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
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.
On Sat, Oct 13, 2012 at 10:46 AM, Scott MacKenzie <firstname.lastname@example.org>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
> -----Original Message-----
> From: TowerTalk [mailto:email@example.com] On Behalf Of
> Sent: Saturday, October 13, 2012 1:37 PM
> To: firstname.lastname@example.org; email@example.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
> Regular maintenance and inspections should be done.
> Skip, _KJ6Y_ (http://www.kj6y.com/)
> _Communications Service Co_ (http://www.communicationsserviceco.com/)
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