[pianotech] Breaking bass string

[Delwin D Fandrich]

Sorry, I should have been more specific. I was referring to the formula
(popularized by Al Sanderson) for deriving a safe tension limit for music
wire. Sanderson took this to be approximately 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. 

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. (The average is not necessarily the same as the
low plus the high divided by two but the average of the breaking point of
all of the samples tested.) By the above calculation the maximum safe
tension for this wire is 170.6 lbs. For modern music wire I think this is
overly conservative.

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


>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.

ddf


Delwin D Fandrich
Piano Design & Fabrication
6939 Foothill Court SW, Olympia, Washington 98512 USA
Phone  360.515.0119 — Cell  360.388.6525
del at fandrichpiano.com — ddfandrich at gmail.com


-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of John Delacour
Sent: Monday, April 11, 2011 11:04 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Breaking bass string

At 09:00 -0700 11/04/2011, Delwin D Fandrich wrote:

>It could also be that wire--generally--is tougher than it is given 
>credit for. The formula commonly used by scaling and/or rescaling 
>programs is one popularized by Al Sanderson and it is significantly 
>conservative. I'm not sure what wire specifications he based it on but 
>it gives a % of breaking strength that is considerably below that of 
>actual test with both Roslau and Mapes IG wire.

There is only one fundamental formula for calculating the _tension_ of a
string; it's not a question of opinion, and in my article at
<http://pianomaker.co.uk/technical/string_formulae/> I extract practical
methods from this one basic immutable formula.  If anyone reaches different
conclusions from the same data, then they are making a mistake somewhere
because the laws of nature do not change.

As to the strength of different gauge numbers of wire from various makers
there is no absolute law, of course.  The only certain way of determining
this is by repeated tests on a specially designed machine, such as those
used by Pleyel and Schiedmayer in the tests carried out on competing wires
in the second half of the 19th century.  Failing this we have to rely on the
tensile strengths claimed by the wire makers.

I have emphasized that the maximum of 70% **of the figures I gave in the
table I posted earlier** in this thread is the maximum that I use for bass
string manufacture using Röslau wire and I know from very long experience
that if this percentage is exceeded there is a very 
real likelihood of the string's breaking.     The evidence is 
presented to me weekly in the form of broken odd strings and broken strings
in sets that I am asked to replace.  My bass strings do not break, and they
also sound good.  In practice it is only for a small minority of pianos that
I need to reduce tension with respect to the original tensions and
experience seems to have taught hundreds of piano makers the same lessons as
it has taught me.

At 09:11 +0100 11/04/2011, I 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.

JD