[K4RY] Did the antenna rotor get examined?

[John Klingelhoeffer]

As I mentioned in my earlier email with the pictures, I completely agree
that stainless steel U bolts and other fasteners should replace what is now
in place, as well as replacing the boom to mast plate.  I would also
replace anything that is rusted.

Mosley likely has replacements for all of this, since the beam is still
manufactured, and most hams now demand stainless steel fasteners.  The boom
to mast plate will be thick aluminum plate. If they do not have SS
fasteners available, ask them for all the sizes needed.

Opelika Bolt and Nut will either have the SS fasteners, or be able to order
them for you.  McMaster.com also works if you are not a brick and mortar
type of person.  Beware, though, that I just looked for a bunch of U bolts
at McMaster and they did not have anything close enough to use, which
surprised me.  I'm redrilling some antenna booms because of that.

Please remember SS lockwashers, too.  This is a vibration environment.  SS
locknuts (flex-lock, *not Nylon insert*) also work well.

73

John...
WB4LNM









On Fri, Oct 23, 2015 at 2:16 PM, Kris Kirby <kris at catonic.us> wrote:

>
> I looked at these pictures and noticed a few things I want to point out.
> Far be it for me to criticize the choices that one makes on installation
> and the age of the hardware...
>
> Anything with rust on it now is likely to be non-galvanized steel, or
> galvanized steel that is approaching the end of it's useful life. If the
> rusted parts are loosened, it's likely they will shear and not be useful
> for replacement. Further, the assembly shows signs of a loose shackle at
> the top, so it would be wise to find a way to reinforce that part,
> perhaps with a set screw into the mast itself. However, that will just
> work as a shear pin in high winds, so it would be wise to calculate out
> appropriate values. It's possible to replace the hardware up there with
> stainless steel hardware, which can be reused, but the stainless has to
> be sized appropriately and a torque wrench should probably be used to
> prevent galling the threads of those parts.
>
> In the case where previous records have been lost as to the construction
> of various pieces and thier sources, it may be a better idea to
> completely replace with materials of known source and quality. This is
> quite an engineering challenge as T6160 aluminum has certain costs,
> benefits, and kips limits and 316 stainless has other limits and tends
> to develop stress cracks as metal fatigue over time. Titanium is pretty
> hard to get, unless you know of a source for good, space-rated surplus
> structural tubing.
>
> IANAME, however.
>
> Then you get into issues with grounding and dissimilar metals, where all
> the copper must interface with stainless before it interfaces with
> aluminum or any other sort of joint.
>
> In general, "standard" steel is going to come apart at 10+ years, Home
> Depot zinc is going to come apart a little bit longer, galvanized a
> little bit longer; heavy, hot-dipped galvanized a little bit longer, and
> stainless will be reusable at X number of years provided the threads
> aren't galled or it's been overloaded. The time frames shorten when you
> have corrosive environments like Birmingham's air used to be before some
> of the steel factories shut down.
>
> Also, RG-393 jumpers tend to survive corrosive environments such as
> power plant smoke stacks, because the jackets are pretty resistant to
> that sort of thing.
>
> --
> Kris Kirby, KE4AHR
> Disinformation Architect
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