Breaking strengths / percents

[RicB]

Hi Jurgen.

Yes, the readout on yeild point for Pure Sound would indeed be helpful. 
Combined with the figures for breaking point strength I can get a good 
idea just how he got his numbers. The problem seems to be that some 
tables seem to be operating with different definitions of breaking 
point, and some others seem to be using a generalized formula based on 
cross sectional strength of a wire.  One way or another these work out 
to a formula of the type a^x = b  where a is the diameter of the 
string.  I suppose its fine if they end up reasonably close to tables 
arrived at by measuring BP directly... but neither of the spreadsheet 
examples I have in hand line up close enough with Pure Sounds table.

Jason... the 57% bit was just what the formula Dave Roberts of the 
calculating technician gave.  Its probably a somewhat arbitrary figure 
<<just under 60%>>... a phrase one hears time and time again for 
recomendations for maximum tension for a string at pitch in scaling work.

Jurgen..  I tend to agree that where a verifiable table is available it 
is to be prefered to a formula. But then I'm just starting out on all 
this scaling stuff.  Still... strikes me that the comparisons I'm 
looking at here are too far apart for comfort.

If you could send me that table with yeild points on I'd be very greatful.

Cheers
RicB



    Jurgen writes:

    There seems to be different numbers floating about, that is for sure.  
    I am looking at a table of piano wire specs from an old Renner catalog
    which lists 1.5 mm wire (.0591") with a breaking strength of 360 kg =
    794 lb.  That is very close to what the Pure Sound website lists on its
    table at:   http://www.puresound-wire.com/otherwire.htm

    Apart from the data on that table, I have a hardcopy table which lists
    the yield point or limit of elasticity for Pure Sound.  Is that of any
    help?

        On Feb 1, 2007, at 9:31, RicB wrote:
         > 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.


    I don't think this kind of formula works for any kind of piano wire.  A
    thinner wire will always have a higher breaking strength per unit of
    surface area of the face of the wire.

         > 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 ?


    No doubt it does.  Apart from doing one's own testing, the best way to
    get reliable information is to go directly to or as close as possible
    to the source.  One can assume that Pure Sound's data on its own wire
    is correct.  Is there a spec sheet for wire published by Röslau or
    Mapes?

     >
     > Cheers
     > RicB

    Jurgen Goering
    Piano Forte Supply
    (250) 754-2440
    info at pianofortesupply.com
    http://www.pianofortesupply.com