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Old 1st Jun 2017, 1:06 pm   #1
MrBungle
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Default Cleaning up cast aluminium

I've just obtained an HP 427A voltmeter and it's rather dirty and grubby. Works fine however.

How should I go about cleaning up the exposed aluminium cast parts on this unit?
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Old 1st Jun 2017, 1:33 pm   #2
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Default Re: Cleaning up cast aluminium

Elbow grease, rub down with wet and dry (used wet) and then polish with Brasso/Autoglym, there are no shortcuts.
 
Old 1st Jun 2017, 1:52 pm   #3
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Default Re: Cleaning up cast aluminium

I'm good with that - there is satisfaction in not taking shortcuts

Thank you!
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Old 1st Jun 2017, 2:20 pm   #4
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Default Re: Cleaning up cast aluminium

Are the parts easily removable? If so a local polishing company would save a lot of time.
 
Old 1st Jun 2017, 2:33 pm   #5
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Default Re: Cleaning up cast aluminium

Yes they are. The whole thing is a sandwich with two cast end blocks. Can undo a few screws and they come right off. The whole thing is gloriously well made if I'm honest.

Picture of a slightly less cruddy looking one:

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I'll do it myself I think. It's only the outer edges that need tidying up - the rest of the cast sides is fine stock.

I think I'll do a thread on this restoration when I'm done.

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Old 1st Jun 2017, 4:29 pm   #6
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Default Re: Cleaning up cast aluminium

I saw this thread on the restoration of a HP 3410A on the eevblog forum a while ago, it shows how you can get these meters to look as good as new, link below for the post on cleaning the side frames.

http://www.eevblog.com/forum/testgea...995/#msg433995

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Old 1st Jun 2017, 6:41 pm   #7
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Default Re: Cleaning up cast aluminium

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Originally Posted by factory View Post
That's well worth reading; the guy seems like a very competent and enthusiastic restorer.

His approach to dealing with rotary switches is interesting; "The switches were treated with Deoxit D100L and cycled thoroughly. Then washed with electronic cleaner spray and blown out with compressed air. This shows final application of Deoxit G100L to lube then thoroughly cycled and blowing off any excess".

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Old 1st Jun 2017, 7:34 pm   #8
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Default Re: Cleaning up cast aluminium

I've done the switches. 30v range and above were dead. WD40 contact cleaner (not normal WD40).

Thanks for the link above to the other restoration - looks good!
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Old 1st Jun 2017, 7:54 pm   #9
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Default Re: Cleaning up cast aluminium

A polishing mop on a bench grinder (or, failing that, a pistol drill) saves a lot of time and effort. For good results, the Al needs polishing before NaOH treatment, or the flaws will still show.
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Old 1st Jun 2017, 8:29 pm   #10
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Default Re: Cleaning up cast aluminium

I've got a dremel and elbow grease
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Old 3rd Jun 2017, 2:13 pm   #11
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Default Re: Cleaning up cast aluminium

Dseymo1 is correct about using caustic soda: Any scratch seems to be 'etched down' along with the surface so is still visible after the process. I used to do front panels with caustic soda years ago but if the surface was not perfect before I started I would clean it with a mop and Autosol for a shine (or wire wool or linish it for an 'all over scratch'), so that the finish after etching was uniform.
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Old 15th Jun 2017, 1:46 pm   #12
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Default Re: Cleaning up cast aluminium

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Originally Posted by Bazz4CQJ View Post
Quote:
Originally Posted by factory View Post
That's well worth reading; the guy seems like a very competent and enthusiastic restorer.
He certainly is and while the end result is impressive, I ask myself why so perfectionist? Surely getting a piece of test-gear working properly and cleaning the worst of the muck off it is enough?

I was interested in his way of cleaning permanent marker off vinyl. He used toluene to remove the permanent marker, followed by something called "Mother's Back to Black". I have a plastic front-cover on a Tektronix 466 'scope which has been written on with permanent marker. The toluene treatment doesn't damage the plastic, unlike some other solvents, but there is still evidence of the marking. I think this is due to the fact that the plastic under the permanent marker has not been affected by light/oxidation/whatever, while that not written on has done so. I suspect that the use of "Back to Black" is for a similar reason, but I can't find a source of this product in the UK. I have tried STP "Son of a Gun" which is used for restoring plastic items on cars (It works on the black rubber bumpers and other plastic bits on my MGB). This has made some improvement, but the markings are still evident, unlike the vinyl in the post. Does anyone know if "Mother's Back to Black" is available anywhere in the UK, or should I just persist with "Son of a Gun"?
Colin.
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Old 15th Jun 2017, 2:09 pm   #13
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Default Re: Cleaning up cast aluminium

I've cleaned up a few Tek scope covers. I've never got one uniformly clean.

This reminded me to post back. I cleaned it up, ignoring the pitting for now and have left it in reasonable condition. To be honest I got it calibrated and it's really 100% spot on so I'm not intending on dismantling it any further.

It's doing sterling work with a homebrew RF probe at the moment.

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Edit: finding this excellent little meter does have a downside though; they do lots of cute little bits of test gear in the same form factor. This may turn into a collection if I can get them past SWMBO.

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Old 15th Jun 2017, 3:44 pm   #14
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This may turn into a collection if I can get them past SWMBO
Where there is a will... Slightly back on topic, if only recording media where as stable as stains on PVC.
 
Old 16th Jun 2017, 8:40 pm   #15
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Default Re: Cleaning up cast aluminium

Mother's Back to Black is available via eBay. I suspect that it's mostly silicone oil, like most of these things.
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