I have had 4 of the rotators fail, the bolts tear out from the base. It could
be fixed by opening up the mold to allow more material around the bolts. The
material is less than that the engineering handbook calls for. The bolts
should be nc not nf. We have cured the problem by welding a piece of 1''
thick stock to the botttom and use the Yaesu dampner.There has not been
another failure at W6BH since we did these mods.
J & J Antenna Service
> On Mon, 22 Mar 1999 18:18:19 -0800 dan hearn <email@example.com>
> >During a conversation w Mike a week ago he said that M2 abandoned the
> >donut shock absorber because the bolts loosened and gave trouble.
> He told me the same thing when my donut ( BMW vibration dampener) failed
> causing $1200 worth of repairs to the tower.
> However nothing loosened up in my case, the bolts all sheared off (
> probably from torque twisting) causing the mast to kick out and
> fracturing 2 legs of 45G with a KLM 40M4 and a CC 204CD hanging over at a
> 30 degree angle. A scary sight at 160' up.
> The rotator was mounted at the bottom of the top section and 2 thrust
> bearings were used.
> I dont know if I should try the donut again with aircraft grade bolts,
> etc or just hard mount. Bolt expense is a non issue but future damage is!
> The tower has been extended to 180' and I have no particular desire to
> climb on a weekly basis to check everything.
> Any ideas out there? How about castle nuts and cotter pins in lieu of
> safety wires?
> >also said
> >that rotator mounting bolt loosening is a frequent problem. They have
> >some commercial rotator systems w drilled head aircraft grade bolts
> >safety wired.
> >These are very expensive. He also said they are looking at some sort
> >of sheet
> >metal plate with bend up tabs as used on some automobile assemblies.
> >He suggested
> >using RTV on the bolt heads rather than Loctite. This can be cut away
> >with a
> >knife if removal is necessary. He feels that it is necessary to
> >periodically do
> >maintenance tightening of bolts.
> I wonder if the grade of the stainless bolts is causing stretching? I'm
> no mechanical engineer but wouldnt a galvanized and hardened steel bolt
> be better?? Ive been on many commercial towers and cant ever remember
> seeing stainless hardware. Several friends in the 2 way radio and tower
> biz refuse to use stainless.
> > I wonder if the different thermal coefficients of aluminum and steel
> >cause some
> >of these problems. I like the use of lock washers to accomodate small
> >changes w temperature. Double nutting, as suggested by Steve , is
> >certainly a
> >good practice.
> Rohn supplies a lock nut for many of their accessories; does everyone use
> them? (-:
> 73 Carl KM1H
> 73, Dan, N5AR
> >K7LXC@aol.com wrote:
> >> Greetings, TowerTalkians --
> >> Other than a prop pitch, the Orion 2800 is about the best
> >> rotator available but I've run across three Orions in the last
> >couple of
> >> months with the same problem. And that is, in spite of having the
> >best and
> >> beefiest mast clamp in the world, all three of them had loosened up
> >and the
> >> antennas were being turned by the wind. One was a TH11, one was a
> >C-4XL and
> >> the other was an M2 2L 75M yagi.
> >> In all cases, the nuts on the long bolts through the mast
> >clamp had
> >> loosened up. And all of these nuts were the nylock ones supplied by
> >> factory and also had spring lockwashers. These were both versions -
> >the fine
> >> threaded and the coarse threaded ones so they are both subject to
> >the same
> >> problem.
> >> While re-tightening them is great, I think it is inevitable
> >that they'll
> >> loosen up again. In the case of the 2L 75M, it went through almost 2
> >> before coming loose.
> >> Anyone using this rotator should plan on taking added
> >precautions to
> >> prevent this. In my cases, I'm going to double-nut everything.
> >Another option
> >> would be to use some Locktite (sorry - I can't remember if it's the
> >blue or
> >> red to use). Or do both. In any case, you won't be sorry.
> >> Cheers, Steve K7LXC
> >> http://www.championradio.com
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