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Thread: Need to make thrust bearing
12-26-2009, 08:13 PM #1
Need to make thrust bearing
I need to make two thrust bearing mounts for an antenna mast. I have two thrust bearings with a 2” id. What I am looking for is an idea or cross section view of how these bearings are retained and bolted to the plate of a tower. Any ideas or links appreciated.
12-27-2009, 03:12 AM #2
Do you want to rotate that mast ??
I would suggest 2 pillow block bearings and a single thrust bearing at the bottem to take up the load of the weight
But those pillow blocks can also take a lot of thrust load so you probably don't need a seperate thrust bearing
12-27-2009, 07:39 AM #3
12-27-2009, 08:45 AM #4
There are two different thrust loads for an antenna mast... vertical and lateral.
The vertical thrust bearing is built into the rotator, as a set of balls running in grooves just inside the perimeter. If you're using a gear or chain drive, then the bearing would just mount in a locating frame bolted to the tower plate.
Lateral thrust can be a much more serious problem. If you're running a single yagi for 440 on a 5' mast it's not much of an issue. But if you have an array of HF mono-banders, some serious engineering is required.
You should have two lateral bearings, one at the bottom of the mast just above the thrust bearing, and one as high on the mast as possible, usually fixtured in the top of the last tower section.
If you're supporting a large array, it's advantageous to mount the tower plate lower than usual, to increase the distance between the two lateral bearings thereby reducing the stress.
If I were doing it, I'd get a big block of stainless and bore out a hole for the lateral thrust bearing, with a smaller hole below it to accommodate the vertical thrust bearing.
Leave about 1/4" of material between the bottom of the vertical bearing and the bottom of the fixture, with some drainage channels or holes to let the water out. You don't want the bearings submerged in water.
Here's a little drawing of what I would do. Exact dimensions and mounting depend on your details.
So what are you putting up?
Good luck with it.
- 73 de Leigh W3NLB
12-27-2009, 09:14 AM #5
First, thank you for your interest in my request.
The bearings are INA/ANDREWS 2280 (NOS) purchased from eBay. One race ID. is slightly larger than the other, which I assume is to be able to accommodate an inside shield if so desired. The mast material is sch. 80 pipe with a nominal OD. of 1.9” . The expected height of the mast above the tower plate is around 5’ or so, with an overall length of 8’ to the rotator. At 3.631 pounds per foot for black pipe it equals 29 lbs. The weight of the antenna is yet to be determined, but should be no more than 100lbs.
The rpm of the rotator will be between, 1-3 revolutions per minute, able to turn 360 deg. with electronic preset stops to not exceed limits, clockwise and counter-clockwise operation on a horizontal plane relative to ground.
The overall idea is to relieve the weight carried by the rotator, to extend its service life and allow for easy removal of rotator from tower, if maintenance is needed.
What I am trying to accomplish is a bearing that is encapsulated inside a housing that can be bolted onto the plates of the antenna tower. Here is a link to a commercial thrust bearing.
Thanks again, KJ6CYD, Larry
and 73! to you too W3NLB.
12-27-2009, 09:59 AM #6
If you're really doing a 100-pound antenna, 3 rpm from the rotor would probably rip the top off the tower when you try to stop it, unless you're using a Rohn 55G or better.
Overall this sounds like a pretty light load for a good ham-grade or commercial rotor. It would be worth checking the rotor specs.
I've seen some worn rotors in my ~50 years of hamming, but all had been in service for a long time. There are other maintenance issues that might rear their heads sooner.
Good luck with it.
12-27-2009, 12:02 PM #7
The Field Day group I'm in has Rohn 25G tower with the Rohn bearing shown in the link on top. We use a TA 33 beam on 40' of tower and 4 or 5 ft of pipe above that. I have a truck with a crane and use a 20' extension boom on it to erect the tower. The bearing is pretty rough and does not absorb any thrust, just keeps the pipe centered. Since we only use it once a year, we don't worry about rotator life. In a permanent installation, I would want to do something better, especially re weather resistance. The bearing is open, just depending on overhang of the cap to keep water out. Since it is quite loose, a little rust doesn't have much effect. To use your bearings or any typical ball bearing, you will need to have a sleeve over it for better weather protection because a little rust in a close tolerance bearing will freeze it. You need a tube extending up from the tower plate several inches holding the outer race and a larger sleeve attached to the pipe hanging down over it and well sealed to the pipe. You will also need a collar attached to the pipe bearing against the inner race and I would really goo the bearing up with silicone grease, slopped on very heavily.
01-18-2010, 12:53 PM #8
Bearing housings are done.
Thanks for all the suggestions. I used the material I had available and they turned out nice. They are rain tight and should last for years to come.