[pianotech] Breaking bass string

[John Delacour]

At 09:43 -0700 12/04/2011, Delwin D Fandrich wrote:


>... 60% of the average breaking strength of the wire. This is the 
>same formula discussed earlier by David Love: T(limit) = 
>0.557d^1.667. I rather thought this was obvious from the context of 
>the discussion but apparently not.

I know of Sanderson's work in general, of course, but I have never 
come across his ideas on scaling and tensions.

>The breaking strength of wire as determined by test is generally given as a
>range and an average. For example, the breaking strength of Mapes IG No. 13
>gage wire (U.S., or 0.031"/0.787 mm) ranges from 290 lbs (low) to 302 lbs
>(high) and averages 296 lbs.

Well, since Paulello's figures (for his M(odern) wire are very close 
in practice to the figures I've used for 30 years for other German 
wire, let's compare them.  I take these figure from the document I 
mentioned before:
<http://stephenpaulello.com/pdf/PJ3-Wire-Paullello-prices-characteristics.pdf>.

As you will see, he uses the terms "Mechanical Resistance" and 
"Practical Breaking Load".  He also gives "Mechanical Resistance per 
mm2" and the table shows what is common knowledge, that the thinner 
the wire the stronger it is, owing to the effect of the 
drawing/patenting.


  For No. 13 wire (305/1000, 0.775 mm) Mechanical Resistance is given 
as 187 lbs and he takes 75% of that, namely 140 lbs. as the Practical 
Breaking Load.  As you see from the little table I posted the other 
day, the figure I arrived at 30 years ago (by a different route and 
for Röslau wire) is 137 lbs. so there is practically no difference 
between our ultimate max tension figure, and the same agreement 
continues, give or take a few pounds, right down the table.


>By the above calculation the maximum safe tension for this wire [No. 
>13] is 170.6 lbs. For modern music wire I think this is overly 
>conservative.

Well, for me 'modern wire' begins in 1867, in which year Poehlmann's 
No. 13 wire in independent tests (see Dolge) broke in Paris at 226 
lbs.  By the Chicago fair of 1893 their No. 13 broke at 325 lbs.  The 
strength of Poehlmann wire is beyond doubt.  The tensions used by 
some of the old makers took even the Poehlmann wire to the limit and 
the bass scales at least have so be severely modified to avoid 
"today's" wire breaking.  I speak of Röslau wire.  Certain makers, 
such as Schiedmayer had very high tensions also in the plain wire 
scale.

Although the figure you give for Mapes' wire are inferior to 
Poehlmann's 1893 values, they are significantly higher than the 
accepted values for Röslau wire, and this I find surprising.  I have 
complained before about the strength of Röslau in comparison with the 
old Poehlmann wire, but for a while there were other issues with 
their wire which now seem to have been resolved.

The fact remains that the maximum figures I give in my table have 
proved accurate in practice, and Paulello's figures simply give them 
further support.
As I have said, I know from experience the great strength of the old 
Poehlmann wire, which is far stronger after 100 years than new wire, 
so I have no reason to doubt that someone somewhere is able to 
produce wire that is as strong as Poehlmann was producing in 1890, 
and that someone may well be Mapes or Qiang Dong-Hai, who knows.  The 
fact is that for better or for worse practically everyone in Europe 
uses Röslau wire and Paolello's M wire seems to be roughly equivalent 
in strength.

So, presuming that your breaking strains for Mapes wire are reliable, 
then we are talking from two different worlds.

>Excluding the core wire of wrapped strings, in most pianos this is really an
>issue only through the top octave or so.

Yes and no.  Yes with regard to the risk of breaking but no with 
regard to the percentage of breaking strain if that is considered a 
factorof the quality of the tone.

>  Below that the working tensions are usually far enough below the 
>elastic limit of the wire that string breakage due to overly taut 
>strings is not an issue. (Except for the Sohmer 8' 4" grand which 
>had a tension of 296 lbs at C-64 on a #16 1/2 wire [0.038"/0.965 
>mm]. C-52, with #18 wire (0.041"/1.041 mm) had a tension of 276 lbs 
>and F-33, with #21 wire [0.047/1.194 mm] had a tension of 328 lbs.)

Well I can guarantee you could never string such a monster at all 
with Röslau wire.  Occasionally I do get odd breakages of Poehlmann 
wire for replacement and when I measure to check the tension simply 
can't believe that this string has lasted on a piano for 100 or 110 
years.  There were other good strong wires besides Poehlmann but I 
don't know how to name them.  Steinway I don't believe ever used 
Poehlmann wire.

>At 09:11 +0100 11/04/2011, you wrote:
>>>surely the only question worth asking is, do these pianos produce a
>>>better or a stronger sound in the high treble?
>
>>You didn't answer this question.
>
>No, I didn't. There is no easy "yes" or "no." As with most things 
>having to do with piano design this is interactive. Short speaking 
>lengths and small diameter wire--i.e., low tensions--work reasonably 
>well with thin soundboards and bridges that are relatively narrow 
>and not very tall. NY Steinways, for example, often have bridges 
>that are quite narrow and often just 24 to 28 mm in height at C-88. 
>There is not a lot of mass in these systems. When that gets 
>translated into one of the Asian languages, however, it often comes 
>out as thick soundboards and wider bridges that are in excess of 32 
>to 34 mm tall. Longer and higher-tensioned strings do work better in 
>these systems. Longer strings in the high tenor also allow placement 
>of the bridge a little further back, away from the treble soundboard 
>liner--usually a good thing.

Well I was talking only of the extreme treble and not of high-tension 
and low-tension scales in general, and I'll leave it at that because 
immediately at least three examples spring to mind of excellent 
sounding, vibrant pianos that have low tension scales and bridges 
taller, including much taller, than 34mm.  Admittedly they don't have 
half-inch mdf soundboards.

With regard to the breaking strain question, and the apparent huge 
difference in strength between Mapes' wire and the German stuff, I 
am, not for the first time, greatly intrigued.

JD