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Author Topic: Tarnished Aluminium Chassis  (Read 547 times)

G3EDM

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Tarnished Aluminium Chassis
« on: June 14, 2021, 11:38:02 AM »

Yes, I'm spelling it the British way now. See below for picture of the oxidation and dust that has become engrained on the chassis in my homebrew projects, most of them built around seven years ago. The ARRL building instructions did say to dip the thing in bleach, and then coat the outside with protective acrylic spray, before mounting the components, but I never bothered.

I can hardly do the "dipping" procedure, now that those chassis are stuffed with components. Googling around, I find all sorts of recipes for liquids you can rub in to clean aluminium, often involving vinegar. Another piece of advice, found in those old ARRL books, is to use very fine sandpaper (fine emery paper) and brush "in the direction of the grain". So far, the only thing I have tried is "dust cloth and elbow grease" but this has no impact at all.

Advice? Not at all urgent, it is a purely cosmetic issue that has no impact on the operation of the station.



Edited to add: This seems to have coincided with my move from the bracing, and very dry, northeast USA to damp England.

73 de Martin, KB1WSY
« Last Edit: June 14, 2021, 11:41:48 AM by KB1WSY »
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AJ4SN

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Re: Tarnished Aluminium Chassis
« Reply #1 on: June 14, 2021, 12:36:37 PM »

You can try a piece of very fine sandpaper wrapped around a small block of wood. Only sand in one direction -- very important -- and you will very quickly have a nice brushed aluminium look. Check out my QRZ page for examples. I

Stan
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G3EDM

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Re: Tarnished Aluminium Chassis
« Reply #2 on: June 14, 2021, 12:46:51 PM »

You can try a piece of very fine sandpaper wrapped around a small block of wood. Only sand in one direction -- very important -- and you will very quickly have a nice brushed aluminium look.

Thanks. Do you then spray with acrylic protector? I am thinking it might be worth it, although I would then have to be careful to remove or shield the dials, meters, sockets and so forth. (Edited to add: But I'm pretty bad at using sprays, so I'd be quite worried about streaking, bubbles and so forth, and once that happens, you have to live with it for ever.)

I also remember some magic thing I used back in America to remove blemishes from my car's bodywork. I think it was called "rubbing compound" which is basically liquid sandpaper. You just rubbed it on with a cloth I think.

73 de Martin, KB1WSY
« Last Edit: June 14, 2021, 12:55:07 PM by KB1WSY »
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W1RKW

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Re: Tarnished Aluminium Chassis
« Reply #3 on: June 14, 2021, 01:48:04 PM »

rubbing compound or polishing compound.  Maybe a scotch brite pad initially followed by the compound.
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W7CXC

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Re: Tarnished Aluminium Chassis
« Reply #4 on: June 14, 2021, 08:53:15 PM »

Martin
They sell a product at NAPA used for cleaning up and restoring aluminum wheels. Cant remember name. Mabey aluma-brite?  It contains ,I believe, Phosphoric Acid and works real well. Then coat with clear Krylon. Might be a bit harsh for your use though. Scotch Brite then rubbing compound sounds good. David
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AC9QC

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Re: Tarnished Aluminium Chassis
« Reply #5 on: June 15, 2021, 04:44:16 AM »

Mothers?
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G3EDM

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Re: Tarnished Aluminium Chassis
« Reply #6 on: June 15, 2021, 05:10:12 AM »

Thanks for the advice everyone. I won't be working on this for a while but it's good to have pointers when I get to it!

73 de Martin, KB1WSY (for now)
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G3EDM

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Re: Tarnished Aluminium Chassis
« Reply #7 on: June 15, 2021, 12:11:17 PM »

As an attempted quick fix for the time being, I gently scrubbed the sample chassis with a scouring sponge (UK equivalent of American Scotch-Brite) and a bit of dish-washing detergent. As you can see from the photo below, there is a major improvement. However, and you cannot see this on the photo, there is now an uneven patina: the areas I scrubbed a bit harder (to get rid of spots) came out duller than the rest. I am sure hope I can fix this in the future with some very careful fine-sandpaper (or rubbing compound) work. That will be later....

I only scrubbed in one direction (up-down, in terms of the photo) so I am not sure where all those whirlygigs in the photo came from. They were probably there all along.



73 de Martin, KB1WSY
« Last Edit: June 15, 2021, 12:17:59 PM by KB1WSY »
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K3UIM

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Re: Tarnished Aluminium Chassis
« Reply #8 on: June 15, 2021, 02:32:54 PM »

Martin,

If it was my project I would disassemble it and give it a coat or two of "hammered" black and finish up with a clear coat.

Of course, I have no idea of the inner workings, or I wouldn't even consider it! The problem perhaps being the time element involved. LOL

Just a thought, assuming that you're much younger than me, with the time to do it . Hi,

Charlie
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Charlie. K3UIM
Where you are: I was!
Where I am: You will be!
So be nice to us old fogies!!

G3EDM

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Re: Tarnished Aluminium Chassis
« Reply #9 on: June 15, 2021, 11:43:34 PM »

Martin,

If it was my project I would disassemble it and give it a coat or two of "hammered" black and finish up with a clear coat.

Of course, I have no idea of the inner workings, or I wouldn't even consider it! The problem perhaps being the time element involved. LOL

Just a thought, assuming that you're much younger than me, with the time to do it . Hi,

Charlie

Thanks Charlie. I have considered the option of disassembly, although I would keep the plain aluminium finish but this time, do the proper finishing (dip in cleaning solution, then spray with Krylon) as recommended in the ARRL books. This would be quite easy to do with the unit in the photographs, which is a very basic transmit/receive switch. However, if you take (for example) my transmitter, disassembly would be a major task, reversing the many hours that went into building it in the first place. And then of course reassembly afterwards.

The only surfaces that are substantially damaged are the top plates or the tops of cabinets. Anything vertically arranged, such as front panels and the sides of chassis, still looks good. So I think the plan will be to try to get those top surfaces back to their shiny, unblemished state. Then, protect the tube sockets, transformers, meters and dials with tape, and spray the exposed surfaces with some kind of protective coat. Because I am a perfectionist, that might need to be preceded by a proper labeling of the front panels (I have the software and the electric laminator for that) prior to spraying. (Although there is a school of thought that homebrewed panels should not be labeled, because the builder doesn't need it. My gear is simple enough that I don't need labels!)

Something for later....

I suppose this also argues for "dust covers" on equipment when it is not in use.... The fact that it is the top surfaces that are worst affected probably points in that direction.

Edited to add: I do think the English climate is a factor. This gear was out in the open in my American shack for about four years after it was built, and still looked "as new". But after three years in southeast England, the tarnish is well established.

73 de Martin, KB1WSY
« Last Edit: June 15, 2021, 11:47:55 PM by KB1WSY »
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K6BSU

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Re: Tarnished Aluminium Chassis
« Reply #10 on: June 16, 2021, 10:07:12 AM »

Once aluminum is tarnished, or "etched",  only mechanical removal of the surface works.  Sandpaper and water washing is the best way. 
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K3UIM

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Re: Tarnished Aluminium Chassis
« Reply #11 on: June 16, 2021, 11:36:01 AM »

Martin, " building the 65-watt (input) crystal- controlled "Low Cost Transmitter" from the 1963 edition of ARRL's "Understanding Amateur Radio."

WOW!! That was the bible(small b) that I and the local novices used back then. I believe it's also where we, several of us, converted our ARC-5's to 110 volt supplies. (I still have a copy!) We built several things from that book, especially the transmatch, which seemed like it could almost load up a coat hanger on 40. (Metal hanger, of course! LOL) Loved that book!

Charlie
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Charlie. K3UIM
Where you are: I was!
Where I am: You will be!
So be nice to us old fogies!!

KE0ZU

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Re: Tarnished Aluminium Chassis
« Reply #12 on: June 16, 2021, 08:38:34 PM »

You could also do something like what I often use on aluminium Chassis.   I sand the surface with a 100 grit random orbital sanding disc.

This finish technique is basically what Collins Radio often used on both military, commercial, and consumer products.   In the last pic you can easily see the difference between the two surfaces.
 






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Regards, Mike
https://mikeharrison.smugmug.com/
Pics and bold print are usually links.

K3UIM

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Re: Tarnished Aluminium Chassis
« Reply #13 on: June 17, 2021, 05:46:21 AM »

It took 78 years, but I've finally seen "perfection"! (And I'm a retired T&D maker.)  :'( ;D

Now the problem is that I feel like a "Novice builder"! LOL  ::)

Thanks for the pics. Beautiful, professional workmanship!!

Charlie
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Charlie. K3UIM
Where you are: I was!
Where I am: You will be!
So be nice to us old fogies!!

W1RKW

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Re: Tarnished Aluminium Chassis
« Reply #14 on: June 17, 2021, 06:19:16 AM »

Hey Mike/ZU,
I thought that bench looked familiar.  Whatcha building?
Bob
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