On Tue, 8 Jun 2021 11:59:07 -0400, Frank Krygowski
wrote:

On 6/8/2021 8:58 AM, AMuzi wrote:
On 6/7/2021 10:06 PM, Frank Krygowski wrote:

A bit more seriously: I've sometimes thought it would be
nice to have access to a CNC mill, to refurbish freewheel
cogs. It would keep my ancient SunTour freewheels going.


Is that even possible?* Any material removal just reduces the root
diameter, right?

I don't think so. AFAICT there's no wear at the root diameter. My idea
would be to replicate the profile of a brand new driven surface (the
back side of the tooth) but rotated a couple degrees clockwise. The
result should be a tooth shaped like the original, but not as wide
circumferentially - if that makes sense.

I don't think it will work. By narrowing the tooth and retaining the
original profile, you widen the slot width making it flat instead of
rounded to fit the chain rollers. If you cutting radially into the
slot between teeth, you'll weaken the gear. As long as the chain is
taught, your idea will work. However, when chain tension is released,
there's nothing keep the roller centered between two adjacent teeth.
My guess(tm) is the chain will slide forwards and backwards, miss gear
changes, or do something undesirable.

BTW, I'm not claiming this makes practical sense. My SunTour freewheel
board has dozens of cogs (but not some favorites), and other freewheels
are still available.

Yep. We've successfully transitioned from a very practical "safety"
bicycle, through various levels of absurdity, and are now working on
the ridiculous. Welcome to my world.

--
Jeff Liebermann
PO Box 272 http://www.LearnByDestroying.com
Ben Lomond CA 95005-0272
Skype: JeffLiebermann AE6KS 831-336-2558