[TowerTalk] Which Thrust Bearing to Use

[Grant Saviers]

The coefficient of UHMW linear expansion of 11e-5 in/in/deg F means 
0.011"/in/in for 100 deg F temperature change, which changes the 0.030"  
gap I machined at 3" nominal bore at 65 deg F to about 0.0135" at 15 deg 
F and to 0.0465" at 115 deg F (ignoring the change in the mast 
diameter).  Not an issue in WWA.

UHMW is unpleasant to machine to tight tolerances for that reason and 
because it is so slippery and springy.  It's hard to hold and rebounds a 
lot from the cutter edge.  Drills hog in unless dubbed. 
https://www.youtube.com/watch?v=8Ri6poVpQM8 for a good lesson and which 
I have scars to verify what happens.

Grant KZ1W

On 12/9/2016 8:13 AM, Hardy Landskov wrote:
> UHMW PE has a horrible coefficient of expansion. I don't know about
> Nylatron.
> 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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