[TowerTalk] Battle of the bearings

[Mike]

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. 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.

So I'm mule headed. ;-o
>
> 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.
>
> 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.

73, Mike NF4L