Counterbearing angle

[Delwin D Fandrich]

----- Original Message -----
From: "Overs Pianos" <sec@overspianos.com.au>
To: <pianotech@ptg.org>
Sent: March 16, 2001 10:43 PM
Subject: Re: Counterbearing angle



Sorry to come back to an issue this long after it has come and gone on the
list, but a couple of items in this one have bothered me ever since reading
them:

>
> >My questions are:  Is there an optimum amount of counterbearing?
>
> Yes.
> -----------------------------------------------------------

No. There is no optimum amount of counterbearing or, more properly, string
deflection angle. The optimum string deflection angle is a function of the
duplex length and the frequency of the speaking length. Mostly duplex
length.

In general, shorter duplex lengths do not require as great a string
deflection angle to effectively and efficiently cut off the speaking length.
Longer duplex lengths require greater string deflection angles to
effectively cut off the speaking length. It is these longer duplex lengths
that cause trouble. They invite the transfer of energy from the speaking
length of the string into the duplex length. Once there, this energy causes
no end of problems and generates no end of exotic solutions to quiet it
down. I prefer to keep it out by efficiently terminating the string at the
V-bar.



> >Is there a recommended way of building it up in the capo section
> >when dealing with a cast duplex as in a Steinway?
>
> We have done it, but its far too long a job. Better to cut off the
> bars with an angle grinder and put them where they should have been
> placed at the time of manufacture.

Ditto.

We both shorten the duplex string length and increase the string deflection
angle by replacing the counterbearing bars.

But we have not found it necessary to harden all of these various parts --
certainly not the counterbearing bars. If the back counterbearing bar is
reasonably close to the right place and is reasonably close to the right
height, i.e., keeping the duplex reasonably short and the string deflection
angle reasonably high, the hardness of the material does not seem to matter
all that much. For the counterbearing bars we simply use either half-round
or half-oval extruded brass. Usually half-oval.

If hardness is an issue with a particular piano it will be at the string
termination and my solution of choice is to grind off the V-bar and replace
it with a silicon bronze casting. The patterns are not particularly
difficult to make, the castings are not all that expensive and they can
easily be placed to correct for wandering strike points. They are easily
shaped if needed and -- depending on the exact alloy -- can approach the
hardness of mild steel while retaining the lubricity of brass.

I have designed these into several new pianos, though I don't know of any
that are still using them -- the manufacturers seem to prefer struggling
with improperly shaped and placed (but traditional) V-bars cast with the
plate. Or, more frequently, they seem to prefer simply ignoring the myriad
problems associated with improperly shaped and placed cast-in V-bars. And,
of course, they do cost a bit more and they do introduce an additional step
in the plate preparation process. What do you expect for $25,000 to $50,000?
Clear, clean trebles? Don't be silly!




> >What are the downsides to building up the counterbearing, if any?
>
> Time to do the job. Greater risk of string fatigue and breakage.

Yes, and it's that second one that bothers me about the practice of
hardening things around string deflection points. Especially at the V-bar.
Every company I'm aware of that has produced pianos with hardened V-bars has
come to regret the practice, though not all have admitted so. The warranty
costs of replacing all those broken strings can be considerable.

We harden string termination points in practice (either the V-bar or the
counterbearing bar), though I've done a reasonable amount of experimental
work with it. I've just not found it to be either essential or advantageous
if the string deflection angles are in the ball park and the duplex length
is properly short enough.

Again, I've more to say on the subject, but most of it has already been
written. Check the back issues of the Journal.

Regards to all, I'm out of here -- see you in a few days.

Del