Breaking strengths / percents

[Jason Kanter]

55.7% seems ridiculously precise. Isn't the notion of "maximum safe tension"
more analogous to e.g. the speed limit of 55 miles per hour? Where in fact
there are so many variables in the car, the driver, the shape of the road,
surface conditions, traffic conditions and environmental variables.

Granted, well-manufactured wire may be highly consistent on the spool, but
as soon as it is strung, bent, twisted, stretched with different tension in
different segments of its length, and possibly kinked or nicked, how precise
can we really be?

Jason

On 2/1/07, RicB <ricb at pianostemmer.no> wrote:
>
> Thanks Jurgen.
>
> Pure sound supplies a table of breaking strengths for both Pure sound
> and standard piano wire, along with a few others from Malcom Rose.  I'm
> just trying to back engineer a bit of some of these formulas tossed
> around in publications so as to ascertain exactly what these were saying.
>
> For example... in the Calculating Technician the maximum safe tension
> for standard wire is 0.557*d^1.667  (d is diameter in mils). If you have
> a 1.5 mm Ø wire (circa 59 mils) you get  0.557*897 lbs = 498 lbs maximum
> safe.
>
> Now... this looks to me like 897 lbs is the breaking strength used
> here... and 55.7% of that is figured as maximum safe..  If that is so
> then  we have 406 kg breaking strength for modern wire according to this
> formula.  But looking at Pure Sounds table for breaking strength of
> modern wire he has 370 kilograms.  Thats quite a difference really.  If
> thats not enough confusion... Delecour handed out a lookup table for a
> spreadsheet a while back which has this same 1.5 wire (59 mils) at 276
> kilos.
>
> I suppose I could just contrive a formula from any given data set like
> Pure Sounds page. For example if you take a 1 mm (39.37 mils) and figure
> the exponent needed for 39.37 mils to arrive at the 369.5 lbs that Pure
> sound gives you simply take   x = ln369.5 / ln39.37 , which is
> 1.609622688.  But then if you use that for the rest of the table it
> doesnt add up.  So the breaking strengths that Pure Sound gives can not
> be figured by this kind of formula... ie.  a^x = b.
>
> Point is that if you are anywhere near maximum breaking strengths given
> by one table for one type of wire... you may very well be well over the
> limit on somebody elses table.  Kinda makes depending on the
> calculations of spreadsheets a bit iffy until you have reliable figures
> yes ?
>
> Cheers
> RicB
>
>
>     Ric-
>     I don't have a formula, but I do have a table with all the breaking
>     strengths of Pure Sound Wire from # 7 through # 25.  Would that be
>     helpful?  What sizes are you working with?
>
>     Jurgen Goering
>     Piano Forte Supply
>     (250) 754-2440
>     info at pianofortesupply.com
>     http://www.pianofortesupply.com
>
>


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