[TowerTalk] Further discussion of TB3

[K7LXC@aol.com]

In a message dated 03/06/2000 10:03:54 AM Pacific Standard Time, 
ValErwin@aol.com writes:

> I have heard the praises of the Rohn TB-3 for years from other esteemed 
tower 
>  experts such as you as well! What is so great about it over other 
bearings?   

     The over-riding reason that I recommend and use Rohn bearings is that it 
is intended for outdoor use; being aluminum and using stainless steel 
bearings makes it relatively impervious to rust. Any thrust bearing that uses 
an Allen screw to secure the mast is generally intended for indoor, machine 
shop-type pillow block applications. The Allen screw will rust and sometimes 
the bearings rust as well. They work great for a couple of years but 
eventually fail.  (The LXC Hardware Test: leave it outside for a couple of 
months. If rust forms, throw it across the fence and get rid of it.)

     This isn't to say that Rohn bearings don't fail because they do. Nothing 
rusts but the steel bearings can beat up the aluminum races as mentioned 
already.

     I think the over-riding question is 'what is the purpose of a thrust 
bearing?'. Any rotator has a vertical load capacity . If you've got a medium 
load and medium capacity rotator, they are probably matched capacity-wise and 
the rotator can handle the vertical load. The same holds true for a BIG load 
- you've got a BIG rotator (Orion, prop pitch, Big Boy<?>) and it also will 
handle the vertical load. If you don't need it to take the vertical load, why 
then, do you need a thrust bearing?
 
      A thrust bearing will take *some* side-thrust load. In this case, the 
TB is just being used as a bushing to keep the mast from flopping back and 
forth. This is a good use of a thrust bearing but you can do the same thing 
with a block of wood or any other 'bushing' arrangement. 

     So my answer to the question of "Do you need a thrust bearing?" is 
probably not.          

>  What is the hole pattern on the TB-3? Hole diameter for bolts? 

     It's a 4-hole pattern; I'll have to check to see what the 
center-to-center hole distance is.

> Does the TB-3  have a grease fitting? 

      No, it is not supposed to be lubricated. 

>  My current bearing with grease fitting is a Fafner 
>  (sp?) that I bought from a local bearing supplier here in the Dallas area. 
I 
>  cut a plastic funnel out that is WX-sealed (inverted) to the mast that 
rides 
>  bout' 0.25 inches above the bearing to protect  the bearing from the rain.

     That's a good technique but it ignores moisture condensation which will 
get in everything including the bearings. 
>  
>  I am planning on laying my tower over in the next few weeks and adding a 
40 
>  meter element to my CC X7. As my bearing is quite old,  I may use that as 
an 
>  opportunity to replace the bearing as a matter of preventative 
>  maintenance-whether it needs it or not.  

      I would say that you if you have sufficient clearance in the loosened 
TB to allow the mast to turn without binding, leave it as it is. Replacing a 
TB is a lot of work when you probably don't even need one in the first place. 

Cheers,   Steve   K7LXC
Tower Tech

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