Polishing clear-coated aluminium parts

[rmwesley]

I feel as though I'm underachieving getting old clear-coated aluminium parts looking fancy, e.g. crank arms, brake arms etc.

My usual approach is wash with warm, soapy water then a *lot* of elbow grease and Autosol, rather than attacking anything with the polishing mop and compound.

However, it leaves the parts a bit lacklustre.

I've seen a few people stripping the clear-coat completely, then polishing the bare aluminium, but don't want to go that far.

Does anyone do anything different to get a better finish on the clear-coat?

Cheers, Richard

 

[Mod-Master]

If the metal underneath is polished then just keep wet’n’dry sanding up to 3000 grit or something like that.

That will probably achieve the best as autosol only works on metal.

Or use t-cut or g3

 

[foz]

Autosol will not give a brilliant shine on anodised or clear coated parts. If you want a mirror finish, they need stripping back to the bare metal. An a polishing wheel will give better results in less time than hand polishing

 

[Tootyred]

Sadly above is true. If the clearcoat is unbroken, leave it well alone.....however, in most cases, especially on cranks with rub or even damage that's not going to be the case.

You need to completly remove the clearcoat to be able to get at the metal below to polish it. This can be done a couple of ways.....either chemical or wet and dry.

Chemical is a bit fraught with issues as some alluminium will dissolve in the sheep dip.....we found this out 40 years ago when we ate a customers suzuki fork top tree! Plus the chemicals are not realy home use friendly!

So your into wet and dry, then polishing through the grades. If its got major damage or your reasonably skilled, you could try dronco discs. But be careful as the cut pretty fast and you have to understand that reshaping damage is a global approach, as isolated patches will show up in the light on the final polish.

I went through the process on page 4 of this thread....lots of polishing on this one! Might help as it has some basic kit details too.

https://www.retrobike.co.uk/threads/85-saracen-conquest-what-have-i-started-finished.445308/page-4
But don't blame me if you get addicted to polishing.....i find it very cathartic!

 

[Mod-Master]

polishing is addicting… as soon as I used autosol on a rear mech then I achieved a mirror finish. I can literally see my face in it.

The Shimano cranks like your don’t come polished do they?

 

[Tootyred]

Not many shimano parts were polished. Some very old bits were, but nearly eveything from the mid 80s on (only going on experience....don't actually have a date), have been clearcoated......or clear anodised.....im not sure what it actually is......

The coating gets thicker as time goes on. Early 700 series stuff has a very thin layer that will easily rub off. By the time you get to 92 xtr etc, its pretty thick and harder to remove. Probably partly a result of better clear and processes.

If you want matt finish, just dont go right through the grades.

As for re-clearcoating.....my advice would be don't try it at home. Alluminium surfaces corrode almost instantly ( its why they are an arse to weld well) and getting good adhesion is not easy. With paint you can etch, but clear......

 

[Tootyred]

To give you an idea, an older xt rear mech or chainset from the m730 series, will polish with a sisal mop, straight through the clear as though its not there.

On a latter m737 chainset or xtr, you need some pretty serious wet and dry (or grinder with dronco if you have the room to work) to get the layer down first. I avoid small parts like that having painfully refinshed a m900 front and rear mech.

 

[Mod-Master]

If you don’t want to remove the clear coat then t-cut or g3 is best. But if you want a mirror shine or something close then you’ll have to take off the clear coat to get it, as you can’t polish the metal under the clearcoat

 

[rmwesley]

Many thanks for all the replies.... always good to know what other do. I'll break out the polisher Normally just use it for steel, so will get another set of mops / compounds for non-ferrous parts.

 

[Suprachrgd82]

Polishing aluminum parts just irks me. I love watching the youtube resto videos, but I cringe when I see hosts polishing cranks.

Aluminum parts are anodized, which is a hard protective layer that resists scratches and corrosion. Clear coated parts have an additional layer of corrosion protection. To polish parts, one must remove 1 or more layers of protection, leaving the raw soft aluminum to oxidize almost immediately. Every drop of water, fingerprint, cleaning agent, ambient humidity, etc is making that polish haze over and pit.

As far as I am concerned, parts polished at home are worthless.