24 replies to this topic

[betacygni]

Has anyone successfully removed anodizing? I’ve seen some various internet articles and YouTube videos, but curious if anyone has any first hand experience (good or bad)? Any issues with aluminum long term discoloring without being anodized?

For the record I hope the red anodized part trend is short lived…

[wrvond]

I've not intentionally removed it, but I seem to have removed a bunch of it over the years - including a couple big scratches on the tailgate of my truck. It's been about five years and the exposed aluminum is still shiny.

[betacygni]

I've not intentionally removed it, but I seem to have removed a bunch of it over the years - including a couple big scratches on the tailgate of my truck. It's been about five years and the exposed aluminum is still shiny.

Good to know, as I also have an aluminum ford and hadn’t considered that!

[wrvond]

In another life I worked on torpedoes with red anodized screws (propellors). Occasionally I'd have to sand an area down to bare metal and then apply a cold anodizing finish and clear lacquer over that. I'm sure there's a chemical method for removal, but I suspect that would be rather hazardous. A sanding wheel (flapper) would probably work best.

Edited by wrvond, 30 January 2023 - 11:45 PM.

[siriusandthepup]

Anodizing is not a coating like paint, something totally separate from the original item.

 

It's an oxidation process of the parent material.

 

How do ya get it "off"? Abrasion to remove the layer of oxidation. In other words, you must do damage to the original item to get it off.

 

What is Anodizing?

 

When you have your mirror recoated with fresh aluminum - when you first receive it, it has a pure aluminum surface. Over the first few weeks, natural oxidation occurs to create a thin surface layer of aluminum oxide. A protective hard layer similar to sapphire. Anodizing does the same thing to aluminum parts - in a much accelerated and aggressive manner (with color added as a bonus!).

Edited by siriusandthepup, 31 January 2023 - 12:22 AM.

[photomagica]

Anodizing is a thin aluminum oxide coating that is actually part of the surface of the aluminum. It is generated by an electrochemical process. The aluminum oxide is porous so it can absorb dye - giving some great colors. Because the anodizing is actually part of the surface and is very chemically resistant, it needs to be machined or ground off, as others here have noted. 

 

A full, mil spec anodized coating is so thick and hard that it is difficult to grind off. After all, aluminum oxide is a common abrasive. It can quickly dull high speed steel lathe tools when machining it off. It is necessary to plunge the tool through the anodizing and essentially peel it off. I use a silicon carbide tool if I have to machine it off and it may even dull that kind of tool if I have to remove a lot.

 

When producing telescope parts, I either send them out for anodizing or have them epoxy powder coated if I can. 

 

There are various finishes that may be applied that mimic anodizing; alodyne coatings and various paints or lacquers, but none even come close to matching the durability of a good, hard anodizing job.

Best regards,

Bill

Edited by photomagica, 31 January 2023 - 12:25 AM.

[Jim in PA]

I remove anodizing by sanding followed by a trip to the blasting cabinet.  Once the oxidized layer is removed, aluminum is free to corrode.  So I don't like to leave it that way for long.  A quick spray coat of lacquer will help if leaving it "in the white" for a while.

 

When it comes to finishing smaller astronomy parts, after thoroughly re-blasting with oxide grit, then bead blasting, then degreasing...I will usually use a very flat epoxy coating such as Duracoat applied with an airbrush.  Larger parts I'll powder coat.  Very rarely do I use anodizing as a finish for astro gear, but that's just my personal preference.

[TOMDEY]

Al₂O₃ is a very hard oxide crystalline structure --- think of it as hard glass tenaciously adhering/bonded to the remaining metal beneath. Abrasion is the only practical way to remove it.    Tom

[TOMDEY]

Found this > looks like a rather nasty process --- but you might want to look into it. We did that at B&L... I actually did it did it as a summer worker back in 1964! I would dip baskets of parts into steaming Hot Caustic tubs and other chemicals with these big heavy rubber gloves on and rubber apron, mask, boots etc. etc. and huge blowers sucking the vapors away from me. When I splashed a miniscule few drops onto my clothing --- it immediately ate right through the fabric and burned my skin. So --- it can indeed be done chemically... but not exactly a home hobby kinda thing. I can only assume that inhaling even a bit of the vapor would send one straight to the ER.   Tom

 

 

"Sodium Hydroxide: Also known as caustic soda or lye (NaOH), it is the most common method for stripping anodized coating. The concentration of caustic soda is generally 2-10% of 50% liquid caustic soda by volume in water."

Edited by TOMDEY, 31 January 2023 - 01:09 AM.

[Jim in PA]

Most of the time, unless I have a very good reason...I will leave the anodized/oxidized layer in place when refinishing a part.  It doesn't hurt anything to leave it intact.  It serves as a very good anti-corrosion undercoat for epoxy-based coatings.  I'll just try to blend in any machining with grit and bead blasting to the area that I machined/modified.

 

This is one reason why I like to use epoxy based coatings on complex surfaces over powder coating.  I don't have to worry about conductivity.

[betacygni]

Hmmm not promising info. What about painting over top anodizing with spray paint? Perhaps I’ll just have to let function trump form, all the same color at night I suppose.

[NinePlanets]

Anodizing is a GREAT surface prep for paint on aluminum! The best! 

[Jim in PA]

Anodizing is a GREAT surface prep for paint on aluminum! The best! 

Just need to keep in mind that some finished anodized parts are clearcoated and that can be pretty slick.  So if you anodize it yourself and paint it, it's a great surface.  But if it's already been clearcoated, gotta deal with that.  I would carefully prep the part with scotchbrite, degrease, etc.

 

Edit: not all parts would be clearcoated...I've noticed some of my commercially made astro parts like dovetails are.

Edited by Jim in PA, 31 January 2023 - 09:32 AM.

[Philip Jodry]

Anodizing is not only porous aluminum depositing, it's a dye bath afterwards, to give a distinct beautiful finish to parts. The dye will fade in time, and can be renewed. Anodized parts have some extra corrosion resistance. The dye can be stripped and another color dipped. I love anodized stuff.

[photomagica]

Anodizing is not only porous aluminum depositing, it's a dye bath afterwards, to give a distinct beautiful finish to parts. The dye will fade in time, and can be renewed. Anodized parts have some extra corrosion resistance. The dye can be stripped and another color dipped. I love anodized stuff.

I love it too! It turns aluminum from this awful metal with a soft surface that easily corrodes into something durable and attractive. If the anodized surface has been sealed after the dye is applied - there are various ways of doing this ranging from boiling the part to wax, acrylic or epoxy coatings - then the part may be difficult or impossible to re-dye.

 

I've done anodizing but, as noted, it involves nasty chemicals, so I prefer to send it out. Also the professional anodizers are all set up to properly clean the part and achieve a thick, uniform coating. They typically have a good range of color dyes available as well. If you are interested in a do-it-yourself approach there was an excellent article in Home Shop Machinist or its companion publication Machinist's Workshop not too long ago. The author has found a way to use common poll maintenance chemicals which reduces the risk.

 

Anodizers typically have a minimum charge, in my case that is $50. It is costly to have one small part done. I try and wait until I have several parts.

Bill

[betacygni]

Found this video that makes it look pretty easy just using oven cleaner: https://m.youtube.co...h?v=YCZNbozXHbo

Little concerned he doesn’t show the completely stripped final product though. Might give it a try with a cheap item first.

[Polyphemos]

Found this video that makes it look pretty easy just using oven cleaner: https://m.youtube.co...h?v=YCZNbozXHbo

Little concerned he doesn’t show the completely stripped final product though. Might give it a try with a cheap item first.

Looks like it removed the dye, not the aluminum oxide.

[SteveG]

Has anyone successfully removed anodizing? I’ve seen some various internet articles and YouTube videos, but curious if anyone has any first hand experience (good or bad)? Any issues with aluminum long term discoloring without being anodized?

For the record I hope the red anodized part trend is short lived…

Just curious, what are you trying to fix?

[betacygni]

Just curious, what are you trying to fix?

Red anodizing that looks terrible, primarily on a finder shoe/handle. Only a $35 part so not too worried if I mess it up. Vanity I know, but it really clashes with the rest of the scope. I enjoy looking at my scopes as well as through them.

[luxo II]

Red anodizing that looks terrible, primarily on a finder shoe/handle. Only a $35 part so not too worried if I mess it up. Vanity I know, but it really clashes with the rest of the scope. I enjoy looking at my scopes as well as through them.

Forget it - buy a black one as you'll waste more trying to get it off.

[betacygni]

Forget it - buy a black one as you'll waste more trying to get it off.

Not available in black otherwise I would have.

[Philip Jodry]

One of the nicest aluminum sources for casting is soda can aluminum. It's actually 2 similar alloys for the lid and body. It's very resistant to corrosion and would make an excellent anodizing sacrificial cathode. Anodizing is extremely easy.

[SteveG]

Red anodizing that looks terrible, primarily on a finder shoe/handle. Only a $35 part so not too worried if I mess it up. Vanity I know, but it really clashes with the rest of the scope. I enjoy looking at my scopes as well as through them.

Got it. It's always fun to refinish or restore parts, even the simple ones.

[Philip Jodry]

Paint your red knob black and the next owner can strip the paint off.

[Mph100]

Been doing some diy anodizing had good results on smaller parts but not so much success on larger parts to strip the unsuccessful anodized layer plus the dye off because of blotchy results ive used sodium hydroxide with great success the warmer the solution the better