[TowerTalk] mast weight on the rotor or thrust bearing?

[Phil Camera]

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