Yup!
73
Roger (K8RI)
On 6/29/2015 6:51 PM, Grant Saviers wrote:
Not all worm gears are self-locking. Wikipedia:
"...Worm gear configurations in which the gear cannot drive the worm
are said to be /self-locking/. Whether a worm and gear will be
self-locking depends on the lead angle, the pressure angle, and the
coefficient of friction; however, it is approximately correct to say
that a worm and gear will be self-locking if the tangent of the lead
angle is less than the coefficient of friction.
and
Occasionally a worm gear is designed to be run in reverse, resulting
in the output shaft turning much faster than the input. Examples of
this may be seen in some hand-cranked centrifuges or the wind
governor in a music box...."
So with a large enough lead angle and/or good enough lubrication (e.g.
TFE loaded grease) a worm drive winch might provide a nasty surprise.
Check the specifications.
I think the high friction source in many inexpensive worm gear winches
is the shaft bearings (particularly the thrust bearing on the worm)
being bronze rather than a ball bearing. Many speed reducers use worm
drives and ball bearings on the shafts and have reasonable friction.
Grant KZ1W
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