Refinish options for etched aluminium? - Page 1
Forum section: electronics / general

author: brokenbones
author_rank: Newbie
timestamp: April 05, 2020, 05:27:59 am
content: I have an aluminum chassis with an etched face. What are my options to cover up or remove the etching? I'm repurposing the chassis for another project and I'd like to remove the lettering on the faceplate. Is it possible to paint over the etching without the lines bleeding through? Any ideas or tips would be appreciated.TIA

author: SeanB
author_rank: Super Contributor
timestamp: April 05, 2020, 09:59:53 am
content: If it is anodised then simply use a solution of NaOH solution ( alkali drain cleaner flakes) in warm water, and dip the plate in it. will strip the anodising off is seconds, taking the lettering with it in most cases, and if it is a coloured anodising it will be stripped as well.Caution, use gloves, do in a non corrodable plastic bowl, and dilute the resulting solution with at least 10 times the volume of water before you dump it down a drain after use, where it will also clean the drain out. This will dissolve skin, and turn fats (you, under the skin) into a soap, so do not splash it around, and have a large bucket of water handy to dump the object in after stripping, and to use on yourself if you get a drop on your skin. Adding the flakes to the water creates a lot of heat, so start with water barely under skin warm, it will be a lot hotter afterwards. Use 2 tablespoons to a litre of water, will be plenty strong enough.

author: Gyro
author_rank: Super Contributor
timestamp: April 05, 2020, 01:16:09 pm
content: Another Caution... if you do the NaOH trick, then do itoutside!I once etched a panel like that in the utility room. It bubbled as you'd expect, but when I tried to breath in, my throat locked solid and I literally couldn't get a breath. I had to quickly evacuate the family through the front door, take a deep breath, rush back in and chuck the panel out of the back door into the garden!I've no idea what the reaction was, maybe it was just NaOH bubbling (boiling?) off in suspension. Maybe it was just a fluke, but with two young kids in the house, it scared the hell out of me!

author: Nusa
author_rank: Super Contributor
timestamp: April 05, 2020, 03:54:24 pm
content: This is one of those pictures is worth a thousand words thing, rather than taking the effort of throwing out ideas that aren't going to work in your situation.

author: brokenbones
author_rank: Newbie
timestamp: April 05, 2020, 04:46:41 pm
content: Here are the pics that i've posted on another forum. There has been some debate on whether or not it's anodized or polished. I did some digging online on how to test for each surface...."An anodized surface will show essentially infinite ohms" and "if there is continuity, there is no coating"Also..."Scrape a penny across an unobtrusive portion of the metal.If the penny is able to scratch the finish, the material is polished aluminum. If the penny leaves a streak of copper on the item, then the surface is harder than the copper and the piece has been anodized."The results of these tests were that the penny did not leave copper, only a scratch. Continuity and an ohm reading other than infinite required swapping my 'needle point' leads for a set of thicker alligator clip leads. A small amount of pressure had to be put on the test points in order to get these results. I still don't know if I should use the caustic removal approach or just sand it. Any thoughts?

author: KL27x
author_rank: Super Contributor
timestamp: April 05, 2020, 05:09:36 pm
content: Sandpaper. 220 then 400. I would use the aforementioned sponge or just a finger-platen and focus on the lettering. Like painting, you want to blend it in over a larger area. Then paper over a large diameter dowel or a Bic lighter to blend in the edges without rounding them over.400 grit is fast, it hides imperfections, and it looks amazing on most metals.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 05, 2020, 05:12:44 pm
content: The caustic solution can etch aluminum quite easy, but the printed labels my protect the surface. I would go for sanding with relatively fine paper. Before that one could try to remove the paint part with acetone or maybe heat.The bubbling during NaOH etching are mainly hydrogen. The nasty smell / fog is likely aerosol forming, that can be a problem.A difficulty is that if the etching is fast, the solution will heat up quite a bit and than get even faster and hotter. So once fast it is hard to control. There is also some non soluble residue (e.g. mixed Al-Na-OH) and often uneven etching. The usual aluminum is not pure but one of many different alloys. So not at aluminum behaves the same.Sometimes on can just flip over the front-panel, having the old label on the inside.

author: brokenbones
author_rank: Newbie
timestamp: April 05, 2020, 05:18:23 pm
content: I picked up some 400 through 3000 grit increments and some polish. I want to see my reflection after it's done. Should I worry about sealing the surface? The unit will be indoors most of it's life.

author: KL27x
author_rank: Super Contributor
timestamp: April 05, 2020, 06:00:29 pm
content: No, I wouldn't bother sealing it. A thin layer of aluminum oxide will form, but it will be largely invisible.If you want a mirror, that's easy on aluminum. I would only bother with 1000 grit paper, then switch to a piece of leather and some buffing compounds. You want a couple different kinds for speed, ideally. A coarser black one and the fine green stuff. And if you have rubber gloves, this is the time to wear them, else your hands will be black for the next 30 hours.But you will still need at least 400 if not 220 grit, in my estimation, to efficiently dig the etching out and to get it blended in. Do that part right, then you can worry about how mirrory you want it. Aluminum polishes up like lightning.If you want a perfectly flat mirror, then you would probably need to lap it.

author: coppercone2
author_rank: Super Contributor
timestamp: April 06, 2020, 01:57:17 am
content: when I polish aluminum I go from 220-3000 (up to 400 on the oscillating sander then the higher grits go on the vibratory sander. Then I use 'mothers aluminum polish'. This is ALOT of work though. If you leave it at a modest level (1500 or so) with the vibratory sander, it looks kinda cool on big surfaces (patchy). Only reason I use the vibratory sander is because they don't seem to sell hook and loop sand paper locally for higher grits then 400, but I HIGHLY recommend the new diablo brand sand paper 'net' pads. They are like 2x as expensive but the dust goes through the sand pad into the extractor.. its great. They make em from like 80 to 400 IIRC.Dealing with hard anodized aluminum is a PITA mechanically. I have not tried it with chemicals but I had a really nasty scratched up hard anodized aluminum surface and I sanded it down. Took forever, felt like it was destroying sand paper, uneven sanding, unpleasant etc.Alumninum is weird because I have seen people just skip alot of the sand paper steps and go crazy on a buffing wheel and it gets similarly sparkling results. But, I try to avoid buff polishing because it makes plumes of dust. Like for manifolds.. people just seem to take them dirty and put them right on the wheel after some wire brushing to get them shiny, but its like hours on the buffing wheel.(the actual setup that you SHOULD (*if you are a billionaire*) have is insane, think gloves+apron integrated into each other with giant dust extractors behind the wheel sucking tons of air). I try not to use it and shower immediately since my setup is ghetto. I think 'real' machine shops that do alot of work have their own lowly paid polishing guys + dedicated room for polishing, since its such a nasty operation on the wheel if done dry (which is why I like mag+aluminum polishing compound, since its a smear). My shops is trashed after heavy polishing wheel use.. if its nice I try to take it outside on a stone wall to work there.Keep in mind if you are serious about polishing, there are three (basic that I know of) steps to it that use sisal, stitched and loose wheel, depending on removal rate. Sisal wheels are very aggressive, while the loose wheel is dainty.. and they are compound, material and surface finish specific. Like, I don't think it makes sense to use black polishing compound (very hard) on a loose buff wheel, and its only recommended to use it with hard sisal (the stuff ropes are made from).. harbor freight even sells like 6 compounds.. plastic, non ferrous, hard clean, medium clean, standard jewelers rogue, etc.Where to go from sand paper to polishing depends on geometry, surface finish and probably other factors. I feel like you would need to do it alot to know what works best. When I bearly knew about the tools, I got a near perfect finish on a damaged multimeter with just tooth paste. I almost feel like you might want to sand, then polish to know where to sand, then polish again with some things (maybe its just me). I noticed this with copper structures, you can reduce the work load alot if you just do a light polish first, clean, to find trouble spots, then work on them with more aggressive methods (sand, different wheel, different compound) to match the finish, rather then to do the whole thing (its a crazy amount of work to make a nice finish on a big object). It's also EXTREMELY boring. I feel like I am going crazy if I just try to follow a step set and doing at least some unnecessary work. And you also need experience to know the wheel speed and pressure to apply, when to clean, etc..easy on paper and cheap on first thought but its neither if you want to do a reasonable amount of work.Not to mention, it hurts your hands/fingers. At this point I cringe at the thought of scrubbing stuff. On the plus side, after you polish and clean a bunch of tools, chassis, car.. you really start to be careful about damaging equipment because you put so much work into it.. usually means you work a bit safer since you clear the area you are working in and stuff like that (not because you care for personal safety of course, just because something might get... SCRATCHED!The worst is thinking 'yeah thats easy to fix, I will just bang on it a bunch and fix it on a rainy day (teenage you). Well that day is going to rain with tears.I swear standing infront of that wheel covered in dust messes with your head after a while.On an interesting note, I wonder if someone has a particulate sensor and can take a measurement in a shop after polishing occurs. I have a feeling its very bad.Also, consider using a sharpie or something to mark up stuff thats not totally trashed so you reduce your work load.And for bare aluminum, the mothers mag + aluminum polish compound has some protectant in it (silicone based IIRC), so if its your last step it should be some what protected. I bought proxxon tools on eBay that have aluminum base with some kind of stains, I just used the mag/al polish on it and it restored it to the holographic status (its fly cut, so its not a 'mirror', more like a hologram.. but it would be mirror like if it was ground/lapped/etc).For using wet polishing compounds like that, I recommend the milwakee polisher/sander tool that runs on batteries with the side grip. I think you will find doing it with a drill will PISS YOU OFF SEVRELELY. Die grinder/polisher/etc are GODSENDS. I only ever use the drill to do something if I need an extension rod.

author: coppercone2
author_rank: Super Contributor
timestamp: April 06, 2020, 02:39:30 am
content: https://www.northerntool.com/shop/tools/product_200704090_200704090?cm_mmc=Google-pla&utm_source=Google_PLA&utm_medium=Power%20Tools%20%3E%20Polishers%20%26%20Sanders%20%2B%20Accessories&utm_campaign=Milwaukee&utm_content=63551&gclid=EAIaIQobChMI2vK4neLS6AIVEODICh1Gogo9EAQYAyABEgL7G_D_BwE(use the sponge)https://www.walmart.com/ip/Mothers-Mag-Aluminum-Metal-Polish-5-oz/20896445?wmlspartner=wlpa&selectedSellerId=101002903&adid=22222222227000000000&wl0=&wl1=g&wl2=c&wl3=42423897272&wl4=pla-51320962143&wl5=9004235&wl6=&wl7=&wl8=&wl9=pla&wl10=136582778&wl11=online&wl12=20896445&veh=sem&gclid=EAIaIQobChMI_bGe7eLS6AIVBeXICh0HVwQ3EAQYASABEgKq7vD_BwEGreat for aluminum with wet polish, or doing things like table tops that are laquered. Keep in mind if you want to do carshow work, its considered primitive, but I have not gone into doing hard core car surface work.. seems like you need a rotary tool, a dual action buffer and a random orbital for the different steps to keep the car people happy. But I think for aluminum, just the rotary is fine. And its also useful as fuck. I don't go too hard on paint because it gets trashed too easily by solvents in the shop, so its almost disposable.For a nice car (touch up, few years old, clearcoat in good condition):https://www.maxtool.com/products/makita-xop02z-18v-lxt-5-6-inch-dual-action-random-orbit-polisher-bare-tool?gclid=EAIaIQobChMIh_LekOPS6AIVRF8NCh1ntAaaEAQYASABEgKhPvD_BwEFor a fucked up car, or after a fresh clear coat:https://www.homedepot.com/p/Milwaukee-M18-FUEL-18-Volt-Lithium-Ion-Brushless-Cordless-7-in-Variable-Speed-Polisher-Tool-Only-2738-20/207163625?mtc=Shopping-B-F_D25T-G-D25T-25_9_PORTABLE_POWER-Multi-NA-Feed-PLA-NA-NA-PortablePower_PLA&cm_mmc=Shopping-B-F_D25T-G-D25T-25_9_PORTABLE_POWER-Multi-NA-Feed-PLA-NA-NA-PortablePower_PLA-71700000034127218-58700003933021540-92700051577220114&gclid=EAIaIQobChMIr6uAn-PS6AIVBj0MCh2Krw1eEAQYASABEgKXvPD_BwE&gclsrc=aw.ds(you need both tools)(the work will be slow if you use the random orbital with coarse grits on a really worn paint job). Not cheap, you would need to do like 3 cars to justify owning these tools IMO. But thats off topic since this is about metal thankfully.Oh yea, then you might want another weak LIGHT tool for doing wax work ,since your hands will be falling off at this point if you do a car. Shitty job really, you need to get it done fast so it does not get dirty and scratched up before you finish and put the protective wax on.. so it helps to have everything to make it done as fast as possible without killing yourself with heavy tools if you don't need heavy tools.

author: coppercone2
author_rank: Super Contributor
timestamp: April 06, 2020, 03:26:32 am
content: also keep in mind if you polish bare metal, fingerprints could be an issue. The chassis is designed that way for a reason, the scratches hide faults. I find the only shiny thing that stays looking good in my house.. is the ceiling chrome plated light fixture cover. People actually specify consumer surface finishes (complete with guidelines). With perfection ANYTHING stands out.It looks good but I think there is a reason test equipment manufacturers don't sell stuff like that, because it will get trashed during normal use in a lab.I am guessing out of curiosity you want to make some kind of fancy AV equipment for a music room or something? If you TRULY wanted it to stay mirrored forever, you would probably need to put an actual mirror with cutouts (like a good quality glass mirror).And keep in mind if you sell bare aluminum that looks nice, you need cleaning guidelines on what not to do. Like IIRC my shower door got attacked by 'kaboom' cleaner.. soap only on that.