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Re: [TowerTalk] Replacement Thrust Bearing

To: George Dubovsky <n4ua.va@gmail.com>
Subject: Re: [TowerTalk] Replacement Thrust Bearing
From: Patrick Greenlee <patrick_g@windstream.net>
Date: Sun, 19 Apr 2015 12:58:05 -0500
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>
That is correct, George. I reported the ID as nominal 2 inch and tube OD figures are often given nominal values. If you read the fine print, if available, various supplier's actual OD on tubing varies as well. It is easy to buy bearings and tubing and not be able to assemble them without a little sanding. The "Other Ham" in our Zip Code got a very nice slip fit on the mast material he selected. How I fare remains to be seen.

Luckily the RPM is so slow that a slightly undersized tube locked down by the bearing's set screws but not well centered will be just as smooth turning as a perfectly centered one if there is much distance between the rotator and the thrust bearing. In my instance the difference will be undetectable between a sloppy fit and a friction slip fit. Worst case I would have to take a little metal off the ID of the bearing to be able to get the tube through the bearing. Easily done by rotating the bearing and applying emery cloth carefully to the ID. I say carefully as the metal of the bearing ID is not particularly hard or difficult to sand in my experience.

My mast requirement is:
A 2.0" Dia x .250" wall 1026 DOM mast (yield = 85 Ksi) which will give me a safety factor of 2.57 for a DB42 antenna (38.9 SqFt Effective Area) mounted 2 feet above the tower top when the tower top is 94 feet above ground. This is per ANSI/TIA-222-G, Exposure Zone C, on flat terrain in Pottawatomie County, OK which is a 90 Mph wind speed zone.

Although my crank-up/down tilt over Tash Tower is 54 ft tall it will be mounted on a steel structure 40Ft above grade (first choice) or a bit lower if my mech engineer friend/consultant doesn't approve the "full height (40 ft)" plan.

Patrick    NJ5G

On 4/19/2015 11:57 AM, George Dubovsky wrote:
Towertalk,

One thing to remember about real bearings is that they are precision parts. A 2" bore bearing will be 2.00x ID, with x being a small number like "1". A galvanized or painted real 2" tube mast will likely not fit that bearing.

73,

geo - n4ua


On Sun, Apr 19, 2015 at 12:24 PM, Patrick Greenlee <patrick_g@windstream.net <mailto:patrick_g@windstream.net>> wrote:

    I have a NIB 2 inch ID bearing in a 4 mounting hole pillow block
    with grease Zerk.  It is one HD unit rated for way more than
    needed and cost about $20.  The box is labeled CJ Bearings and is
    part number UCF210-31.  There are only two hams in our ZIP Code
    and we went together and bought two. His is in use and doing fine
    while mine awaits the arrival of my repurposed prop pitch motor,
    SteppIR DB42, and Tash Tower HD LM354.

    The box has this statement printed on a side panel, "Do not open
    until ready to use, keep dry and clean."  I will be assessing the
    methods/repurposed plumbing components mentioned here as used for
    protection against the environmental hazards.  I have a hard time
    understanding the rationale behind paying near or over $100 for a
    bearing very similar to mine.  Maybe if I framed and displayed a
    high dollar sales receipt from DXE or a tower company perhaps that
    would help justify the price. ;) ;)

    After all, a little frog that has been hand raised, dew picked,
    and lightly killed is still just a crunchy little dead frog even
    if related processes read like the menu of a high dollar French
    restaurant.

    Patrick   NJ5G




    On 4/18/2015 11:04 PM, Roger (K8RI) on TT wrote:

        All of the new TB-3s and 4s I've tried felt very rough. A real
        bearing would be replaced if it were that rough, BUT the do
        the job well. Gene's suggestion are much better bearings.  My
        new (used, but new to me)LM470 has one of those mounted on
        top.  I'd suggest a cover of some sort to protect it from the
        rain.  They get rusty looking and look like crap, but continue
        to work well.

        73

        Roger  (K8RI)

        On 4/17/2015 12:49 PM, Robert Harmon wrote:

            I am overhauling my rotator and thought it would be good
            to replace my thrust bearing also.
            I have the Rohn TB3 bearing now.  It has been in use for
            18 years and feels pretty rough.
            Im thinking of going with a different bearing this time
            with a steel body and greased. (grease fitting)
            Looked thru the archives on tower talk to find out what
            others have used and can’t find much,
            on this type of replacement and I know the bearing supply
            houses have them, just haven’t
            pursued searching with them yet.   I would like to know
            what others have used.
            If you have used a thrust bearing like this,  could you share
            the number and supplier ?  Array Solutions has their model
            TB2 which is this type
            of bearing but it only has a two hole flange for
            mounting.  They have a larger unit with a 4 hole
            flange but it is for a larger diameter mast than 2 inch. I
            want a 4 hole flange but for 2 inch.
            Here is the info from their webpage:
            https://www.arraysolutions.com/Products/thrustbearing.htm
            Anyway, what say you ?


            thanks,
            Bob
            K6UJ
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