[TowerTalk] installing monster masts in towers(and? twothrustbearings)

Fri Jun 10 12:26:20 EDT 2005

Alan,

My masts (24 foot extending 18 feet above the top thrust bearing) all fit my
thrust bearings (TB3 and TB4) just about perfectly without locking bolts. I
have two thrust bearings in each tower separated by about 4 feet. The bottom
one is a few feet above the rotors (Prosistel PST-61s). I have no side to
side slop. If I had a situation like yours, I'd leave the bolts in but they
wouldn't be holding the weight of the mast, they'd be loose enough to allow
the rotor to bear the weight.

73, Jerry K0TV

----- Original Message ----- 
From: "Alan NV8A (ex. AB2OS)" <nv8a at att.net>
To: "towertalk reflector" <towertalk at contesting.com>
Cc: "Roger K8RI on Tower" <k8ri-tower at charter.net>
Sent: Friday, June 10, 2005 12:04 PM
Subject: Re: [TowerTalk] installing monster masts in towers(and?
twothrustbearings)

> On 06/10/05 03:43 am Roger K8RI on Tower tossed the following
> ingredients into the ever-growing pot of cybersoup:
>
> >>> Thrust bearings normally only need to handle side to side forces. The
> >>
> >>rotors
> >
> >
> > Agreed.
> >
> >
> >>can bear the weight of the antenna(s) and mast with no problem. KC1XX
> >>tells
> >>me that the locking bolts should all be removed from thrust bearings.
Let
> >
> >
> > I'd sure hate to do that in my system.   Look at my system and tell me
what
> > a half inch of side play in the  top bushing would do.  That's what I'd
have
> > if I took out those bolts as there is a quarter inch clearance all the
way
> > around the mast in the bearings..
>
> >>the rotor hold the vertical load and let the thrust bearings take the
> >>horizontal. My thrust bearings have no locking bolts whatsoever. No
> >>problems. When I need to take the rotor out, I put some U bolts on the
> >>mast.
>
> > There are different systems.
> > Mine extends 30 feet above the top of the tower and about 14 feet below
the
> > top.  The weight minus the rotator is over 600#.  The top bearing would
> > serve as a pivot point with basically a 2:1 multiplication.  That means
100#
> > side force at the top would be 200
> > # of side force at the rotator.  There is also 400 # of weight above the
top
> > bearing.  when it flexes that is an 800# force that would otherwise be
> > appled to the rotator.  The forces far exceed 100# at the top with 70
MPH
> > gusts and then the spring in the mast will start an oscillation.  The
> > rotator would be holding as much or more side thrust than the top
bearing
> > and it's not built for that.
> >
> > In 60 to 70 MPH winds which seem to be more common of late, that top
mast
> > looks like a blue gill rod that just tied into a bass.  I'm amazed the
> > antennas have held together after watching it whip around.
>
> >>   Amen to that, brother. My personal opinion is that mast vertical
thrust
> >>bearings are highly over-rated and don't really contribute anything of
> >>value to
> >>the rotating system other than a being a nice mast bushing.
>
> > Agreed again, but you don't want any play in them.  With the mass in my
> > system it'd destroy itself if the bolts were removed from the top
bearing.
>
> >>   IMO the amateur need for a special thrust bearing is sort of like the
> >>amateur perceived need for use of  the 1-foot long "torque arms" that
hams
> >>have
>
> > If you are talking about the 18" ROHN torque arms they achor at a single
> > point and are only relatively fixed.  You end up depending on the amount
of
> > torque used to tighten them in place.  The *star* system which extends
less
> > is far more rigid.
>
> >>put great value in for decades but in reality add little or nothing by
its
> >>use.
> >>(The Great Ham Radio Urban Legends?!?)
> >>
> >>   Rotators are designed to have some preload on them and their
bearings.
> >>Why do you think all those bearings are there in the first place?!? The
> >>T2X has
> >>NINETY-SIX of them.
>
> > A tail twister lasted a very short time on my system and the winds were
not
> > all that bad either..
> >
> > It went through two HDR600s in as many weeks, but that was due to the
poor
> > break setup and it's ability to free wheel with no stops. You have to
> > release the brake and then apply power.  In strong winds the antennas
are
> > already turning fast even if you try to operate the motor right after
> > releasing the break.  Those suckers just scream.
>
> >>   For the reasons posted previously, a mid thrust bearing is just a
total
> >>waste of money. (Unless you really did need that expensive bushing -
hi.)
>
> > Again, you need to do the math.  That bearing above the rotator takes
the
> > side thrust which the rotator is not designed to take. My rotator
supports
> > the load, but the bearings take the side thrust which is what they were
> > designed to do.
>
> >>   People SCREW UP bearings in different ways. If they'd have just left
> >>them
> >>off, they'd have been in better shape! And that's not speaking to the
bind
>
> > In many cases I'd agree, but there are antenna systems and then there
are
> > antenna systems.
> > I don't think I could even work on mine without the bottom bearing.
It'd
> > take a "comealong" to center the mast to get it in the rotator No way
could
> > I counter that top heavy beast by hand even on a calm day.
> >
> > Now if we were talking bushings that just nicely slip fit the mast, I'd
> > agree that no bolts would be needeed with the exception of when you want
to
> > do some work on the rotator.  OTOH it's easier to move the mast with a
> > comealong and lock it in place with the bearing bolts when working on
the
> > rotator.
> >
> > As for bind, with both bearings centered and tightened, I can loosen the
> > mast clamp in the rotator and turn the entire system with one hand (on a
> > calm day). I've done it when working on the pigtails at the top of the
> > tower. Of course this shifts the weight from the rotator to the
bearings.
> > I've also had trouble just holding it with a big strap wrench in just a
10
> > to 12 MPH wind.
>
> >>that can be easily introduced to the rotating system. And I take my
> >>hard-hat off
> >>to anyone who can measure 0.01" with an instrument on top of a tower.
Both
> >>of
> >>you.
>
> > You don't need to be any where near that.  1/16", or  0.065 is
relatively
> > easy to do. Of course that is over 6 times the 0.01".  Having worked in
a
> > shop, the 0.01" is considered a coarse measurement.
> >
> > Even a steel mast with a quarter inch wall will have enough spring you'd
> > never know the 1/16th was there over three feet.  If you have the
equipment
> > it matters not whether you are on top of the tower of in the work shop
to do
> > the measurements.  A magnetic base or clamp to hold the indicator (or
> > ruller) is really all that is needed.  I'd not use a dial indicator as
the
> > mast is not going to be true to begin.  A simple, fixed reference point
and
> > pair of calipers should be suficient.
> > However, given the proper equipment and a round mast almost any one
whould,
> > or should,  be able to measure to three digits, not two.  It just ain't
all
> > that difficult.
>
> >>   And don't get me started about the yucky eccentric collar TB that US
> >>Tower uses. They are really useless.
> >>
> >
> > Again we agree on this point.
>
> Roger:
>
> Maybe you've had somebody do the calculations and ascertain that
> everything is safe, but I definitely do not like the way your system
> sounds from your description: that's an enormous load on a long piece of
> tube sticking out the top -- and on the top section of tower above the
> uppermost guys.
>
> I'd rather go higher with the tower itself and keep the mast to a much
> more reasonable length: 2" CM tube is almost as expensive per foot as
> additional AN Wireless mast sections,
>
> 73
>
> Alan NV8A
> Zeeland, MI
> _______________________________________________
>
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>
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