[CQ-Contest] Rohn TB3 Junk

[k8cc]

At 09:42 AM 9/23/01 -0400, K5NZ at aol.com wrote:
>Anyone have a replacement for the worthless TB3 junk Rohn makes?  Everytime I
>have to pull a mast the set screws on my TB3 snap off because they are rusted
>to no end.  I'm about to install a new tower and want to buy something else
>this time. Why would a company use hardware like this that has to sit in the
>elements 24/7?

Mike,

If you think Rohn TB-3s turn into junk in the wx, you should see some of 
the alternatives.  When I first started putting up K8CC I would go and buy 
1-15/16 flange bearings from a bearing supply house which were a perfect 
fit for the 1-1/2" schedule 40 water pipe masts I was using at the 
time.  (Only single yagis on each mast right at the tower top so the mast 
strength was not important.)  The bearings themselves seemed to have no 
problem but the set screws and hardware rusted up worse than any TB-3 I've 
ever seen.  I have four TB-3s in the air here and never snapped off a bolt.

This is probably because I don't expect the TB-3 bolts to carry any heavy 
weights.  All of the masts holding my "big" antennas (> 100#) have what the 
machinery people call a "shaft collar", which looks like a donut with a 
square cross section, split in half and held together with high-strength 
allen head bolts.  When the shaft collar is tightened on the mast, it grips 
the mast very tightly, as its designed to do.  The collar is positioned to 
sit on top of the TB-3, thus transferring the weight of the mast/antennas 
to the top surface of the TB-3.

I've had these shaft collars hold the 100+ lb mast and a 250 lb 5L 20 on a 
52' boom with zero slippage during rotator repairs.  The collars cost 
something like $20 each if I remember right and work a heckuva lot better 
than the TB-3 bolts.

I cringe at K7LXC's suggestion of substituting stainless for the TB-3 
bolts.  Anyone who has ever had one of those yucky Ham-M mast clamp u-bolts 
gall up the nut and snap off would probably agree.  Stainless is pretty, 
but some of it is not very strong.  I question whether the stainless would 
work very well in the aluminum (or whatever alloy) of the TB-3 bearing body.


Dave/K8CC


--
CQ-Contest on WWW: http://lists.contesting.com/_cq-contest/
Administrative requests: cq-contest-REQUEST at contesting.com