Personally for my towers, I do both at the same time.
If I put the weight on the rotor, then I'll have to jack the mast up a bit to
remove the rotor,
Yes this is what most folks do.
whereas if I put the weight on the thrust bearing I can remove the rotor
without raising the
mast.
Maybe, if there is enough clearance within the tower to move the rotator out
between the braces.
But it seems to me that it may not be such a great idea to have the weight of
the antenna and mast supported only by the three screws in the top thrust
bearing. What's the general consensus on this?
You are correct. Those three little bolts should NEVER be used to hold up a
mast/antenna assembly. They are NOT designed for that; they are intended to by
used to only center the mast within the bearing. Read below for my solution.
Rotators are designed to have some load on them to seat the bearings.
Correct.
What I have done with mine is first install the rotator and then install the
mast slid down into the rotator, firmly bottomed out. I have a single thrust
bearing on the top plate. I center the mast in the bearing and then install a
stainless steel pipe clamp (from McMaster Carr) around the mast just above the
bearing and slid down onto the bearing. I tighten this up and then install the
antenna onto the mast. Now this added load from the antenna is taken up mostly
onto the bearing and some additional goes to the rotator.
I don't have the second thrust bearings under the top plate because why would
they be of any use?
You certainly wouldn't want to have one and use just it's three bolts
incorrectly to hold the mast/antenna while you remove the rotator; I wouldn't
put my fingers underneath anything like that with only three (or even six if
you also used the three on the top bearing) bolts. To jack the mast out of the
rotator, I can do that two different ways. One I can install a small scissors
jack on the top plate underneath the antenna's boom to mast plate and jack it
up that way and then secure the mast at the top with another pipe clamp (or
move the permanent one down temporarily). The other way is to install a pipe
clamp on the mast just above the top of the rotator. Then string a come-a-long
on the inside of the tower from the top plate or brace near the top and use it
to slowly, in a controlled manner, jack the mast assembly up. Works like a
champ.
I have seen some setups where two bearings were used and the mast secured to
both and just a small stub of mast extended into the rotator clamp. Also a
brace was removed such that the rotator could be easily slid sideways. Trouble
was, in a well installed system, using good parts, we shouldn't have to be
messing around with this stuff very much.
--
Phil - KB9CRY
Lockport, IL
http://nidxa.org/memberWWW/kb9cry_home.htm
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