[TowerTalk] Rohn TB-3
Stan or Patricia Griffiths
w7ni@teleport.com
Mon, 10 Jul 2000 13:21:08 -0700
I have one additional suggestion for reworking a TB3. There is really no provision to
keep the Allen screw that plugs up the hole for the bearings to pass through in the
correct place over a period of time. It just "floats" in the threads. If it works its
way in further, it could jam against a ball bearing. If it works its way out further, a
bearing could drop into the hole that was created. You can fix this problem by securing
the "bearing hole" Allen screw with another set screw. Drill and tap a hole through the
bottom casting for a smaller set screw to be used to secure the Allen "bearing hole"
screw.
New TB3 bearings have been "fixed" by Rohn. They use a punch to deform the aluminum
casting near the threads of the Allen "bearing hole" screw. This probably works OK and
you can still remove the bearing hole Allen with a little extra force. You will need to
repunch it when you reinstall it, if you like that method of securing the bearing hole
Allen.
Stan w7ni@teleport.com
Jim Idelson wrote:
> Joe,
>
> The old style TB3 that I am familiar with has a set screw that is used to get
> the ball bearings in and out of the unit. As the balls pass the set screw, they
> may drop out of the channel momentarily. I would adjust the position of the set
> screw to get the smoothest action.
>
> The nuts are locking nuts. Put them on the bolts, tighten up the bolts on the
> mast, and tighten those nuts against the housing to help keep the bolts from
> loosening. Use some anti seize paste.
>
> Below I have attached my article from 1998 on refurbishing a TB-3.
>
> 73,
>
> Jim K1IR
>
> Date: Wed, 9 Dec 1998 10:18:51 -0400
> From: Jim Idelson <jimi@designet.com>
> Subject: Refurb Your Rohn TB-3 Thrust Bearing
> To: TowerTalk Post <towertalk@contesting.com>
> Mime-Version: 1.0
> Organization: DesigNET International, Inc.
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>
> FROM: Jim Idelson <jimi@designet.com>
> TO: YCCC <yccc@yccc.org>
> DATE: Wed, 9 Dec 1998 10:13:10 -0400
>
> RE: Refurb Your Rohn TB-3 Thrust Bearing
>
> Refurbishing Your Rohn TB-3 Thrust Bearing
> Jim Idelson, K1IR
>
> In the last two weeks, I've refurbished two Rohn TB-3 thrust bearings. One was
> running very rough. The other was "sticking" at several points in its rotation.
> After refurbishing, they both run very smoothly. This procedure is only
> intended to help improve the operation of a reasonably "healthy" unit. If you
> find serious problems, like cracked castings, broken or missing ball bearings,
> extreme wear, or cross-threaded screws - please do the wise thing and replace
> it with a brand new thrust bearing.
>
> Thanks to Fred, K1VR for providing the thrust bearings to rework, and the
> reminder that I should post this information for the benefit of all.
>
> Here's what you'll need:
> 1. A clear, well-ventilated, well-lighted workspace
> 2. A 16" x 24" or larger tin baking sheet with edges [so you don't lose the
> ball bearings]
> 3. A rag for cleaning
> 4. Mineral spirits for cleaning
> 5. 3/16" Allen key [preferably with a 6" handle and "rounded" end for insertion
> at an angle]
> 6. Miscellaneous filing tools [i.e. small hand files - round, flat; a Dremel
> tool with fine grinding capability]
> 7. Wrenches
>
> Procedure:
> 1. Remove all the bolts and nuts that secure the bearing to the tower and the
> mast into the bearing.
> 2. OVER THE BAKING TIN, CAREFULLY remove the Allen set screw located on the
> inside wall [where the mast goes through].
> 3. The ball bearings will begin to fall out of the set screw hole. Rotate and
> lightly shake the bearing to coax the ball bearings out of the hole.
> 4. The unit was built with 32 [THIRTY TWO] ball bearings. Make sure you have
> them all! Set them aside.
> 5. Separate the top and bottom castings of the bearing.
> 6. Clean both castings and all the ball bearings with the rag and the mineral
> spirits or other grease-cutting cleanser.
> Note: It is normal for some dirt and metal powder to accumulate. The bearing
> should not contain grease. This unit is designed to run dry.
> 7. Inspect the ball bearing races. Look for unusually worn areas, pitting,
> cracks. Try rolling a ball bearing in suspect areas to see if it will get
> "hung".
> 8. Using your filing tools, smooth out any rough areas so the ball bearing can
> roll without resistance.
> 9. Do this for both castings. Note that your mast will be pushing down on the
> upper casting. This will cause the bearings to press against the top of the
> race in the upper casting, and against the bottom of the race in the lower
> casting. Pay close attention to these areas.
> 10. Make sure you look carefully at the area of the race in the upper casting
> near the set screw. I found that wear in this area was causing one of the
> thrust bearings to stick.
> 11. Insert the set screw - don't cross-thread it! Adjust it to the point where
> a ball bearing can run across it smoothly. Note, from the insertion side, how
> far the set screw is screwed in. Remove the screw and set it aside.
> 12. Reassemble the thrust bearing by holding the castings together and
> inserting the ball bearings back into the set screw hole one at a time. You'll
> have to rotate and jiggle the unit to find space for the last 5 or 6 ball
> bearings. Do this over your baking tin so that WHEN [not IF] you drop a ball
> bearing, it falls in the tin, not in the air conditioning vent.
> 13. Replace the set screw. Insert it until it is at the point you noted in Step
> 11. It should be roughly flush with the inside wall of the upper casting. Be
> careful not to cross thread the set screw.
> 14. Now it's time to give the bearing a spin. It should run much smoother, and
> should not "stick" at all.
> 15. If you think the bearing could operate a little smoother, try adjusting the
> set screw in or out a bit. Remember, the ball bearings must go by the set screw
> smoothly.
> 16. If the unit still sticks . . . return to Step 2. If this is your second
> time through the process and you're still not satisfied - THROW IT AWAY and go
> shopping for a new one.
>
> 73,
>
> Jim K1IR
>
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> The Information Resource for Conferencing Professionals
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> To: <towertalk@contesting.com>
> Subject: [TowerTalk] Rohn TB-3
> From: "Joe Sloss" <sloss@mindspring.com>
> Date: Fri, 7 Jul 2000 18:20:07 -0700
>
> Am replacing a 30 year old Fafnir bearing TB-3 with the current style which
> just came via UPS. Quite a difference! Is it normal for the newer style,
> when exerting pressure downward, to rotate with a very slightly "jerky"
> movement like a bearing is not properly seated? The bearings sound "loose"
> when the unit is shaken. I assume the 3 each 3/8" bolts are for tightening
> down on the mast but what function and where do the 3 each nuts go? My
> older TB-3 had standoffs from the tower mounting plate; it looks like this
> one is just bolted flat against the plate. Comments gladly absorbed.
> Thanks, Joe K7MKS
>
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