Re: [CR] Campagnolo Crank Crack -- Should I be worried?

(Example: Events:Cirque du Cyclisme)

To: <classicrendezvous@bikelist.org>
Date: Mon, 19 Jan 2009 20:31:48 -0800
From: donald gillies <gillies@ece.ubc.ca>
Subject: Re: [CR] Campagnolo Crank Crack -- Should I be worried?


Incidentally, you are trying to file out the crack so that not only is the crack completely removed, but ALL defects in the file-out area are completely removed !! Don't just stop when the crack is gone, because the file will leave scratches which are stress risers!

Buff the area with 1000, 2000-grit sandpaper, and use nevr-dull or simichrome or a flap-wheel/dremel to finish the job beautifully. After that, I'd get a red magic marker and mark & wipe the area a few times as a poor-man's dye penetrant test.

Precision polishing will raise the fatigue limit of the piece. In the M.S. thesis below, polishing raised the fatigue limit of some aluminum samples by about 50% (figure 18):

http://fcp.mechse.uiuc.edu/reports/FCP_Report153.pdf

When you can no longer see any crack and when the area shines like a mirror, you are done!

- Don Gillies
San Diego, CA, USA