[TowerTalk] US Tower seized gearbox

[Roger (K8RI) on TT]

*Notice: I make no claim for the safety for the operations below. 
Proceed at your own risk!*

I'm doing this at 4:00 AM so please excuse any typos and go for what I 
meant, rather than what I said If you can figure it out..

My limited experience with tower pulleys is the ones I have used would 
only increase the force a bit if they froze, but the cable would still 
slide through.  If they really grabbed the cable, the motor would run in 
the down direction and the up cable would go slack. A jammed, caught, or 
pinched pull down cable would hang in both directions, but should allow 
a bit of motor run, if only for a turn or two of the motor shaft.   
Limit switches can often create these problems IF they are the double 
pole type that allows the motor to run in the opposite direction.  IE 
down off the up limit and up off the down limit.

Gear boxes, I have had a lot of experience with these, but it was many 
years ago.

A frozen gearbox, or motor would result in no turning.  IF, the AC motor 
uses a starting capacitor, that would seem to be a starting place.  As 
others have said, check the gear lube for quantity and quality.  
(discolored, metal filings, or a gritty feel) Any of those call for a 
complete flushing of the gear box which can be difficult, in some 
instances, with it bolted down.  If any of the bearings, or bushings 
have failed the soaking in WD40, or most and good penetrant "might" free 
it up.(already suggested)  Rough or frozen ball bearings need to be 
replaced. Sealed bearings are very reliable, but the do fail on occasion 
for various reasons. The less expensive gear boxes use bushings on the 
slow moving output shaft.  Some also use them on the input shaft. Some 
highly rated and somewhat expensive cable winches use all bushings where 
bearings are required. The rational is probably the low speed and heavy 
load are better handled with Oillite or (oil-lite) bushings, or 
expensive bearings.

The following is a generic approach to troubleshooting the assembly.  My 
apologies if this has been covered as I've read most, but not all posts 
in the thread.

It would be wise to block the tower sections if it can be done safely 
and *WITHOUT* climbing the tower.  Never put your hands inside of a 
malfunctioning, crank-up tower without first blocking the tower 
sections! Use a ladder, or borrow one that will get you high enough. 
Otherwise, never reach inside that tower for any reason, even 
momentarily, regardless of the rationalization!

The following link is for a double worm gear rotator, but the worm gear 
photos apply to most worm gear reductions. Note the sharp edge (end) of 
the worm in the third photo from the top. 
http://www.rogerhalstead.com/Gears.htm

Some assemblies make the following difficult.

Next step: clamp the pull cable securely without damaging it, (try to do 
this without interfering with the cable drum) then disconnect the gear 
box from the motor. *CAUTION* this can be*hazardous to you, the tower, 
****and the antenna* if the cable clamp, block, or what ever holding 
things slips.  IF the motor runs then:
*
**NOTE:* You can clamp the drum, but they are often easily deformed and 
it may make other steps difficult.  It may be more difficult to reliably 
clamp as well.  Safety first!

  Either remove the entire gear box (best choice), or "if possible 
reconnect the gear box to the motor and disconnect the gearbox from the 
cable drum.  Can the shafts be turned? If not, find the instructions for 
the gearbox repair.

If you are not mechanically inclined, as many are not, seek 
knowledgeable help from the tower manufacturer, the gear box 
manufacturer, or a well known, good, local mechanic.   You are already 
into the realm where a mistake can be dangerous and */ *or very 
expensive, but gear boxes, whether crude, or precision and rugged can 
get expensive and worm gears can be finicky about disassemble as well as 
reassembly.

The worm gear "wheel" on the good ones will be contoured to fit the 
radius of the worm.  (Photos 1, 6, 9, and 13 in the above link) IE, the 
worm sets "down" into the worm gear wheel and can not safely be removed 
to the side without first raising the worm out of the wheel, or moving 
the worm gear wheel. *SOME* worms can be pulled straight out along their 
axis and some can't.   The one in photo 3 can.   Those that can, often 
have a razor sharp edge at the end of the worm (Photo 3) so be careful. 
To be safe resist the urge to feel the end of the worm for burrs with a 
bare finger, or catching it in the palm of a hand without a leather 
glove. Lots of oil, so be prepared to ruin a pair of gloves.  They do 
need to be clean to start.

How much applies to this problem could be all, or little, but it's a 
place to start.

73 and Good Luck!

Roger (K8RI)


On 1/29/2016 Friday 4:15 PM, K7LXC--- via TowerTalk wrote:
>>>   The Hub City W300 gearbox on my US Tower 85 ft  rotating  mast appears
> to have seized after 12 years.
>
>>    Are you sure you don't have a bad bearing in a pulley (sheave)?
>   
>      The UST pulleys all use sealed bearings and they  have been pretty
> reliable in my experience. Also the pulleys are also mostly  hidden so it's not
> easy to ascertain whether they're turning or not.
>   
> Cheers,
> Steve      K7LXC
> TOWER TECH
> _______________________________________________


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