[TowerTalk] Thrust Bearing Question

[Jim White, K4OJ]

> Do I understand correctly....that the thrust bearing (a) takes the weight
> off the rotor,

Not at my QTH, I personally do not but many hams DO use it in this manor.

A typical ham rotor can more than handle the weight of a heavy duty mast 
and antennas - it is the HORIZONTAL thrust that I use the bearing for - 
keeping the mast vertical and not allowing it to rotate eccentrically.

Why not use it for vertical bearing - the tower, the rotor plate and the 
rotator casting are all possibly "not perfect" - so it is possible 
things could be off square and off center... if this is true then it is 
conceivable that such an eccentric rotation would cause a rotating mast 
to have a vertical travel component...

IF there were indeed a situation where the mast wanted to go up and down 
and the trust bearing was securing the masts vertical position then it 
would be up to the rotator to go up and down meaning that since it is 
bolted to the rotor shelf, the shelf would then go up and down...

Now if all those bolts are doing their job they ain't allowin' any up 
and down and the casualty would be the housing of the rotator which does 
not allow any up and down - AND - since it is pot metal - well - can you 
say "weakest link?"



  and (b) allows removal of the rotor while leaving the mast
> and antennas in place?  Any other purpose(s)?


I could  use those set screws on the thrust bearing to hold the vertical 
weight of the mast while servicing but personally prefer to use a 
surplus HyGain toothed boom to mast clamp.

By elevating the mast only a little bit and then socking down that clamp 
you remove any load to the rotor and it can come free.  I have an 
automobile jack that is screw drive - I place it on the top of the flat 
plate and then operate the jack by my cordless electric drill - which 
easily will raise up the mast during rotor swap out/service.  The motor 
doesn't even sound strained - it is a beautiful thing - whirrrrrr up.... 
whirrrrrrr down.  I use it to push against the boom just above the top 
plate... no major muscling of the mast/stack is need - the cordless 
drill is doing the work :-)


> 
> I have the good fortune to have a tiltover tower, so I can install
> everything while it's horizontal, with no load on the mast. is 1/2" enough
> of a gap to leave in the mast-to-rotor connection?  Do I then just tighten
> the thrust bearing set-screws as tight as I can? Or is there more to it? (My
> thrust bearing didn't come with instructions, and I've never done this
> before.)



Again, a lot of guys do this - it is one of those topics on tower talk 
that once again I am sure reveal there are several different schools of 
thinking on the issue... since I decided to drop out of engineering 
school I will only qualify my thoughts as being those of a guy who has a 
very large contest station with multiple rotors and towers and the only 
rotor malfunctions I have endured are by virtue of lightning strikes 
opening up wires, etc...


GL

Jim, K4OJ