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 >
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