[TowerTalk] Aluminum scoring

[Roger (K8RI)]

On 5/30/2010 6:23 PM, k3hx at juno.com wrote:
> OM,
>
> I use abrasive sponges from Harbor Freight. Use them dry as the adhesive used to hold the grits onto the sponge is pretty weak.
>
>    
I stick with the file as I don't want to take anything off other than 
the burrs and dirt.
File takes the burs off and a fine "ScotchBrite(TM) pad will take care 
of the dirt.
> While you are wandering around the Harbor Freight store or going through their catalog you may note a 1/2" wide belt sander.  Thing is a piece of junk.
>
> Also, I've used "Scotchbrite" abrasive discs such as you might find at an auto supply store that caters to body shops.  Tell the counter person what you want to do and they can recommend the proper grade of abrasive disc.
>
> As for the inside of the joining tube, I have used a sandpaper "flap wheel" on a long extention.  Or, you could ask the folks at the auto store for a cylinder hone.  The catch is that the cylinder hone will be pretty expensive.
It's also not very effective on an aluminum tube and particularly soft 
aluminum. The stones load up real quick and that pretty much ruins them. 
I'd much prefer the "flap wheel", or rather the cheap version of a strip 
of emery cloth through the slot in the rod.
A cylinder hone is just that, a hone. It's not designed to really remove 
a lot of metal.  It hones the cylinder walls with literally millions of 
fine scratches.  During break in, these scratches help the rings to wear 
and "seat in". The hone is just a set of 3 or 4 spring loaded polishing 
stones (same as those used for putting the finish on knife edges). They 
are meant to be used on an already smooth surface.
>    Many auto parts stores have a machine shop attendant to them, perhaps they have a used cylinder hone they can let go for cheap.
>    
Take a piece of 1/4" or 3/8" rod, with a hack saw, cut a slot in the end 
as deep as the sandpaper (prefer emery cloth) is wide. This makes for a 
very inexpensive "flap wheel". The problem is this approach removes more 
than just the burrs. If you use a coarse grit, use it sparingly and 
follow up with a fine grit to take out the deep scratches.

IF you clean the inside piece well and then coat it with either pentrox 
or never seize, when you put the thing back together put the inside 
piece in place by twisting it back and fourth as it goes in. The 
*should* clean off any burrs on the inside of the outer boom. If so 
inclined, take them back apart and using mineral spirits on shop towels 
(the cheap kind), clean the two tubes thoroughly.  Then recoat the inner 
tube and put a generous coat of never seize or pentrox just inside the 
boom. the two pieces should slide together easily. I've never found the 
need to clean and recoat a necessity.  This is not a place where 
precision is needed.

73

Roger (K8RI)
> I'm not a fan of using steel wool as the little threads can become embedded in the aluminum.
>
> To prevent future trouble getting things apart, I clean the smooth surface with 91% isopropyl alcohol and then apply a coat of ordinary automotive polish and then some anti-seize.
>
> 72,
>
> Tim
>
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