[TowerTalk] [Bulk] Re: Brake Winches

[Roger (K8RI) on TT]

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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