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Re: [TowerTalk] Bearings for Axial Load

To: towertalk@contesting.com
Subject: Re: [TowerTalk] Bearings for Axial Load
From: Grant Saviers <grants2@pacbell.net>
Date: Sat, 15 Jul 2017 19:42:29 -0700
List-post: <mailto:towertalk@contesting.com>
Agree 100% for top of tower mast restraints - use a UV resistant plastic or paint it. UHMW is cheap and almost as slippery as TFE, HDPE/LDPE slightly more $ and friction, Delrin/acetal even more $ and friction (still low) but a dream to machine, nylon in the ballpark of acetal. Most plastic cutting boards are HDPE or LDPE, stack a few.

However, for the bottom bearing of a rotating tower, it probably gets to a pretty large piece of plastic and careful engineering to handle the load - could be 40,000lbs thrust.

The spherical roller bearing spec request that started this thread is rated a 65k# radial but so far no post has offered its axial spec, and most likely it will be less than the radial limit. I did find an SKF spherical roller thrust bearing in about the same size (2.9"id) and it was rated 135k# thrust. A different animal, however.

I suspect the RTS bearing is ok for 55G since the max leg compression is about 18,000# plus a safety factor. But specs are lacking for the bearing. One issue I've been told about with rotating towers but never done or seen done is how to replace the bottom bearing without taking the tower down.

Grant KZ1W


On 7/15/2017 9:57 AM, Charles Gallo wrote:
This whole thing brings me back to one of my hobby horses.

Why are we using ball/roller/taper bearings for this use?

A nice hat section (inverted) plastic bearing (cheap if molded, more expensive 
if machined due to waste) made of say nylon 66, or even Teflon (particularly if 
filled) would be way better. They won't fret from vibration, never need lube, 
designed right won't see sunlight, never corrode , and would probably be less 
expensive in production quantities (see molded). I could build something that 
doesn't use solids, but multiple pieces of rod ends that would have more labor, 
but less material cost

Ball/roller bearings are great, but are really the wrong thing for an 
intermittent duty, low speed, weather exposed, hard to maintain environment, 
with vibration and shock when stopped

--
73 de KG2V
Charlie


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