- Greeting`S' -
Chris Z asked a fine question regarding changes in gear ratio as the
number of threads on the worm is changed from one to four. The single
thread or helix meshed with a 24-tooth worm gear (wheel) gives a 24:1
ratio, speed cut by 24, torque on the worm wheel shaft multiplied by
24. The two thread worm and 24-tooth wheel (now with a different pitch
on the teeth) yields a 12:1 ratio, speed on wheel shaft divided by 12,
torque multiplied by 12. For three threads on the worm and a 24-tooth
wheel (still different pich), the ratio is 8:1. Four thread worm and
24 tooth wheel yields 6:1. So the biggest multiplier of torque is
gotten with the single thread worm. Due to a lot of sliding friction
between worm and worm wheel, the available torque may be only 90% of
that predicted by the ratio.
It is this friction which keeps the one and two thread worm and wheel
sets from allowing the drivers to be rotated except by rotating the
armature. Three thread sets are questionable. L used four thread worms
in the Pennsy turbine and the Berkshire so that the locomotive could
be pushed and have the drivers turn.
More than you wanted to know.
Cheer*S*
Rhett
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