Having used winches and worm gear/worm gear wheels in industry, and in
ham radio for over 50 years I can only go by experience which shows far
less effort to raise a given load using a good worm gear winch. Yes,
the worm gear has far more contact area between the worm gear driver and
the worm gear wheel which would reduce the efficiency. I have not seen
any really good worm gear to worm gear wheels used in the ham world for
raising towers including my Dayton. Although it certainly makes raising
the 1300# LM470 far easier. The winch sees a far greater load than the
1300#, but I've not measured the dimensions, or angle to calculate the
loads. It's just a 50:1 worm gear is far easier to use raising that
1800# tower compared to a 15 or 20:1 spur gear.
A good worm gear to worm gear wheel has a finely machined and/or lapped
interface that is polished. The area of contact is sliding as it is in
spur gears, but that area is far greater in the worm gear to worm gear
wheel and 90 degrees to the movement of the driven gear. Compare a
precision worm gear to worm gear wheel (polished steel worm gear to
brass worm gear wheel) to those in the winches we use Stamped steel
on steel with a minimum of machining. Without going into the
manufacturing steps, the stamped gears are much less expensive to make.
I disagree with two points in the article. You can reverse direction on
a loaded worm gear/worm gear wheel and a high viscosity grease is no
longer needed to lubricate the gear interfaces. Greases like BR2 are
very slippery and of a viscosity used in standard grease guns like
Alemite . It's not clear, but he may be referring to the self breaking
action, but depending on load, the worm gear can run under load in
either direction. The friction varies greatly depending on the size of
the gears and the load applied. Large gears with heavy loads do indeed
have substantial friction.
"Used to be"(I worked in maintenance for 26 years before earning a
degree in CS), we used a black, thick, and gooey grease affectionately
known as bear grease, or "similar" names. Get a little on your hands and
you'd look like you had bathed in it by the time you got back to the
shop and it was very difficult to wash off. We used it on small worm
gears and 45 degree beveled gears. Mainly it was used (in our operation)
to prevent vibration, or mechanical resonance in sensitive areas.
Other than the vibration issue, we switched to the BR2 grease for
reduced friction.
One shortcoming of the stamped, steel on steel gears, is they are often
assembled with excess pressure between the worm gear and worm gear wheel
and depend on the gears "wearing in". Winches using this approach can
require a lot of effort to use with a notable reduction in effort over
the first few hours of use. (hours of use on a winch?)
In a more crude gear system, like the winches which use steel on steel
rather than steel on brass, where they depend on wear to get the proper
mating surfaces I'd like to try the proper mating of the gear
interfaces. If I had the time, money, and two working hands, I'd like
to try lapping the crude gears with ever finer grades of lapping
compounds until they give a proper, smooth, interface and use a good
grease meant for a high pressure mating surface as in these winches.
Lapping gears has a steep learning curve with a fine line between too
much and too little.
One change I'd make would be to add zerks to the worm gear bearings so
they could be properly lubricated.
Mating surface match, mating area, smoothness, and lubrication are
crucial to the proper operation of the worm gear and worm gear wheel
with minimum drag.
Quoting the article's conclusion:
"In Conclusion: Although a worm gear will always have a few
complications compared to a standard gear set, it can easily be an
effective and reliable piece of equipment. With a little *attention to
setup and lubricant selection,* worm gears can provide reliable service
as well as any other type of gear set." (bold is my change)
73
Roger (K8RI)
On 6/29/2015 5:10 PM, Richard (Rick) Karlquist wrote:
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
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
--
73
Roger (K8RI)
---
This email has been checked for viruses by Avast antivirus software.
http://www.avast.com
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|