from hard bars. We have been reshaping and hardening capo and duplex 
bars since 1995. We have found that the strings survive very well 
provided that good tuning hammer technique is used. One of the 
commercial instruments we rebuilt previously was being tuned by 
another technician in addition to ourselves. This tech' had a most 
ordinary tuning technique, pulling the wire 'all over the shop' 
(which was also very unsettling for the tuning stability - it would 
take a couple of tunings to get the piano back into tuning stability 
once this 'technician' had done his thing). This piano started 
breaking wire after just one year in service. However, pianos which 
we alone have been servicing typically see at least five years of 
service before the first wire breaks. For high use commercial pianos, 
I would regard this as satisfactory.

Best regards,

Ron O
-- 
Overs Pianos
Sydney Australia
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Web site: http://www.overspianos.com.au
Email:     mailto:ron@overspianos.com.au
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