[pianotech] Wire tensile limits

[Dale Erwin]

JD
  Thanks to your voice of experience

 

 

Dale S. Erwin
www.Erwinspiano.com
Sitka Soundboard Sales
Ronsen Piano hammers
209-577-8397




 

 

-----Original Message-----
From: David Love <davidlovepianos at comcast.net>
To: pianotech at ptg.org
Sent: Fri, Apr 15, 2011 7:30 pm
Subject: Re: [pianotech] Wire tensile limits


Thanks for clarifying all that.  Helpful.  



David Love

www.davidlovepianos.com





-----Original Message-----

From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf

Of John Delacour

Sent: Thursday, April 14, 2011 1:05 PM

To: pianotech at ptg.org

Subject: Re: [pianotech] Wire tensile limits



[ subject was 'Breaking bass string' ]





Looks as if there was a problem with the image.  Here it is again as an

attachment.







At 10:28 +0100 14/04/2011, I wrote:



>OK, I've worked it out now and applied it to the published Ršslau 

>breaking strains...



The chart below compares the curves of (1. blue) 80% of 'practical 

breaking load' calculated from Ršslau official figures and (2. red) 

the tension calculated with the formula T = 0.515 (dthou^1.667), 

which gives 60% of the 'ultimate tensile strength' = 'nominal 

breaking load' = 'mechanical resistance'.



The scale goes from 10 mwg to 26 mwg including half sizes. I have 

inserted the American size 13 at column 6. As you see, the values are 

almost coincident except for the very thick sizes, where it really 

doesn't matter.





I reiterate that this gives the absolute maximum at which point the 

wire reaches its elastic limit.  The values in question are:



13: 151 lbs.

13 American: 156 lbs.

15: 188 lbs.

17: 225 lbs.

19: 267 lbs.

20: 287 lbs.

21: 308 lbs.



The maximum allowable for bass strings, using Ršslau wire, I have 

learned from long experience, is 55% of ultimate tensile strength and 

I never exceed this.  In practice I use nearer 50% of UTS (60% of 

'practical breaking load') for many serious pianos.  It is only 

necessary to approach the elastic limit in certain very short pianos. 

Examination of hundreds of 19th and 20th century pianos shows that 

the great majority of them obey the same rule, some of them very 

closely.



JD






 
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