At 22:27 01/10/01 -0400, Bill Ballard wrote: >Thank you for that wonderful guided tour. I've always been curious about >that core wires tension during the winding. Is that an easy matter to set >quickly and reliably during the string winding? I have no idea how any >string winding could know what the tension of a given string on his the, >once this string is back in the piano and up to pitch. So there's probably >not reason to expect that any wire the winder might fasten to the lathe >would have its tension relative to eventual tensions in the finished >piano. I know why a wire in the lathe needs some tension. But how critical >are small amounts of tension when loading the core wire into the lathe. The funniest thing I have read on this topic comes from a certain German Meisterpianobuilder, who states that "...it is therefore necessary that the strings be subjected to the same tension and elongation on the string winding machine as when they are installed in the instrument." Thankfully he admits in the next paragraph that "I do not claim that the statements in this article are complete or even perfect". In fact the basis on which he founds this assertion is wholly illusory and illogical. The tension or "pull" applied to the copper covering depends, of course, on the gauge of the copper. When you are winding 0.15 mm copper, it is so slight and critical that the greatest concentration is required in order for the copper not to snap, whereas when you are spinning 2.05 mm. copper onto a No. 22 core, the pull is such as requires a good breakfast and a brave outlook (one of my apprentices called it 'hero copper'). In this case it is necessary to apply a very firm and even pull and not to accelerate the machine to fast for fear of twisting the swagings on the steel. In the first case, the steel wire will bow out only slightly towards the operative; in the second the angle will be considerable and it is to cater for the case of heavy copper that the machine tension needs to be set. On commercial German machines I have seen, the tension is achieved with a coil spring and applied by guesswork. In England some makers use pneumatic pressure. For the past 15 years I have used a simple dead weight which, ignoring friction, applies the same tension to all strings at all times and this tension is sufficient to keep the steel as straight as possible while the copper is trying to pull it outwards in a V. This weight is 80 lb., which is between 1/2 and 1/4 of the ultimate tension of the strings on the piano. So far as I know, not a single dud string has ever resulted from this practice and if, every six months or so, I have a string returned for rattling, then insufficient copper tension (tired man) or bad flattening (swaging) is the cause and never the machine tension. In a previous thread about string twisting, I mentioned residual tension in copper wire after it is spun on. In respect of machine tension, I would talk of radial compression of the (still slightly elastic) copper covering in the plane of the steel wire. There is enough elasticity in the copper to keep the spiral tight over a range of elongations of the steel. As the copper is wound on, with a slight backward angle tending to compress the coils or at the very least to exclude any possibility of gaps, a further stretching of the string of, say, 7 mm. will not result in gaps appearing. When the string is removed from the machine, the coils will be slightly compressed. When the strings are coiled for postage or transport, a further compression will be applied (and this can indeed be harmful). Within limits, the remaining elasticity in the coils will take up the slack and when the string is brought to tension on the piano, and thereby stretched say 1% of its dead length, no harm will come. It would certainly be worth while to make a thorough study of this question and it would be the height of arrogance in me to assume that my own practice could not be improved by such a study, which I intend one day to make, but I am sure that certain other aspects of the stringmaker's art are far more critical in the production of long-lasting, well-sounding covered strings than the machine tension, which should be sufficient to allow the easy achievement of the other critical goals and low enough to avoid any danger of breakages under the very rough treatment the steel receives during the covering process. JD
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