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<DIV><FONT face=Arial size=2>Guys: I remember reading in the Piano Tone Building
book that pianos of that time was scaled to run about 160 to 180 lbs.tension on
the treble strings and about 200 lbs. on the bass strings. It was stated, also,
that the tensile strength on those strings was about 400 lbs above which they
would break. Any thoughts on this?</FONT></DIV>
<DIV><FONT face=Arial size=2>Gerald McCleskey.</FONT></DIV>
<BLOCKQUOTE dir=ltr
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=deanmay@pianorebuilders.com
href="mailto:deanmay@pianorebuilders.com">Dean May</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=pianotech@ptg.org
href="mailto:pianotech@ptg.org">'Pianotech List'</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, April 10, 2008 2:24
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: stretching wire</DIV>
<DIV><BR></DIV>
<DIV class=Section1>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I’ve done a little
more research and found some numbers. <o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">From Wikipedia: <A
href="http://en.wikipedia.org/wiki/Tensile_strength#cite_note-0">http://en.wikipedia.org/wiki/Tensile_strength#cite_note-0</A>
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><I><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-STYLE: italic; FONT-FAMILY: Arial">For
most metals yield point is not sharply defined. Below the yield strength all
deformation is recoverable, and the material will return to its initial shape
when the load is removed. For stresses above the yield point the deformation
is not recoverable, and the material will not return to its initial shape.
This unrecoverable deformation is known as plastic deformation. For many
applications plastic deformation is unacceptable, and the yield strength is
used as the design limitation.<o:p></o:p></SPAN></FONT></I></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">This substantially
concurs with what Mike says below, permanent stretch occurs when you pull the
tension above the yield point. It is, however, a little misleading when it
says “all” deformation is recoverable. <o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">I haven’t yet been
able to substantiate Mike’s claim that with modern piano wire the yield
strength is closer to the ultimate. I have found sources that place it at
43-35%. The Wiki article above is one and here is another: <A
href="http://www.mech.uwa.edu.au/DANotes/springs/fatigue/fatigue.html">http://www.mech.uwa.edu.au/DANotes/springs/fatigue/fatigue.html</A><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">This means if your
design tension is above 45% of breaking strength you will exceed the Yield
Strength, unless my sources are wrong. This is not really a problem as we are
still a long ways from breaking strength. <o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">It is important to
understand though that some plastic deformation does occur before Yield
Strength, though not really appreciable. If you’re really bored check out this
site: <A
href="http://books.google.com/books?id=dVQOAAAAYAAJ&pg=RA7-PA319#PRA7-PA335,M1">http://books.google.com/books?id=dVQOAAAAYAAJ&pg=RA7-PA319#PRA7-PA335,M1</A><o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Scroll down to page
336, for example. You will find a strain table for 17 gauge wire. At 100 lbs
tension the wire elongated .0122 inches. When they took the 100 lbs off it had
a permanent set (i.e., plastic deformation) of .0002 inches. When they got up
to 300 lbs the permanent set was .0047 inches. At 422 lbs the wire sample
broke (ultimate strength). <o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial">Mike, do you have a
reference we can look at that says differently? The reference above was
printed in 1918 and perhaps “modern” piano wire would be different.
<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
style="FONT-SIZE: 10pt; COLOR: navy; FONT-FAMILY: Arial"><o:p> </o:p></SPAN></FONT></P>
<DIV>
<P class=MsoAutoSig><B><FONT face="Bradley Hand ITC" color=navy size=6><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 22pt; COLOR: navy; FONT-FAMILY: 'Bradley Hand ITC'">Dean</SPAN></FONT></B><FONT
color=navy><SPAN style="COLOR: navy"><o:p></o:p></SPAN></FONT></P>
<P class=MsoAutoSig style="MARGIN: 0in 0in 0pt"><U1:PERSONNAME
u2:st="on"><st1:PersonName w:st="on"><FONT face="Times New Roman" color=navy
size=3><SPAN style="FONT-SIZE: 12pt; COLOR: navy">Dean
May</U1:PERSONNAME></SPAN></FONT></st1:PersonName><FONT color=navy><SPAN
style="COLOR: navy">
cell 812.239.3359 <o:p></o:p></SPAN></FONT></P>
<P class=MsoAutoSig style="MARGIN: 0in 0in 0pt"><FONT face="Times New Roman"
color=navy size=3><SPAN
style="FONT-SIZE: 12pt; COLOR: navy">PianoRebuilders.com
812.235.5272 <o:p></o:p></SPAN></FONT></P>
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u4:st="on">Terre Haute</SPAN></FONT></st1:City><FONT color=navy><SPAN
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<P class=MsoNormal><FONT face=Arial color=navy size=2><SPAN
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<P class=MsoNormal><B><FONT face=Tahoma size=2><SPAN
style="FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Tahoma">From:</SPAN></FONT></B><FONT
face=Tahoma size=2><SPAN style="FONT-SIZE: 10pt; FONT-FAMILY: Tahoma">
pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] <B><SPAN
style="FONT-WEIGHT: bold">On Behalf Of </SPAN></B>Mike Imbler<BR><B><SPAN
style="FONT-WEIGHT: bold">Sent:</SPAN></B> Wednesday, April 09, 2008 7:01
PM<BR><B><SPAN style="FONT-WEIGHT: bold">To:</SPAN></B>
pianotech@ptg.org<BR><B><SPAN style="FONT-WEIGHT: bold">Subject:</SPAN></B>
re: stretching wire</SPAN></FONT><o:p></o:p></P></DIV>
<P class=MsoNormal><FONT face="Times New Roman" size=3><SPAN
style="FONT-SIZE: 12pt"><o:p> </o:p></SPAN></FONT></P>
<DIV>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">As a mechanical engineer, I concur
with Ron. John's cite of the high tension electrical wires makes it
clear that they are being tensioned beyond yield strength, which is why the
article suggests heat treating the wire (which increases yield
strength). Yield strength is the point where the wire would plastically
deform (stretch) which is less than ultimate strength (breaking stress).
Therefore, you -could- stretch piano wire, but you would be pulling it above
its yield strength. This would be more likely with more
ductile wire which has a yield strength appreciably lower than
ultimate. With a more modern piano wire, yield strength is closer to
ultimate.</SPAN></FONT><o:p></o:p></P></DIV>
<DIV>
<P class=MsoNormal><FONT face=Arial size=2><SPAN
style="FONT-SIZE: 10pt; FONT-FAMILY: Arial">
Mike</SPAN></FONT> <o:p></o:p></P></DIV></DIV></BLOCKQUOTE></BODY></HTML>