String rollers.

[John Delacour]

At 22:23 05/10/01 +0000, Graeme Harvey wrote:

>..but the main query I had and I didn't
>allude to thoroughly enough was... is it possible to over-stretch wire?
>I know that newly strung pianos settle down after preparation and a number
>of tunings, but it is possible to stretch the wire further still and this
>can be demonstrated on old pianos, by simply pressing on a string and
>hearing the pitch go down.

The friction across the bridges (top and bottom) accounts for this.  If you 
were to pull to pitch a new Steinway string, for example, with a single 
clockwise turn of the tuning lever, you would end up with too much tension 
between the wrestpin and the agraffe and too little tension between the 
hitchpin and the bridge.  This can easily be verified if you choose a 
string with tuned partials at both ends; the partial near you will sound to 
high and the one beyond the bridge too low.  It is to even out the tension 
in the three lengths that we "set the pin", which is somewhat of a misnomer 
because this process does more than set just the pin.  In the case of a new 
string there is more work to do in the equalizing of the tension than in a 
piano that has simply dropped in pitch, but in either case it is necessary 
to pull up above pitch, let down to pitch and then pull up again very 
slightly to restore the tension in the nearest section and stabilize the pin.

I personally find that after a restring, with clean wire, new bearings and 
a clean bridge, practically all the setting of the tension can be done with 
the tuning lever, in spite of others' experience.  If course I do all the 
knocking down etc., including the tapping down of the strings on the 
bridge, for which I use a brass rod and a gentle hammer.  I also straighten 
all wire before installing and never use it straight from the coil.  When I 
come to the tuned partials, I do as much as possible with the lever and do 
a final evening out with the help of some pressure on the speaking length 
with a length of hardwood.  The knocking down also creates a shock that 
overcomes the static friction at the bridge-pins and causes the tension to 
level out.

I should say I don't do outside tuning, let alone concert tuning, and I 
always use tuners to finish the job, but I think I'm probably better than 
must tuners at setting up a piano to stay in tune, simply by dint of 
experience in this stage of the work.  I am no match for any good tuner 
when it comes to fine tuning.

>What happens to the partials and general overall sound characteristics of a
>string that has been over-stretched if this is indeed possible?

In brief, it breaks, now, today or next week.  Good piano wire is 'elastic' 
up to a certain tension; that is to say that as tension is increased it 
will get longer but when the tension is removed it will return to its 
original length, like an elastic band.  At a certain tension, the wire 
reaches its 'elastic limit' and becomes 'plastic', like plasticene or 
spaghetti, at the weakest point.  This happens over a very small range of 
tension and your wire is no longer piano wire but very hard plasticene.

The above definition of elasticity is what's taught at school.  When it 
comes to piano wire, it is not quite true, as I mentioned in another 
message a while ago, otherwise good pianos would only ever need one good 
tuning.  When you stretch a string, you are disturbing the internal 
equilibrium of the molecules.  They have, as all creatures aim to, found a 
place to be that is most comfortable.  You have wakened them up and they 
have to find a new comfortable position to settle down in, and this takes a 
long time since all their fellow molecules are doing just the same 
thing.  The end result of this is that all the molecules do finally go to 
sleep again and that internal tension is removed.  The pitch of the note 
therefore drops and the tone at the same time improves.  So far as I know, 
there is no book that adequately describes this whole phenomenon, let alone 
the improvement in tone.

JD