Quote: Originally posted by Luttgutt | I always thought that it makes small jumps (as small as the "teeth" on the wheel, if you know what I mean. I don't know the right terminology).
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No, it turns smoothly. The teeth of the gear do no more than provide the rotating screw surfaces which which to push the gear, and before one gear
tooth has been pushed out of range another has already come into contact with the screw, so that rotation is continuous, not incremental.
The worm-gear arrangement diverts the force of the string sideways against the screw, which means that, whereas the turning of the screw can
turn the gear that tightens the string, the opposite is not true, and the tension of the string cannot act to turn the screw. Therefore no friction
between the peg shaft and its bearing is necessary to maintain tension on the string, and so a mechanical tuner turns more easily, and more smoothly,
than a friction peg.
Even operating at its smoothest, a friction peg works by being "gripped" by the wood of the peg box, and thus prevented from being rotated by the
string tension, until sufficient force is exterted to overcome that friction, at which point the peg makes a tiny partial turn, after which its motion
is again checked by friction. So it is friction pegs which in fact operate by making numerous small incremental movements.
Finely adjusting anything with the human hand is always a problem of converting a large ("gross") movement into a small ("fine") one. With 18:1
mechanical tuners, twisting the finger grip one time around results in the string-bearing shaft making only 1/18 of a turn, a large motion being
converted into a smaller one, which naturally makes it easier to fine tune.
The larger the ratio, the greater capacity for fine tuning, though at some point the accuracy gained is beyond what is necessary, and the extra time
required to get a newly installed string up to tension becomes a nuisance itself.
David
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