Counterbearing angle

[David Love]

Ron:

Thanks for all the input.  I have often wondered at the consistency in 
agraffe manufacturing because I have had periodic problems with new 
agraffes.  Yeah, I just threw out brass without really thinking about it but 
why, then, would agraffes be made from brass especially when the inside of 
the string hole is subject to rapid wear?  I am interested in hearing more 
about your duplex modifications using carbon steel and formulas for 
repositioning.  Will you be publishing something after Reno?

David Love


>From: Overs Pianos <sec@overspianos.com.au>
>Reply-To: pianotech@ptg.org
>To: pianotech@ptg.org
>Subject: Re: Counterbearing angle
>Date: Sat, 17 Mar 2001 17:43:37 +1100
>
>David, Paul and list,
>
>David wrote;
>
>>I've often run into problems on Steinways with buzzing through the
>>agraffes (even new ones) in different places in the piano.
>
>That's because even the new agraffes (even from S&S) are often poorly
>shaped (cut some new ones in half through the string hole, and
>examine the hole profile with a light and a magnifying glass - you
>will see what I'm referring to), with parallel mid sections through
>the string hole. We've had similar experiences with new agrafffes,
>and when replacing or retaining the existing agraffes, they all get
>reshaped with a specially profiled cutter.
>
>>Most recently on a D this problem occurred in several places in the
>>tenor and just below the bass break (not a string winding buzz). I
>>have also run into problems with clean intonation on note 53 (last
>>agraffe)
>
>Very often the string approach angle is not uniform throughout the
>string section, and often the approach angle is steeper at the
>section ends where the understring felt or bearing bar runs up the
>fillet radius in plate casting. The steeper angle will cause the
>cutting action of the string during tuning, to damage the string hole
>more quickly than for the other notes in the string section.
>Therefore it is more common to get noisy agraffes towards the ends of
>string sections.
>
>>and leakage throught the capo section is a constant battle.  I have
>>in the past remedied problems in the agraffe section by increasing
>>the counterbearing angle by adding a brass semi round between the
>>tuning pin and the agraffe.
>
>But brass itself is quite soft and prone to grooving, also becoming
>noisy in a very short time.
>
>>. . .  In the capo section sometimes the problem is the shaping of
>>the v-bar itself which can be remedied.
>
>Sure. But the bars themselves are so soft that they quickly groove
>again and get noisy (even the phosphor bronze variety). Although some
>of them will be noisy to start with, since the practice of attempting
>to tune the duplexes to a harmonic of the speaking length (as Yamaha
>and Steinway do) is asking for noise.
>
>>But again, I have often wondered whether or not the tone/power might
>>not be improved by building up the cast duplex.  A hollowed out
>>half-round of brass could be fitted over the cast duplex, or if the
>>duplex needs to be detuned
>
>But it's too soft.
>
>>,it could be placed in a different position.
>
>Now you're onto something. But its the bar which should be
>repositioned, and it should be hard enough to avoid string
>deformation.
>
>>My questions are:  Is there an optimum amount of counterbearing?
>
>Yes.
>
>>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. We had to make a new duplex bar
>for a D in 1994. The original bar obviously didn't form when the
>plate was cast. A welder was apparently engaged to build up a duplex
>bar. When we rebuilt the piano in 1994, the duplex bar would not
>harden (because pure nickel won't will it). So we had to make a new
>bar. I couldn't encourage any of the professional welders in Sydney
>to take on the job. So after much experimenting on samples I learned
>to do it myself. I've only done it once, and have no wish to do it
>again. In any case, we now cut off the duplex bars of Steinways and
>put in our own hardened carbon steel bars (which are profiled, height
>adjusted and nickel plated to prevent corrosion). These are
>positioned according to our own formula for length and approach angle.
>
>>What are the downsides to building up the counterbearing, if any?
>
>Time to do the job. Greater risk of string fatigue and breakage.
>
>There are four variables which need to be considered in a wholistic
>manner when considering the front duplex system.
>
>* Duplex length (longer is noisier, in-tune is noisy)
>
>* String approach angle (higher means more string breakage - lower
>means more energy bleed across the capo, but if the duplex isn't
>tuned and it's short, all's OK)
>
>* Bearing hardness (harder and smaller radius requires a lower string
>approach angle)
>
>* Bearing bar radius (larger is noisier, but the wire lasts longer -
>smaller is cleaner but the wire will fatigue earlier.
>
>
>We use 0.5 - 0.75 mm radius, very hard and polished, with a string
>approach angle of 12 - 15 degrees. We have a special formula for
>calculating the duplex length. Which we will pass on to all after we
>exhibit our Overs-Steinbach 225 cm grand piano at Reno this July.
>
>For a look at a detuned, shaped and hardened set of the original
>duplex bars on a Yamaha G2 (just finished) visit;
>
>http://www.overspianos.com.au/g2fdp.html
>
>Regards to all,
>
>Ron O
>
>--
>
>_________________________
>
>Website:  http://www.overspianos.com.au
>Email:      mailto:ron@overspianos.com.au
>_________________________

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