You are correct about the elongation of holes in aluminum. It will take
less time in aluminum than steel but it will still happen in steel with a
large load. Now if aluminum to aluminum is properly clamped together under
compression, rather than pinning then you generally have no problems. As
evidence, I have had a 6 element 20 and a 3 element full size 40 on a
2-1/2" aluminum mast for approximately 20 years!
Pinning is not the preferred way to couple joints, (sometimes it is the
easiest and quickest way) but using a machined coupler is one of the best
ways to go. As evidence in above 20/40 antenna situation, neither antenna
nor mast to rotator is pinned and they have never slipped!
Personally I don't like steel. I always use aluminum if possible, it's
lighter and doesn't rust albeit it isn't as strong size to size.
I think we've had this discussion before and I still think you are short
changing aluminum masts.
> -----Original Message-----
> From: firstname.lastname@example.org
> [mailto:email@example.com]On Behalf Of K7LXC@aol.com
> Sent: Saturday, April 21, 2001 10:11 AM
> To: firstname.lastname@example.org; email@example.com
> Subject: Re: [TowerTalk] Lower Mast Question Again
> In a message dated 4/20/01 1:19:24 PM Pacific Daylight Time,
> > Rotational stress will work harden aluminum more than you might
> > guess.
> You better believe it. Rotational torque will elongate any
> hole with a
> bolt thru it. With an array your size, the aluminum mast will
> have a short
> service life.
> For anyone putting more than one antenna on a mast, one way
> to somewhat
> minimize the total rotation torque is to stagger antennas on both
> sides of
> the mast - i.e.. first antenna boom on the right, second antenna
> boom on the
> left, etc. This will lower the total mast torque and stresses
> everywhere -
> rotator, rotator plate, tower, guys, etc.
> Anyone who doesn't believe this will work hasn't read the articles by
> Dick Weber, K5IU, PE.
> Cheers, Steve K7LXC
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