I second what Jim wrote.
On each of my towers I use two TB-3 Thrust Bearings and also a separate
Rohn AS45 accessory shelf with a Muffler Clamp clamped tightly to the
mast. This easily supports the weight of mast plus antennas while the
rotator is being swapped out, or taken out to lower/raise the mast for
antenna work. It also has the added advantage of if/when the Thrust
Bearing needs to be replaced or reconditioned or loosened for some other
reason, the shelf plus galvanized muffler clamp can easily support the
weight safely and you can actually tilt the mast within the top of the
tower to allow greater access to replacing anything.
It gives many options to the climber while at the same time increasing
safety and convenience at every step in the process.
It's relatively cheap insurance that protects the antenna and rotator
installation as well as the people doing the work at the top. If you
use a second Rohn Accessory Shelf on a very long heavy mast, it is even
easier and safer to do the work and you may not even need to loosen a
Thrust bearing as most of the weight can be is resting on the shelf at
all times. Depending on your installation, you might not even need a
Thrust Bearing at all! The muffler clamp provides a convenient
attachment point for a comealong tool to raise/lower the mast.
My TB-3's have lasted a lot longer since I have started using the
accessory shelves and muffler clamps.
73
Bob, KQ2M
On 2025-06-22 11:57, jim.thom jim.thom@telus.net wrote:
Put a clamp around the mast, so it's sitting on top of the top thrust
bearing.
I would suggest using 2 x thrust bearings. one at top of tower, and
another 3-6' down the tower, with the PP below that.
On my rohn TB-4 thrust bearings (3" mast) the 3 x setscrews all rusted
out
and seized up. The ball bearings also started to grind, water got in
there..and that was < 1 year.
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|