How would one polish an aluminum swing arm

[Dents]

I just bought an aluminum swing arm off eBay for 65 bucks including shipping. It's going to replace my old aluminum one I damaged by accidentally flipping my wheel spacer. Anyway I'd like to clean this new one up a bit before putting it on the bike. I don't want a blinged out version just a nice satin finish. Anyone got any tips to do it. I'll probably get my old one fixed and sell that one later. 

[DucNaked]

Buffing wheel and compound. And lots of elbow grease. Use a dustmask because things get messy. 

[scduc]

Not only will things get messy, but aluminum dust is associated with Alzheimer's

[RBX QB]

Not only will things get messy, but aluminum dust is associated with Alzheimer's.

The original actor playing Scarecrow in Wizard of Oz (Buddy Ebsen, if memory serves) had to drop out because the silver paint they were using was making him terribly ill. It was aluminum powder. I wish I knew as much about my job as I do about movie trivia.


+1 on a dust mask... and I'll raise you some decent gloves. Good winter project.

[Speeddog]

I've been told, by people that have polished theirs....
that the best way is to pay someone that has the equipment and experience to do it.

[booger]

shot-peen then anodize

increase the fatigue life and surface hardness at the same time

[Thuddds]

The cast areas will have to be sanded first, then polished.  Sand casting produces a rough texture that is nearly impossible to polish.  Sanding would likely start at a 100 grit and work progressively towards 1000 grit prior to polishing with compound.  

Machined and extruded surfaces are more uniform and can be polished easily with a wheel or ball.

Most aluminum parts are anodized from the factory, so the coating will have to be removed prior to polish. Anodizing can be removed with a caustic, or by light sanding with 400 grit wet/dry.

To achieve a satin finish, rather than a mirror finish, you will likely have to media-blast the aluminum.  Baking soda will leave a lighter, hazy finish much like satin.

It is best to clear-coat immediatly on completion of refinishing.  Aluminum oxidizes quickly.  Even more quickly with a textured finish. On this note, the clear coat can function as the satin finish following surface preparation, thus eliminating the need for polishing.  Some automotive paint stores even sell a 2-part clearcoat in a rattle can in high gloss, semi gloss, and satin.

[Langanobob]

shot-peen then anodize

increase the fatigue life and surface hardness at the same time

I seem to remember from a previous wannabe airplane builder life that anodizing aluminum can dramatically decrease fatigue life.



But there may be more to this issue, things like this are rarely black and white.

Bob

[ducatiz]

The original actor playing Scarecrow in Wizard of Oz (Buddy Ebsen, if memory serves) had to drop out because the silver paint they were using was making him terribly ill. It was aluminum powder. I wish I knew as much about my job as I do about movie trivia.

and Buddy died at almost 100 years old with no Alzheimers.

it was an allergy

[booger]

I seem to remember from a previous wannabe airplane builder life that anodizing aluminum can dramatically decrease fatigue life.



But there may be more to this issue, things like this are rarely black and white.

Bob

I don't think I agree with that. Anodizing is a surface treatment. I cannot believe it affects the entire cross sectional area of an aluminum part. Shot peening increases strength. Both processes are commonly done to things like lightweight mountain bike parts, where that extra miniscule little bit of strength and surface durability is warmly welcomed on ridiculously lightened pieces.

Aviation itself is one thing that dramatically reduces fatigue life. Airplane parts don't last long. 

[ducatiz]

I don't think I agree with that. Anodizing is a surface treatment. I cannot believe it affects the entire cross sectional area of an aluminum part. Shot peening increases strength. Both processes are commonly done to things like lightweight mountain bike parts, where that extra miniscule little bit of strength and surface durability is warmly welcomed on ridiculously lightened pieces.

Aviation itself is one thing that dramatically reduces fatigue life. Airplane parts don't last long. 

hard anodizing makes the surface layer more brittle and relies on the substrate material for torsional strength. 

considering that machine gun parts from aluminum are hard anodized, i cannot say i accept that anodizing has any affect on strength at all.

[errazor]

I don't know if i agree or disagree, but i know that alot of a materials strength is in its outer surface. maybe hard anodizing is stronger?

[suzyj]

I seem to remember from a previous wannabe airplane builder life that anodizing aluminum can dramatically decrease fatigue life.



But there may be more to this issue, things like this are rarely black and white.

Bob

Decorative soft anodizing has little effect - hard anodizing creates a brittle surface from which cracks can propagate.  This is most commonly an issue with anodized bicycle rims - the hard anodized ones have a much shorter fatigue life than soft anodized ones.

[corey]

Not only will things get messy, but aluminum dust is associated with Alzheimer's.

The original actor playing Scarecrow in Wizard of Oz (Buddy Ebsen, if memory serves) had to drop out because the silver paint they were using was making him terribly ill. It was aluminum powder. I wish I knew as much about my job as I do about movie trivia.


+1 on a dust mask... and I'll raise you some decent gloves. Good winter project.

tin man.

[RBX QB]

tin man.

I can't be held to accuracy (or proper recall) on a Monday.

This thread gets me to questioning anodizing vs powdercoat vs paint. Polished metal has NO place on my bike (I don't want to be seen  ). I'll leave it at that, because I know the merits and detriments of each can be found by searching the forum.

I do like the look of a moderately polished (satin, as the OP stated) swingarm, vs a full (too chrome) one. There have been a few images posted on the site.