[TowerTalk] Brake Winches

[Richard (Rick) Karlquist]

On 6/29/2015 1:08 PM, Roger (K8RI) on TT wrote:
> That's not correct!  It's the gear ratio! Not friction that makes the
> worm gear winch self braking!  I can raise my LM470 tower to vertical
> with one hand using my Dayton  worm gear winch.  With the double step
> down spur gear winch I could barely raise it with two hands.  It was

According to this reference:

http://www.machinerylubrication.com/Read/1080/worm-gears

"A second reason to use a worm gear is the inability to reverse the 
direction of power. Because of the friction between the worm and the 
wheel, it is virtually impossible for a wheel with force applied to it 
to start the worm moving."

The reference goes into a lot of detail about the many disadvantages
of worm gears, which was my original point:  they have their place
but are no panacea.

My Fulton KW3000 has a 50:1 ratio.  It requires about the same effort
going down as the previous Fulton KW2550 with only a 25:1 ratio.  Going 
up, the effort with the worm gear winch is double that of the spur
gear winch.  And the effort scales with the load, just like friction. 
We can argue whether it needs friction to work, but the fact of the 
matter is that it has a boatload of friction.  I measured the handle 
force with a torque wrench and it is over 60 foot pounds worst case.
I really wanted the safety aspect of a worm gear winch, so I replaced
the KW3000 with a motor driven 6000 pound winch with a 12 inch ring 
gear.  IMHO, both of these winches are only good for about half
their rated lift.

> A good worm gear winch has more friction than a spur gear winch, but
> turns "MUCH EASIER" than a spur gear winch for the same load.    I have

Again, that hasn't been my experience.  As always, YMMV.

Rick N6RK