[pianotech] New string broke twice

[Joe Goss]

Should one also order the pair so the partials will match?
Joe Goss BSMusEd MMusEd RPT
imatunr at srvinet.com
www.mothergoosetools.com
----- Original Message ----- 
From: "John Delacour" <JD at Pianomaker.co.uk>
To: <pianotech at ptg.org>
Sent: Tuesday, July 12, 2011 3:25 PM
Subject: Re: [pianotech] New string broke twice


> At 16:19 -0400 12/07/2011, Noah Frere wrote:
> 
>>...I'm thinking of ordering from a different company, being super 
>>careful while replacing, and seeing what happens. If it works 
>>normally, I could call Schaff and ask for a refund. If they refuse, 
>>no big deal.
> 
> Did you tell Schaff which note the string came from?  If not then 
> they had no alternative but to make the string to pattern, since they 
> lacked the data required to calculate whether the tension was too 
> high.
> 
>>FYI the strings that broke - and yes I mic'd them before installing 
>>- were .040 core; .118 winding; hitch to winding 5 1/8"; winding 
>>length 30 3/4".   The new string will be the same lengths but .039 
>>core and .116 winding.
> 
> So you have a core of 17.5 or 18 with the length of winding 77.1 cm. 
> Let's add 3 cm to get the speaking length (which is the only relevant 
> measurement) and we get 80 cm.
> 
> O.116" (your lower figure) is 2.95 mm.  The tension you require to 
> bring this string to pitch is 308 lbs. which is miles too high and 
> the string is bound to break.
> 
> Use a value of 19400 for K in the formula you find here:
> 
> <http://pianomaker.co.uk/technical/string_formulae/>
> 
> and work out what diameter you need the string to be, considering 
> that for mwg. 17.5 you should not exceed 70% or 300, ie. 210 lbs., 
> 220 lbs. for mwg. 18.
> 
> You will find that the proper overall diameter for the string is 
> 0.093" or less if you use a #17.5 core.
> 
> Do this every time you order an odd string and you will get no 
> breakages.  Otherwise you have nobody to blame but yourself.
> 
> JD
>