At 8:22 AM -0800 1/22/08, Tom Dalton wrote:
>CNC!!!! Eeek!!!! Okay, maybe I'm just clueless, but when I think
>of CNC, I think of all that dreadful 1990's small batch
>manufacturing that gave us Kooka cranks, Paul's derailleurs and the
>like. It started in the MTB market and infected the road market.
> they also just kinda sucked. I think Shimano put it best in one of
>their ads that read something like: "Yes, we make CNC machined parts
>from aluminum alloy billet. We call them prototypes." I think
>declinig costs of CNC equipment was the pathway that allowed a lot
>of self-annointed parts engineers to make expensive junk on a small
>scale. Quaility bike parts are better made using hot pressing, or
>forging techniques that bring the part close to final shape prior to
>machining.
Different manufacturing techniques are applicable to different components. The problem of many small shops is that they master one technique and apply it to all their products.
CNC machining may be fine for hub shells and headsets, but it is less suitable for cranks and brakes. Today's small makers get around that by beefing up their parts. A CNC-machined Paul Racer brake weighs 50% more than the forged Mafac model...
Forging also allows you to use less material, which is why big makers forge hub shells, and then machine them, rather machine them from a big rod. Especially for high-flange hubs, this can make a big difference in your materials bills - once you have recovered the $ 6000-10,000 for the tooling.
Maxi-Car hubs are a case in point: The Type 1 shells ("stepped shape") were machined as small-flange shells, to which the large flanges were riveted. Obviously, in the 1940s, aluminum alloys were expensive, and labor was cheap. Type 2 and Type 3 shells were machined in one piece, resulting in a huge pile of aluminum chips. I assume that labor had become more expensive, and aluminum cheaper. Type 4 shells ("hourglass" shape) were made from forged blanks, which then were machined to final shape. Perhaps they were selling enough during the 1980s to warrant the investment. (I know they had 1000 raw forgings left over when they stopped production, so perhaps this did not pan out as planned. They recycled them before I got there!)
Regarding quality differences, I haven't seen any early hubs breaking, despite having thinner flanges and being machined...
Jan Heine
Editor
Bicycle Quarterly
140 Lakeside Ave #C
Seattle WA 98122
http://www.bikequarterly.com