[pianotech] New string broke twice

[John Delacour]

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