I am a believer of the school that the thrust bearings are for sideways
thrust, not an element for the support of the weight of the mast and
antenna/e....
This belief is based in part on the reality that your mast is probably not
perfectly true or vertical, and your rotor shelf is probably not level flat.
If the above are one or both correct (true????????) the rotation of your
mast creates a situation where your mast, in relation to your rotor shelf, is
actually moving up and down to some extent as it rotates. If you tie your
rotor to the mast at the bottom of that up down cycle, and you begin
rotation, when the mast is at its high point you are actually trying to pull
the housing of the rotor apart!
Did you know that the very popular ham series of rotors is set up for a 2" OD
mast? Think about it - you are moving one side of that clamp only....and this
means that if you are committing the towertalkian sin of using 1 1/2" water
pipe which has an OD less than 2" you are turning that mast in an oblong
orbit! After 25 years of doing this that hit me recently. Oooooooooops -
QFU!
Solution, don't worry about the weight of the mast being borne by the
rotor....huh???? Check it out, read the spec sheets - the ability of almost
all commercial rotors to handle WEIGHT is very large, so - why sweat it? If
the mast wants to move in relationship to the rotate plate - so what...by not
pinning its vertical movement you don't stress anything.
But what about when you have to change out the rotor you say....easy: Keep a
Hygain 204BA boom to mast clamp (2-piece casting with teeth on the
inside....) handy and carry that up the tower when it is time....simply
tighten it down around the mast with its low side bearing on the top of the
tower's thrust bearing, or at the mid bearing's shelf if you like to use one
like (another towertalk thread) ....it will keep the mast from dropping when
you pull out the rotor.
Mind you I am NOT an engineer, and dropped out of ME studies in the second
term of college over 20 years ago (gawd I am an old fart with a two letter
call living in FL) ..this is just plain and simple common sense stuff, like
knowing to take an extra coupla 1/4-20 nuts and bolts up in your pocket when
you climb the tower - oooooooooooops!
Dissimilar metals - now that is a fascinating study....I can imagine your
headache having to cut a mast up in order to remove it ------> fun, NOT! I
am told that the hardness of a chrome molly steel mast is SO great that the
act of painting it is more for ones own psychological/cosmetic sake than it
is for corrosion prevension....but. of course we all paint it cuz it is just
one thing we CAN do!
The posts on the reflector about masts recently have been great, ya' know I
still am into this Heavy Metal stuff.............whoa the seventies, Rockin'/
Tower Workin'/ Drivin' to Dayton/ Traffic Handlin'/ Contestin'' and
BABES!!!!!!!!!! I don't handle traffic anymore, and the babes are grandkids
but ya know I still love contests and towers and when noone is lookin play
that air guitar to Stariway to Heaven on my car seat belt!
73,
k4oj
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