Re: [CR] Was Velo-Mine polishing - Now crank arm breakage

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Date: Thu, 01 Apr 2010 15:59:38 -0800
From: "verktyg" <verktyg@aol.com>
To: damien roohr <droohr@comcast.net>, Classicrendezvous@bikelist.org
References: <1341534334.6762921270158063557.JavaMail.root@sz0151a.westchester.pa.mail.comcast.net>
In-Reply-To: <1341534334.6762921270158063557.JavaMail.root@sz0151a.westchester.pa.mail.comcast.net>
Subject: Re: [CR] Was Velo-Mine polishing - Now crank arm breakage


The satin anodized finish was always one of the charms of Campagnolo components. Same thing with Cinelli bars and stems.

The thin anodized layer covers soft aluminum which can still be easily scratched or gouged. That's one of the downsides because the damage stands out against the satin finish.

The anodized finish is composed of aluminum oxide with a Knoop hardness of 2100+. This is much harder than most abrasives used to polish aluminum except silicon carbide with a Knoop hardness of ~2500 (diamond is 4-10 times harder).

The harder anodized layer resists the abrasive cutting action of most polishing compounds which can result in much faster removal on any uncoated aluminum surfaces resulting in a shiny but uneven finish.

Without getting into how Velo-mine gets around this problem, I wonder how much base aluminum gets removed with a corresponding loss of detail?

I think it's fine for an owner to customize their parts anyway they want.

But... I too am leery of buying "crow bait", bright shiny objects (that maybe shouldn't be bright and shiny).

On the technical side of things, sometimes polishing is used on highly stressed parts to help prevent cracks and stress risers. When testing material tinsel strength, there can be a significant difference in strength between a polished and non-polished test specimen.

So... It's a long shot, but polishing old Campy cranks could possibly prevent breakage! YMMV ;-)

Remember, paint can hide a multitude of sins!

Chas. Colerich Oakland, CA USA

damien roohr wrote:
> re -
> Buying refurbished parts where one does not know what they looked like before polishing, is
> something I would shy away from for a rider bike, but not polished
> parts as a type.
>
> Very well said -- i completely agree!
> There is an old saying in the world of cars and car parts: "if it don't go chrome it!"
>
> - the natural correlation to bike parts is that "if there are fatigue issues, polish it! "
>
> Beware of shiny used stuff!
>
> damien roohr'
> canton, ct