[pianotech] Breaking bass string

[John Delacour]

At 11:29 -0700 10/04/2011, David Love wrote:


>Yes it has been gone over and I wish it were more clear to me the basis of
>decision making including the particular tonal aspects and blending
>disparate parts of the scale.  Thus, I try and avoid any real work in
>scaling other than an examination for my own interest.  Can you direct me to
>where to find published tables of breaking strains of piano wire.  I'm not
>able to locate them.

I gave you the link to Paulello's site in an earlier message in this 
thread.  His PDF tells the story pretty well.  His 'M' wire is 
roughly equivalent in strength to Röslau.  The values I use, so far a 
I remember, were from the old firm of Giese, since absorbed into 
Röslau.  It seems pretty odd to me that neither Röslau nor Mapes give 
any guidance at their websites.


>...it would appear by your standards that the maximum speaking 
>length at #88 would be something like 46 or 47 mm for #13 gauge and 
>I see this exceeded all the time both by accident and design without 
>adverse consequences...

I repeat, once again, that the 70% is the limit for *bass strings* 
which very rarely have a #13 core.  I see 50mm as a good compromise 
for note 88.  The old wire (especially Poehlmann over here) was 
phenomenally strong and some makers pushed their tensions to the 
limit relying on its strength.  The reason I became a stringmaker was 
that I couldn't get anyone to make me a set of strings for a 
Schiedmayer grand that would not break.  The top 5 singles had been 
replaced so many times that the frame was all chewed up and the 
7.75mm pins were still not holding the pitch.  Stringmakers just 
copied the old strings using the weaker modern wire and they broke 
before they came to pitch.  There are several famous makers who were 
almost as bad.


>  While this is outside the scope of the discussion on bass string 
>scaling I'd be interested in your comments.  Typically frictional 
>factors are said to potentially add about 15 - 20 lbs of tension 
>during the tuning process, still well within the safety margin even 
>at 52 mm it would seem.


Of course the effect of friction is one of the factors and there is 
also the fact that in chipping up, pitch-raising etc. the string 
needs to be pulled well above pitch.  The reason sensible people 
don't pull the high treble too high is precisely because the 
percentage strain is already close to the limit when the note is at 
pitch.   On many pianos you also have to be very careful with the top 
two or three singles and the highest bichords because these are too 
tight.

If you want to see how strong Poehlmann's wire became, read Dolge's 
book.  Wolfenden also calculated his scales on the basis of tensions 
that were possible with the older stronger wire.  In those days the 
market was huge and the competition between wire makers very fierce. 
I'd like to test the Chinese wire to see what tensions it will stand, 
but it's pretty awful stuff by the feel of it.

JD