[TowerTalk] aircraft bearing

[W0UN -- John Brosnahan]

Lots of questions and little time.  Most ham rotators will take the 
vertical load
just fine.  In fact it is hard to have two bearings share this 
load.  But you are
correct in that most people mean the horizontal load -- or the THRUST from
the WIND!    ;-)

Here is a quick verbal try at the dual purpose bearing.  Take a block of
UHMW and bolt it to the top plate of your tower.   This stuff is rated at
about 2,000 (to 3,000) psi load, so a one inch thick piece with a 2 inch
mast is good for 4,000 (to 6,000) pounds of side thrust.  Now on top of
this block of UHMW put a SMOOTH sheet of metal like a very large
fender washer.  Something with a two inch hole and four to six inches
in diameter.  Transfer the vertical load of the mast by clamping a pair
of back-to-back muffler clamp saddles together on top of this washer
and the clamps and washer will turn very smoothly on the UHMW.
VERY CHEAP.   Of course you can make something more sophisticated
than back-to-back muffler clamp saddles, but these will work for most
ham loads.

So now the $5 6x6 block of UHMW is supporting both the side and
the vertical loads (no matter what you call them).  You need to bolt
the UHMW to the top plate with more projected area of bolts than
the mast has.  IE, if the mast is 2 in OD then you need a total of
four 1/2 inch bolts or better--so that the psi rating of the bolting system
exceeds the mast.  Or build a cage around the block of UHMW from
angle iron.

I'll reread your note when I get back and see if I missed something.
My wife is trying to get me into the shower so we can leave for a
dinner party.

73--John


At 01:33 PM 7/31/2005, you wrote:
>Hello John,
>
>I had the pleasure of getting a free tour of Alpha by you when I was 
>living in Colorado.  I will never forget that!
>
>On to bearings...
>
>I've been reading this thread with great interest.  I wasn't getting 
>it at first.  Sometimes the term, "thrust bearing" gets confused in 
>the tower arena.  "Thrust Bearing", in my vocabulary, means taking 
>on SIDE loads in one dimension, like a thrust bearing in an engine 
>that prevents the crankshaft from moving fore and aft, but not 
>responsible for supporting that crankshaft.  When we speak of tower 
>masts, we take on loads in two dimensions; vertical and side.
>
>So this is how I try to separate the two (your mileage may vary).
>
>   The "bearing" used to take the side loads, I call, a 
> "BUSHING".  I believe the majority of this thread was dealing with 
> this type of bearing.  Simply, it's a 1" thick triangle plate, the 
> size of, and bolted to, the top/rotor plate.  The center of this 
> plate is drilled to accept the 2" mast and prevent it from touching 
> the tower's metal parts.  We rub the bearing rather than the metal 
> tower parts.  On the top of a "pointy" Rohn section, I've used a 
> piece of PVC pipe, the length of the tower tube, as a bushing.  In 
> both examples, they only provide support in one (side) dimension.
>
>   The "bearing" used to take the vertical loads, I call the THRUST 
> bearing.  It's just like the crankshaft, only flipped up vertical.
>
>(As a side note, it's my feeling that the majority of the bearings 
>(fanfir) used to support the vertical load of the mast and antennas 
>is used incorrectly.  They were designed to support horizontal 
>shafts parallel (load) to the flange, not how we use them.  But, 
>they seem to work OK.  A taper bearing would be a better option.  IMHO)
>
>What I don't fully understand at this point, is how the UHMW 
>(plastic) sheet is used to support the vertical load.  I'm assuming 
>you are using 2 sheets.  How is the second sheet secured to the 
>mast?  If possible, a picture is worth a thousand words!  :-)
>
>Dino - K6RIX
>
>-----Original Message-----
>From: W0UN -- John Brosnahan <shr at swtexas.net>
>
>If you end up using the UHMW to handle the vertical load as well, then
>the large "washer" that sits on top of the UHMW to spread the weight
>over a larger area will provide the UV protection needed.
>
>--John   W0UN
>_______________________________________________
>
>See: http://www.mscomputer.com for "Self Supporting Towers", 
>"Wireless Weather Stations", and lot's more.  Call Toll Free, 
>1-800-333-9041 with any questions and ask for Sherman, W2FLA.
>
>_______________________________________________
>TowerTalk mailing list
>TowerTalk at contesting.com
>http://lists.contesting.com/mailman/listinfo/towertalk