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Re: [TowerTalk] [Bulk] Re: Brake Winches

To: Grant Saviers <grants2@pacbell.net>, "Richard (Rick) Karlquist" <richard@karlquist.com>, towertalk@contesting.com
Subject: Re: [TowerTalk] [Bulk] Re: Brake Winches
From: "Roger (K8RI) on TT" <K8RI-on-TowerTalk@tm.net>
Date: Tue, 30 Jun 2015 04:19:17 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
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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