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

[Ray Benny]

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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