[TowerTalk] installing monster masts intowers(and? twothrustbearings)

Fri Jun 10 12:41:46 EDT 2005

Just to put in another anecdotal comment... all my masts have all their
weight supported by tb-3's with no weight on the rotors.  This includes 5
towers, the oldest has been up 20 years now.  Where I have flat tops I have
2 bearings, the top one uses the rohn bolts to hold the weight, the lower
one is loose unless needed to hold the bottom of the mast when removing a
rotor.

David Robbins K1TTT
e-mail: mailto:k1ttt at arrl.net
web: http://www.k1ttt.net
AR-Cluster node: 145.69MHz or telnet://dxc.k1ttt.net

> -----Original Message-----
> From: towertalk-bounces at contesting.com [mailto:towertalk-
> bounces at contesting.com] On Behalf Of Jerry Muller
> Sent: Friday, June 10, 2005 16:26
> To: Alan NV8A (ex. AB2OS); towertalk reflector
> Cc: Roger K8RI on Tower
> Subject: Re: [TowerTalk] installing monster masts intowers(and?
> twothrustbearings)
> 
> 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
> > _______________________________________________
> >
> > See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with
> any
> questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk at contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
> >
> 
> _______________________________________________
> 
> See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with
> any questions and ask for Sherman, W2FLA.
> 
> _______________________________________________
> TowerTalk mailing list
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