Re: [CR]CR: Polishing/Buffing Oxidation on Alloy Crank Arms (David Allen)

(Example: Framebuilding:Norris Lockley)

Date: Mon, 24 Jan 2005 21:40:14 -0800
From: "Kurt Sperry" <haxixe@gmail.com>
Subject: Re: [CR]CR: Polishing/Buffing Oxidation on Alloy Crank Arms (David Allen)
Cc: classicrendezvous@bikelist.org
In-Reply-To: <a05210672be1b7442cf92@68.167.248.39>
References: <12c.55e82d3a.2f2712b8@aol.com>


On Mon, 24 Jan 2005 20:05:32 -0800, Jan Heine <heine93@earthlink.net> wrote:
> Polishing aluminum isn't hard, it's just hard work. Don't ask me
> about the hours spent on my Herse tandem that had spent at least 15
> years in an aviary! Especially high-strength alloys (such as 7000
> series) oxidize readily and relatively deeply.
>
> Here is how:
>
> Sandpaper first. Start with 400, if that doesn't yield results, go
> coarser, all the way to 180 grit. Once all the oxidation is gone,
> you'll need to get it smooth again (remove the scratches from the
> sandpaper).
>
> To do so, move in small steps toward finer grits, all the way to
> about 1500 or even 2000 (the finer ones are available in auto parts
> stores for rubbing down paint). Sand in one orientation with one
> grit, then 90 degrees to that with the next finer grit. This allows
> you to see whether you have removed all the previous scratches. (If
> you don't get them all, you have to start over, as there is no way
> you'll remove "320 grit" scratches with 1000 grit sandpaper.)
>
> Once you are done with the sandpaper, it should look close to
> polished, but holding it against the light, you see the scratches.
> Then polish with whatever. 3M makes a product for cleaning aluminum
> boats that removes a lot of material, but you need to follow up with
> a finer compound.
>
> Don't worry about strength, you'll take off not even 1/10 mm of
> material unless it's a lost cause.
>
> If your cranks were anodized, the anodizing will be gone once you are
> done. So I do this only with non-anodized parts.
> --

Good results can be obtained in a fraction of the time using only 400 and 200 sanding steps, straight to a wax based product called "bobbing compound" on a clean muslin buffing wheel, followed by Fabuluster on another clean wheel. A 6" wheel turned at around 1800rpm will work best although it isn't terribly critical. This will work on most Al-alloys seen on vintage bike components- though notably not the alloy used in the bodies of vintage Record FDs.

Kurt Sperry
Bellingham WA