[TowerTalk] Yet another worm gear box failure...

[Rich Hallman - N7TR]

I just checked two of my crankups and the HDX-689 has a Hub City 381 60:1 reduction....and the HDX-589 has a Hub City 321 60:1 Reduction.

The HDX-572 is painted over and cannot see the model...Im going to replace that box since I think this is the original Tristao model.

73  Rich N7TR

-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Ray Benny
Sent: Saturday, October 13, 2012 12:36 PM
To: Scott MacKenzie
Cc: KJ6Y at aol.com; towertalk at contesting.com
Subject: Re: [TowerTalk] Yet another worm gear box failure...

I've witnessed two such failures, both were on older Tristao towers.

The first happened during the hayday of the N6DX Mallibu hilltop contest station. We were raising a 72ft Tristao tower using its electric winch system, got about 2/3 up and crack!, the tower started to collapse into itself. Of course, we ran away as fast as possible. The fault, the weld on the 1 inch shaft to the multi-groove pulley broke. All tension on the cable was released so down it came. The tower was destroyed. At the time the tower was loaded with a tailtwister rotator, 15ft mast and 4el yagis for 20 & 15m. The antennas were repairable with a lot of work.

Just recently, my old Tristao, CZ471 collasped into itself. The fault, the flange idler bearing that held the 1" drive shaft dead -end in place pulled apart releasing tension on the raising cable. Just a few days earlier, I had replaced the old bearing with an American made Dodge bearing.. This bearing was made of pot metal while the original bearing was made of a single piece of steel machined with the roller bearing pressed in. The tower is beyond repair. It was loaded with with tailtwister rotator, 16ft mast, a C4SXL large tribander, and a full size 2el 30m yagi. I'm guessing total weight was about 300 lbs. Again, antennas are repairable but with a ot work.

My recommendation, if anyone has the old multi-groove drum/Hub city raising system (pre '80s, not sure of this date), replace it as soon as possible with a newer version  from either US Towers or Tashjian towers.

Ray,
N6VR

On Sat, Oct 13, 2012 at 10:46 AM, Scott MacKenzie <kb0fhp at verizon.net>wrote:

> Any one have any quality photographs of the shaft failure?  I am 
> looking at photographs of the fracture surface.  That should tell us 
> the mechanism of failure.
>
> Scott
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of  
> KJ6Y at aol.com
> Sent: Saturday, October 13, 2012 1:37 PM
> To: dino at kx6d.com; towertalk at contesting.com
> Subject: Re: [TowerTalk] Yet another worm gear box failure...
>
> Mike's tower sounds like the shaft broke and not a gearbox failure.   On
> the older MD-750 motor drives, the shaft was 1 inch coming out of the 
> gearbox. (Tristao and then US Tower).  US Tower then went to a larger 
> shaft, 1 1/4 or 1 1/2, don't remember which.  Have not seen any of the 
> newer ones fail.
>  There is a lot of tension on that multi groove pulley,  especially 
> when hams have a tendency to overload their tower. It's not just wind  
> load but weight.  Those towers have a weight limit.  Add it all up,  
> mast, rotor, antennas, cables, etc and I'm sure you'll see more weight 
> then you  thought.
>
> Regular maintenance and inspections should be done.
>
> Skip, _KJ6Y_ (http://www.kj6y.com/)
> _Communications Service Co_ (http://www.communicationsserviceco.com/)
> 818-887-3569
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