[TowerTalk] [Bulk] Re: Clamp on thrust bearing

[Grant Saviers]

If the rotator is rated to handle the weight load of your mast and 
antennas, then you really don't need a "thrust" bearing i.e. one that 
accepts load along its axis.

However, you still need a "radial" bearing, one that centers the mast 
and resists side loads.  US Tower larger crank ups have no provisions 
for thrust bearings and the radial bearing is a galvanized steel sleeve 
for a 2" mast.

I use black delrin (acetal) or dark color nylon or black UHMW (ultra 
high molecular weight polyethylene) for radial bearings as all my 
rotators can easily handle the thrust loads, including a 350# 80m yagi 
with 170# 3" mast.

For a radial bearing you can take a plate of material that is large 
enough to fit over the existing thrust bearing mounting holes (or drill 
new holes in the top plate), bore it to the mast od (I go 0.040" over 
for the galvanizing and some clearance), drill the mounting hole pattern 
and then cut it in half on a bandsaw.  You can leave the bad "thrust" 
bearing above it held with a pipe clamp.

My bearings are 4" thick (see following).  2" thick or more are a good 
idea.  Black UHMW is my first choice material, cheap and slippery and 
reasonably UV resistant, but it is sticky and gummy to machine so takes 
sharp lathe tools and twist drills that are "daubed" so they don't 
grab.  Some folks propose using polypropylene or polyethylene kitchen 
cutting boards stacked to enough height. That is an easy way to go if 
the above materials are unobtanium, but paint either with a plastic 
compatible paint for UV protection.

One reason I use 4" thick material is that it will take some bending 
loads if I need to raise the mast to work on the rotator.  I have a load 
rated eyebolt in the top plate for attaching a hoist, but that still 
puts a side load on the mast.  After lifting to clear the rotator, I 
have a fixture from 2x2x 1/4" angles that centers the mast and keeps it 
from windmilling. I have a round flat plate above the radial bearing 
that accepts a thrust load from the plastic radial bearing so the hoist 
isn't required to hold the mast long term.  Of course that had to be 
installed on the mast when it went into the tower.  If you really need a 
thrust bearing, such as in a side mount arm assembly, then that plate 
can do that job against the plastic, again why UHMW is a good choice.

I've found all materials I've needed on ebay at good prices.

Grant KZ1W


On 11/1/2015 7:46 AM, jcjacobsen at q.com wrote:
> Ummmmmmmmmmmmm
>
>
> <SNIP>
> You might try loosening the Yagi mounting clamps and let them slide down
> the mast to the top of the tower. Then slide the mast up using a gin pole
> until you can insert the bearing. Then let the mast down and re-mount the
> beams. I think you will be much happier with a proper bearing.
>
> <Snip>
>
>
> Let's think about that........ You slide the yagi down to the top of the tower. Then raise the mast to insert the new bearing.
> This would mean the mast AND yagi would be above the top of the tower. What would support the mast and yagi while the mast is out of the tower??? Nope, don't think so.
>
>
> I like the idea of raising the mast out of the rotor just enough so you can place the bearing on the bottom of top plate. It would be easier to keep the mast braced vertical while doing it.... not to mention stable.
>
>
> Just my $.02 worth.
>
>
> K9WN Jake
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>