Breaking strengths / percents

[RicB]

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