Capo-hardening

[Richard Brekne]

Roger... somehow I didnt get this posting of yours... somebody want to
send this along in full. I would be greatly apreciative...

Ron Overs wrote:

> 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.

That is my understanding as well... in fact one of the big "plusses" is
the speed thingy...

> 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.

Yes..

> 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.

I understand, tho I am very far from sure, that Petrof forces a very long
cool time for their plates. I am told... tho I have no idea whether its
trur or not... that they still employ so called "plate tuners" and that
this whole plate making philosphy is one of the reasons that Petrofs have
the sound that they do. I have been trying to find information to confirm
or deny any of this kind of thing for about a year and a half now with
little success... information about all this seems to be hard to come by.

>
> 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.

I have heard this many times as well. I have also heard many times that
it is only the skin which is harder in sandcast plates.

>
> 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.

This is my understanding of things. In fact the only place I have ever
heard anything different is from Ron O. And of course that has me
scratching my head trying to figure out whats what.

>
> 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.

Again... everywhere else I turn seems to point at the V-pro capo bar
surface is much harder then the average sand cast counterpart.
Shheeeshhh you'd think a simple fact like this could be easily documented
and put to rest once and for all...grin..

>
>
> 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.

Interesting....

>
> Best regards,
>
> Ron O
>

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no