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Re: [TowerTalk] The RIGHT Stuff ( Not Humor ) - Epoxy Suggestion needed

To: Dennis Vernacchia <n6ki73@gmail.com>
Subject: Re: [TowerTalk] The RIGHT Stuff ( Not Humor ) - Epoxy Suggestion needed
From: "Roger (K8RI)" <K8RI-on-TowerTalk@tm.net>
Date: Sat, 11 Apr 2009 17:47:43 -0400
List-post: <towertalk@contesting.com">mailto:towertalk@contesting.com>

Dennis Vernacchia wrote:
> I have a semi ancient  440 mhZ old F9FT long boom Yagi for 440 MHz
> ( Many elements on a 10 or 12 foot boom )
>
> The Driven element which is a folded dipole has separated from it's cracked
> black plastic insulator
> and a piece of the insulator is MIA
>
> The insulator used to be molded right around the N connector feed point
> which the driven element is soldered to.
>
> What would be the best type of Epoxy I could buy at say, Home Depot or a Ace
> Hardware store that will
>   
If there's a marine store in the area, or possibly you can find it 
elsewhere, pick up a "West System" Epoxy Kit  and some mill fiber. If 
you can find a piece of mill fiber, just get a small piece of fiberglass 
cloth and cut into small 1/4" or smaller pieces.  These are easily 
separated into the individual fibers.  Start with a small batch of epoxy 
and mix in enough fibers to make a paste. (lots of fibers, a little 
epoxy)  It might take some practice to get it right, but a mill fiber 
mix is strong.  Be careful if you mix very much epoxy as this is an 
exothermic reaction when it cures. The cure time and speed at which it 
cures depends on the amount mixed. More means faster AND hotter and 
getting it on you during cure is like getting hot melt glue on you. 
Initial cure (when it gets too stiff to work as a paste) IIRC takes 
about 15 minutes but can vary widely with the above conditions as well 
as temperature (warmer means faster) 

No special techniques are required to make the patch or apply and shape 
the material but working with fiberglass and epoxy does take a little 
practice. Some of us take more practice than others<:-)).

Make sure the pieces to be repaired are clean and roughed a bit with 
sand paper.  I cut a piece/strip of plastic from the container that 
electrical tape comes in. Any good PE should work. I round the end and 
it makes a good tool by sanding to apply the material as well as shape 
it.  After the "fix" reaches full cure (about 24 hours, or less) you can 
grind, sand, or cut the patch.  One of the little high speed grinders 
works well as does a small sanding block.

REMEMBER this contains fiberglass which will be in the dust from working 
on the patch.  Wear a dust mask and do not breathe in any of the dust.  
Like working with fiberglass insulation its a good idea to change 
clothes after getting in the dust.
> adhere to the old ubiquitous type black plastic insulator AND the round
> flanged body of the N connector,
> for a temp repair til I can machine a new insultor ( Round-To-Its are
> getting scrcer around here ! )
>
>   
If you have the tools to machine a new insulator you might want to 
experiment and make a split mold to make a new, professional looking 
insulator.  DC4 or 5 compound, or even Johnson's spray wax or Carbuna 
wax make good mold release agents. 

One added thought: if you can get the pigment (as long as it's not 
carbon black) adding a little to the mix can even give a part that looks 
like the original.

One other thing to remember is fiberglass and epoxy is not strongly UV 
resistant so you might find some additives, or just give it a couple 
coats of clear Krylon after full cure.


73 and good luck,

Roger (K8RI)

> 73, Dennis N6KI
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