[TowerTalk] Which Thrust Bearing to Use

[jimlux]

On 12/9/16 8:13 AM, Hardy Landskov wrote:
> UHMW PE has a horrible coefficient of expansion. I don't know about
> Nylatron.

But this isn't a micron clearance kind of application,is it?

  Aluminum is  22 ppm/degree C
  Steel is 12

UHMW PE is about 100

Nylons without glass seem to be in the 75-100 range

Acetal with glass filling is about 39 ppm, w/o the glass it's 106

So, let's assume grungy regular "plastic" is about 100 (although getting 
a good glass filled, UV resistant wouldn't cost much more and would 
probably be a better choice for other reasons)


SO let's take an example of a 2" diameter mast.  going from -40C to 60C 
is 100 degrees, and probably wider than the range most ham towers will 
see.  So that's a change in diameter of, worst case 100*100 ppm or 1%

Your 2" hole that just clears at -40 will be 2.02" at +60C.  I don't 
think you're going to have a big problem with that 10 mil extra clearance.

If you have a 20 foot mast sticking up above the top, and 5 feet in the 
tower, that 0.02" slop will turn into 0.1" at the very top of the mast.




> N7RT/4
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of
> charlie at thegallos.com
> Sent: Friday, December 09, 2016 11:06 AM
> To: George Dubovsky
> Cc: towertalk; charlie at thegallos.com
> Subject: Re: [TowerTalk] Which Thrust Bearing to Use
>
>>  >I would expect either
>>> tapered roller bearings, or today, do what most of industry does, and
>>> use an engineering plastic bearing.
>>
>> And, in fact, that's what I do. One mast has a brass shaft collar that
>> rides on a slab of Nylatron (GS grade I think), and the other mast
>> uses a scrap TB-3 that was machined to replace the ball assembly with
>> a Nylatron sleeve insert for axial and radial thrust. I expect both of
>> them to outlive the towers they're sitting on... ;-).
>>
>> 73,
>>
>> geo - n4ua
>
> Yeah, I suspect they will
>
> I'm sort of surprised however that they aren't made that way, although by
> FEEL, that may be how the Yaesu thrust bearing is made.  Heck, a piece of
> UMHW PE would probably work too.  As I said, not a real high load situation.
> You have room for LOTS of square inches of plastic, which will prevent any
> creep so you don't need the high bucks stuff like rulon or vespil (shudder
> when you price vespil), it'll never rust, it never needs lube, doesn't
> matter if it gets wet
>
> Looking at the design of the DXE bearing, and the TB3 - the DXE is a true
> THRUST bearing - aka designed for a load along the axis of rotation (aka
> carry weight off the rotor), where the TB3 is really just a regular bearing
> for side to side loads.  To be BOTH, they would really need to be angular
> contact, or use a flanged plastic bearing, so it has bearing surfaces in
> BOTH directions, and get the best of BOTH worlds
>
> Heck, if I was designing a rotor today, or say updating the Ham V series
> (including the TX2), I'd use plastic there too, with the added advantage of
> it tending to act as at least a partial water seal.  Never did the math for
> what plastics you'd need keeping the contact size the same
>
> I mean nylatron is practically begging for that use.  No elevated temps
> (folks reading - elevated temps here means greater than 50C on a continuous
> basis aka 20 hours at a time - and even then, if we go reinforces with
> either glass or Molly, you can go 75c - just in case you want to paint your
> bearing black and put in in the sun in the Mideast), "moderate" loads per
> square inch, low rotational speeds, no seriously significant shock loads.
> Never have to worry about the balls indenting the races like the Ham IV,
> never have to worry about rust etc.  MFJ could get rid of the two steel
> races, the balls, the retaining rings etc, and have a better product for
> probably less money
>
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