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Re: [TowerTalk] Help with antenna

To: Ian White GM3SEK <>,
Subject: Re: [TowerTalk] Help with antenna
From: Peter Sundberg <>
Date: Thu, 25 Aug 2005 07:55:22 +0000
List-post: <>
I used cutting boards as low friction material for a couple of homemade guy
bearings I made for a rotatable tower. The material from the cutting boards
was screwed in place on the large metal rings.

The bearings have been out in the sun for many years without the material
disintegrating. I grinded (or should I say polished) the surface some, and
then greased it for even less friction.

My problem was that the tower was not stiff enough, it twisted badly
because there was only horizontal brazing (no Z-brazing) so I could not put
any large antennas on it. As it was an experiment I eventually took the
tower down and replaced it, but the bearings are still in perfect shape
waiting to be used again.

73/Peter SM2CEW

At 07:05 2005-08-25 , Ian White G/GM3SEK wrote:
>Jim Lux wrote:
>>Cutting boards (the white ones) are usually High Density PolyEthylene 
>>(HDPE) or UHMW (Ultra High Molecular Weight) PE. You can look up the 
>>material properties at somewhere like or any of 
>>a zillion plastics suppliers.
>>Real low friction (aka poor man's teflon), fairly good dielectric 
>>properties (somewhat lossy at HF and higher, compared to some other 
>>plastics) (It's great for HV DC insulators)
>Old cutting boards are also good for dipole center pieces, custom end 
>insulators, gamma arm supports and many similar applications.
>In these islands we can't speak much about long-term effects of 
>sunlight, but HDPE/UHMW does have the advantage of being a continuous 
>solid material, so it doesn't flake and de-laminate like fibreglass and 
>other composites.
>>The real problem with using it is that the melting point is quite low, 
>>which makes for trouble machining, and if it's going to sit outside 
>>with a static load because it will ooze.
>The ooze or "creep" problem can be minimized by making most of the 
>bearing out of metal, and using the plastic only as a facing for the 
>bearing surfaces; and also by taking care to spread the total load over 
>the largest possible area.
>However, as W0UN pointed out a few weeks ago, if you make the whole 
>bearing out of a big solid chunk of UHMW, that is enough to spread the 
>load. For most TowerTalk-type applications, you aren't worried about 
>precision pointing - even if a small amount of play does develop over 
>the years, who cares?
>Moonbounce is where precision pointing really does matter... and even 
>there, plastic bearing faces have been used very successfully. W5UN used 
>teflon very successfully for the bearing surfaces of his "Mighty Big 
>Array" - the one that was rotated by a motorized truck chassis on a 
>circular track. Teflon is notorious for creeping under load, but W5UN 
>took care to spread the loads over very large bearing faces. Inspired by 
>Dave's description in QST, I used pipe flanges faced with 1/8-in teflon 
>sheet for my own much smaller array. It had extremely unbalanced 
>sideways loading, but it worked fine with no evidence of creep or play 
>developing over 10+ years.
>73 from Ian G/GM3SEK
>See:  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


See:  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

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