[Delwin D Fandrich]

Michael,

58.7 mm (2.3125", or if you really insist, 2 5/16") is a bit long for C-88. This specification is a
much debated and one that is often misunderstood and inaccurately used. I've read some claims that
the speaking length of C-88 should never be any longer than 48 mm (about 1.875", or 1 7/8"). At the
same time, I've measured this length on several modern pianos and found it to be as long as 54 to
56 mm with few, if any, string breaking problems.

Please remember that the traditional formula used for measuring the percentage of breaking strength
is, at best, only a guide. At worst, it is quite misleading. The actual breaking strength of modern
#13 (0.031") music wire is about 290 to 300 pounds. So, instead of a string that is stretched to
85.4% of its breaking strength, what is really found in this piano is a string stretched to about
70% of its breaking strength.

Yes, the length of this unison is a bit long, and the tension is higher than I would normally like
to see it, but it's not impossibly high. If the wire is consistently breaking, your friend  might
consider changing coils of wire -- there are sometimes considerable variations in strength
characteristics from one coil to the next -- or perhaps even changing brands of wire. He might also
check the wire path. Is there a particularly sharp string deflection angle across the V-bar and/or
the counterbearing bar? Is there some other point of friction that might be a contributing factor
to string breakage? Is he inadvertently tuning the strings abnormally sharp?

Inaccuracies in the formula aside, it is true that changing wire sizes probably won't help all that
much. Changing the wire to #12 1/2 (0.030") would change the tension to 194 lbs. The average
breaking strength of #12 1/2 wire is about 280 lbs. resulting in a percentage of breaking strength
of about 69%. A slight improvement, but not much. Switching to #14 (0.033") wire would give 234
lbs. This wire has an average breaking strength of 325 lbs., giving a percentage of breaking
strength of 72%. Actually a bit worse.

In this case -- assuming that your friend isn't up to moving the bridge and/or the plate -- I'd
suggest the following:
    1)    Change to a #12 1/2 gauge wire at C-88 (and as far down as is consistent with good
scaling).
    2)    I'd suggest using Mapes International Gold wire. We've been using this wire for several
years with very good success.
    3)    I'd polish the string bearing surfaces to remove any roughness that might be causing
abnormal drag.
    4)    If there is any felt between the counterbearing bar and the tuning pin, I'd remove it.
    5)    I'd make sure that the strings do not bind against each other between the counterbearing
bar and the tuning pins.
    6)    I'd make sure I didn't cause any damage -- i.e., unnecessary bends and/or kinks -- to the
wire during stringing.

Regards,

Del



Michael J. Wathen wrote:

> Yesterday I got a call from a rebuilder who was dismayed and perplexed. He
> was ready to ship a piano out the door hoping to collect his earnings from
> a happy client. The problem was that everytime the tuner attempted to bring
> the last three or four notes up to pitch they broke.  After replacing the
> wire a few times they decided to change the guage but the strings kept
> breaking. The breakage occurred at the coil.
>
> note            gauge           hz              tension         %Br             Speaking length
> 88              0.031           4186            207.49                  85.41           2 5/16
> 87              0.031           3951            194.98                  80.26           2 3/8
> 86              0.031           3729            192.47                  79.23           2 1/2
> 85              0.031           3520            184.61                  75.99           2 19/32
> 84              0.031           3322            184.85                  76.09           2 3/4
> 83              0.031           3136            186.94                  76.95           2 15/16
> 82              0.031           2960            174.60                  71.87           3
> 81              0.031           2794            178.87                  73.63           3 7/32
> 80              0.031           2637            175.39                  72.20
> 79              0.031           2489            174.15                  71.68
>
> I did this on a spreadsheet and quickly changed the speaking lenghts to get
> everything around 72% of breaking point.
>
> Revised Chart
>
> note            gauge           hz              tension         %Br             Speaking Length
> 88              0.031           4186            175.21                  72.12           2 1/8
> 87              0.031           3951            175.00                  72.03           2 1/4
> 86              0.031           3729            178.27                  73.38           2 13/32
> 85              0.031           3520            175.75                  72.34           2 17/32
> 84              0.031           3322            176.61                  72.70           2 11/16
> 83              0.031           3136            176.13                  72.50           2 27/32
> 82              0.031           2960            174.60                  71.87           3
> 81              0.031           2794            178.87                  73.63
> 80              0.031           2637            175.39                  72.20
> 79              0.031           2489            174.15                  71.68
>
> Here is the question: why can't this problem be fixed by just changing the
> wires sizes?  Is it true that one cannot build a piano where the speaking
> length for note 88 is greater than 2 1/8?
>
> Michael J. Wathen                       For Information about Wapin click on URL below
> michael.wathen@uc.edu           http://ucccm56.ccm.uc.edu