[TowerTalk] Battle of the bearings

[Roger (K8RI)]

Mike wrote:
> Roger (K8RI) wrote:
>>
>>
>> Mike wrote:
>>> Thanks for the ideas and discussion guys. Food for thought.
>>>
>>> Can anyone address the 2 points I asked about?
>>>
>>> Rohn vs Glenn Martin bearings:
>>> http://www.texastowers.com/rohn_tb.htm
>>> http://www.glenmartin.com/catalog/page195.html
>>>
>>> Is a Rohn rotor shelf beefy enough for the bearings?
>>>   
>> Remember it's a ROHN shelf in a ROHN tower with a ROHN bearing.  
>> According the ROHN the bearing is for side loads and as it's a 
>> complete ROHN system I'd stick with their recommendations. IOW the 
>> shelf is plenty sturdy for side loads and will "probably" support 
>> quite a load. However check the difference in the thickness of the 
>> tower top plate compared to the shelf.
> The idea that the bearing is designed to obviate lateral motion just 
> doesn't make sense to me. I believe it's there to take the vertical load.
That used to be my understanding, but with the ROHN bearings I have to 
go with their instructions...(Prime directive). OTOH tapered bearings 
like wheel bearings are made to take lateral and axial forces. The PST 
series of rotators use bearing like these with the tapers pointed in 
opposite directions and use shims to keep the worm gear wheel centered 
in the worm gear.
> I wonder if a PE came up with the idea the bearing was for lateral 
> snubbing, or if it just came out of  somebody's misunderstanding, and 
> got codified.
>
> TWO bearings would keep the side loads off the rotor (or a long 
> sleeve, or two short sleeves.). A single bearing is just gonna be a 
> fulcrum.
Agreed.  Even a single sleeve is a fulcrum at its center. The rotator 
serves as the other end to prevent bending.  In this case the rotator 
receives a straight horizontal force instead of the bending/angular 
moment if it were mounted at the top.
I think most rotators can support a lot of weight.  The PST series can 
support tons.
>
> So I'm mule headed. ;-o
I'll have to take a reservation on that observation<:-))
>>
>> If it were me (and it's not) and I planned on letting a thrust 
>> bearing support load down in the tower, then depending on the load 
>> I'd use the ROHN shelf, or for heavier loads make a custom one out of 
>> 1/4" or even 1/2" steel plate. The shelf for the 25G is considerably 
>> lighter than the one for the 45G, but the 25G isn't meant for 
>> supporting a lot of weight.  OTOH it depends on your definition of "a 
>> lot of weight".  I don't consider 200-300# a lot of weight and would 
>> expect the shelves of either to support that much. BUT I'd not put 
>> that much weight on a 25G.   Check the catalog for ultimate ratings 
>> of each tower.
> I'm looking at a max of 240 lbs, if I go with the chrome-moly mast.
I think most rotators are rated for that load although they may not be 
rated for the wind load.
>
>>
>> As I've said before, I use two bearings, but the system destroyed one 
>> TB-3 and the second isn't in great shape so I'm going with sleeves 
>> welded to 1/4" steel plate drilled to mount on the ROHN shelves. I'll 
>> use collars to keep the mast from dropping or turning with the 
>> rotator removed.
> Sounds like a good plan.
I hope so.<:-))

73

Roger (K8RI)
>
> 73, Mike NF4L
>