[pianotech] Wire tensile limits

[David Love]

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