Dull Aluminum

[MasPlan]

After turning the blanks, the aluminum separator's between the segments, are bright & shining; like I want.
However, when sanding (the blanks), to prep for the finish, the aluminum goes dull, like pewter, and I can't get it "bright" again, even sanding / polishing to 12K with the Micro Mesh.
What's causing this? Any help will be greatly appreciated.

 

[jttheclockman]

What type blank? wood and aluminum or acrylic and aluminum?? Are you sanding before MM?

 

[Bryguy]

Aluminum is a highly reactive metal. When you cut it, you expose fresh metal to the air and it will be shiny. It will very quickly oxidize to a dull grey. The only way to prevent that is to keep it away from oxygen. This can be done by anodizing, but I think it would be next to impossible in a segment. Good luck with it. I'd use a less reactive metal if I wanted shiny segments.

 

[KenB259]

You can't sand it. Just finish with your lathe tool of choice.

 

[calabrese55]

Aluminum is a highly reactive metal. When you cut it, you expose fresh metal to the air and it will be shiny. It will very quickly oxidize to a dull grey. The only way to prevent that is to keep it away from oxygen. This can be done by anodizing, but I think it would be next to impossible in a segment. Good luck with it. I'd use a less reactive metal if I wanted shiny segments.

Pure aluminum as opposed to an alloy of aluminum is especially prone to creating a passivation layer from oxygen contact. The attached article is just one that details the condition. https://www.clintonaluminum.com/passivating-stainless-steel-aluminum/
You best bet would be to polish it up again and get a coating immediately on the part to block the contact with oxygen.
Lacquer , shellack , car wax, clear enamel spray paint all could work
Here is a Google link to Aluminum polish products
https://www.google.com/search?client=opera&q=aluminum+polish&sourceid=opera&ie=UTF-8&oe=UTF-8

calabrese55

 

[leehljp]

After turning the blanks, the aluminum separator's between the segments, are bright & shining; like I want.
However, when sanding (the blanks), to prep for the finish, the aluminum goes dull, like pewter, and I can't get it "bright" again, even sanding / polishing to 12K bwith the Micro Mesh.
What's causing this? Any help will be greatly appreciated.

Your tool is cutting it with a fine edge. That is normal. Too course of sandpaper dulls it. In fact, it would take 800 or better to bring a shine back to the metal. It is a known fact and is practiced by a few here (me included) that even shiny CA can be dulled make the CA less "plasticy". That is done by not sanding with anything more than about 4000MM (MicroMesh).

This is also a process that a few understand or use as a regular practice - in which a good very sharp tool will leave a smoother surface than sandpaper in many instances. Smoother (shining) surface on metal such as aluminum or brass in segments when used with wood is the result of the sharp tool. I do segments with brass or aluminum rings often and intentionally do not sand after turning smooth because sanding will cause the brass or aluminum sanding dust to contaminate the wood's color next to the ring. And, I doing it this way, I still have a shiny metal.

 

[jttheclockman]

The reason I asked weather wood is involved or acrylic is because then the aluminum segments would react differently. It is easy to keep shine but need to go about it differently. With both sanding is a no no. Tool to finish is the way to go. With acrylic Shape with tool and then MM (polishing) will get you there. With wood, shape with tool and then CA and then finish and polish with MM. Here is a pen I did years ago and I still own and still looks great the same as when I first finished it. It is acrylic and aluminum segments. Still shiny. Has only been MM polished. I do not use it so not sure how it would look when acid from fingers would always touch it but I am sure a good coat of wax would take care of that.

 

[hooked]

The best method is to avoid sanding as mentioned, but I always sand a bit because I always see some imperfections. This stuff works well for me at the end of my sanding process with acrylic. It takes my aluminum rings from what you describe after sanding to looking great.

Only warning is that if you are using with unfinished wood, it can potentially stain. It starts out white but when it works into the metal it turns black. I use mostly acrylic so this polish works really well for me.

I use a cotton swab and carefully apply to my rings while the lathe is turning before I buff. Wipe off with the other end of the swab.

https://www.amazon.com/Mothers-05100-Mag-Aluminum-Polish/dp/B00068GEJM/ref=mp_s_a_1_2?adgrpid=58763364951&hvadid=274706781965&hvdev=m&hvlocint=9001878&hvlocphy=1008736&hvnetw=g&hvqmt=e&hvrand=17149762002373259331&hvtargid=kwd-308014999890&hydadcr=18952_9708216&keywords=mothers+mag+and+aluminum+polish&qid=1686899086&sr=8-2

 

[leehljp]

The best method is to avoid sanding as mentioned, but I always sand a bit because I always see some imperfections. This stuff works well for me at the end of my sanding process with acrylic. It takes my aluminum rings from what you describe after sanding to looking great.

Only warning is that if you are using with unfinished wood, it can potentially stain. It starts out white but when it works into the metal it turns black. I use mostly acrylic so this polish works really well for me.

"but I always sand a bit because I always see some imperfections." The tool is excellent at handling imperfections amd ; it just takes the confidence to use it.

The pen below is before I learned the finer points of finishing metal as John did, but have since learned from him (reading his posts). However, the pen below had the solder dots in it and those dots smeared like pencil lead when even touched with (SP) sand paper. Erasers and or alcohol or soap and water on a paper towel could not remove it. The solution for me was a very sharp scraper and light touches and high speed over the whole blank. Since SP is a No-No, I had to finish turning the wood with the scraper. So, what you see is a pen blank that was not touched by SP. Yes, smooth as a can be. Old time wood workers / furniture makers knew how to make smooth wood without sandpaper, they used scrapers. It does well and makes wood smooth, which is the same principle to use on segmented pen blanks with metal spacers or inserts.

30 Pieces of Silver

Elegant Beauty TI Gold Bloodwood, BOW, Holly core solder CA finish

www.penturners.org

I did build up enough CA (measured with calipers) so that when I got the CA round on the blank with my scraper, I did use the high number MM to finish and then polish. One does NOT want to sand through the CA to the wood on segments with metal that smears with sandpaper.

 

[MasPlan]

What type blank? wood and aluminum or acrylic and aluminum?? Are you sanding before MM?

Either & Both; I'm certain it's something I'm doing (or not doing).
Yes, my steps are sand after turning, apply the finish, (usually CA), then Micro Mesh, Polish & wax. No CA on the acrylic, but wet sand with MM, polish & wax.
I've tried different sources of aluminum (drink cans & store bought), & have the same result on each.

 

[MasPlan]

Thank You All for the advice: I'll try leaving the sandpaper for the furniture, templates & jigs!
You've all been very helpful!

 

[jttheclockman]

Well glad we could be of some help. If wood and aluminum then never sand before CA because you ruined the tooling ability that you get when just using turning tools to shape. CA will not let you polish it back to shine because you coated over aluminum. Acrylic and aluminum again just needs tooling to get to finish size and shape and should be able to go right to MM and this will allow you to shine aluminum back to a nice shine. Good luck.