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Author Topic: Tarnished Aluminium Chassis  (Read 548 times)

G3EDM

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Re: Tarnished Aluminium Chassis
« Reply #15 on: June 17, 2021, 07:20:37 AM »

This time I tried very fine sandpaper (320 grade), fastened it to a sanding block, and gently rubbed, only in one direction (front to back of the chassis). The chassis is now very clean and untarnished, but I am not satisfied with the result, because of the visible striations. This will just have to go on the back burner for now as I bring my station up to scratch for first key-down soon.





Edited to add: This unit is easy to disassemble so I may, later on, attempt a more aggressive solution such as dipping the top of the chassis into one of those corrosive aluminium cleaning chemicals. That's how it was done in the old days....

73 de Martin, KB1WSY
« Last Edit: June 17, 2021, 07:27:36 AM by KB1WSY »
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KM1H

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Re: Tarnished Aluminium Chassis
« Reply #16 on: June 17, 2021, 08:30:56 AM »

What do the restoration specialists use when pulling WW2 aircraft out of the ocean. The Brits are pretty active in that area; unfortunately one of my favorites, the Mosquito, dont qualify
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G3EDM

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Re: Tarnished Aluminium Chassis
« Reply #17 on: June 17, 2021, 10:43:12 AM »

Meanwhile I tried a different tack with my receiver and transmitter. I carefully cleaned the entire surfaces with nothing more aggressive than moistened Q-tips, followed by gentle rubbing with a dust-cloth. It worked fine! (Earlier, I had tried a dust cloth only, and that had no effect.) I don't think that tactic would have worked on the transmit-receive switch (shown in the centre of this picture), as the tarnish and dust were harder to dislodge. For the time being, all's well!



73 de Martin, KB1WSY (for now)


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K6BSU

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Re: Tarnished Aluminium Chassis
« Reply #18 on: June 17, 2021, 04:51:46 PM »

KB1ESY.  Your 320 grit is too coarse.  You should follow up with 600A wet-or-dry, using water as lube.  If smoother finish is desired, switch to 1200A.  Best results are obtained using several finer grits.  Going to extra-fine in the beginning will work, but will take forever!
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G3EDM

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Re: Tarnished Aluminium Chassis
« Reply #19 on: June 18, 2021, 01:17:16 AM »

KB1ESY.  Your 320 grit is too coarse.  You should follow up with 600A wet-or-dry, using water as lube.  If smoother finish is desired, switch to 1200A.  Best results are obtained using several finer grits.  Going to extra-fine in the beginning will work, but will take forever!

Sounds good! I used 320 because it was the finest I had in the toolbox. Will order some finer grades and have a go.

Among other things, the sandpaper has largely removed the existing finish (the gentle, directional "grain" that these Bud chassis have when they are new). So I suppose the trick now is to use very fine sandpaper to eliminate what is left of that finish as well as smoothe out the striations caused by the 320-grade. There are currently two issues after my initial cleaning effort on the T/R switch: (1) striations caused, as you point out, by over-coarse sandpaper and (2) patches where a bit of the original Bud finish is still showing, and this contrasts with the nearby patches where it has been removed altogether.

I can see that using very fine sandpaper could take forever, but the patience would be well rewarded if the only other options were to either "live with it" or rebuild using a new Bud chassis!

Edited to add a question for BSU: Even with the very fine paper, should I continue to sand in only one direction? Or should the ultimate aim be an even finish with no visible directional grain, in which case I would assume a gentle rotary motion might be used at the end of the sanding process, with the very fine paper?

73 de Martin, KB1WSY
« Last Edit: June 18, 2021, 01:21:08 AM by KB1WSY »
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K6BSU

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Re: Tarnished Aluminium Chassis
« Reply #20 on: June 18, 2021, 08:45:01 AM »

As you work the finer-grit sandpaper, all scratches go away.  So it doesn't matter how you sand.  It is less work to sand in small circles.  If you want a high polish on aluminum, you can even progress to 2000 grit, followed by a polishing compound (from auto supply stores).
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KM1H

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Re: Tarnished Aluminium Chassis
« Reply #21 on: June 18, 2021, 12:34:36 PM »

Wow does that bring back memories of building street rods and custom cars with many coats of hand rubbed lacquer paint. I learned the skill including leading back in my HS days when my best friends dad and uncle owned the top auto body shop in town..Old World Swede perfectionists that had the patience to teach me when I worked part time, weekends, and vacations.

Carl
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W1RKW

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Re: Tarnished Aluminium Chassis
« Reply #22 on: June 18, 2021, 02:18:39 PM »

Martin, one of 2 things or both are happening. try cleaning the surface between sandings with 90% isopropyl alcohol.   I suspect  there are some residual oils on the surface which could come from handling. Clean again at the end.  Also keep in mind that aluminum oxidizes very fast.  So if you intend clear coat or paint the surface, hit it again with the alcohol then clear coat or paint it.  Cleaning with alcohol is a common practice when welding aluminum so cleanliness is important. 
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