stretching wire

[Dean May]

  _____  

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of William R. Monroe
Sent: Thursday, April 10, 2008 10:41 AM
To: Pianotech List
Subject: Re: stretching wire

 

I don't think this degree of plastic deformation stands in the way of the
"strings don't stretch over the long term" idea.  First, keep in mind the
amount of stretch cited here.  Even at the 300 pound tension, the plastic
deformation was given as about 5 thousandths of an inch.  Maybe significant
in some way, but it sure wouldn't account for any "winding up of wire on the
tuning pin."  

 

 

 

Agreed. The sample wire size was 6" long so for a 30" wire your .005" would
end up as .025". But we are talking pretty small movements of the tuning
pin. 

 

Dean

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I don't know the pitch change for an increase in wire length of 5 thou for
17 ga wire, but maybe our scaling guys can tell us.  I would enjoy knowing.

 

More to the point, when did this plastic deformation occur, i.e., how long
was the wire left tensioned?  I tried wading through this study, but didn't
find the methods outlined very well.  It appears the wires were only
tensioned for a short period (less than a day).  In other words, this
plastic deformation of music wire occurred as the wire was initially brought
to tension, and stayed there for the duration.  It does not conclude that
the wire continued to deform over any length of time.

 

 

So, for our purposes, this study seems to suggest that as we chip or raise
pitch, there is bound to be some plastic deformation, but that once
tensioned, no more deformation occurs over the long-term.  So, the theory
that strings stretch over the long-term does not seem to be supported by
this study/information.

 

William R. Monroe

 

 

SNIP

 

 

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: http://books.google.com/books?id=dVQOAAAAYAAJ
<http://books.google.com/books?id=dVQOAAAAYAAJ&pg=RA7-PA319#PRA7-PA335,M1>
&pg=RA7-PA319#PRA7-PA335,M1

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). 

 

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. 

 

 

Dean

Dean May             cell 812.239.3359 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/pianotech.php/attachments/20080410/2e03041d/attachment.html