[CR]32 T/ 100mm BCD rings for Campy R/NR triple cranks - make your own


Example: Framebuilders:Norman Taylor

Date: Tue, 24 Feb 2004 16:26:08 -0500
To: classicrendezvous@bikelist.org
From: Larry Osborn <losborn2@wvu.edu>
Subject: [CR]32 T/ 100mm BCD rings for Campy R/NR triple cranks - make your own

Greetings campers and CNC-phobes

Can't seem to avoid getting involved in any of the discussions about triple cranks, triplizer rings, etc. Just thought it was time to share the latest chapter in my ongoing conflicts with those things. The fun never stops.

This all sort of came out of my long running displeasure with the Campy R/NR triple cranks with those miserable and scarce 36 tooth "small" rings on a 100mm bolt circle diameter. Sorry, 36 T is a middle ring for me. But sort of stuck with that arrangement on a couple bikes that I want to keep close to component correct ( I should know better by now), but that I still want to be able to ride, in some hills that I'm also stuck with (I should really know better by now). I wrote some pretty nasty things about Tullio and the gang right here, but decided to edit them out.

Yes, I've heard the fables from the misty past, where legendary men with machine tools created special rings. 32 teeth. Maybe even 31 teeth! And I've heard the rumors that some glorious day those legendary men might hear our weeping and wailing and gnashing of teeth, return to their idle, darkened machine shops, and recreate those mythical chainrings of yore for the oppressed and kneedy. But ya know, it just ain't gonna happen. And I have yet to see one of those mythical 32 or 31 tooth Merz, Mikelson, Avocet, whoever rings materialize anywhere. Not at the swaps, or ebay, or anywhere. And besides, where's the fun/challenge/adventure in just sending a whoppin check off to Highpath for a custom ring? I just can't do it. Too boring.

SOOOOoooooooo, not one to take "No" for an answer from the real world, or from fairy tales, it was time to take steps. 32/31 teeth is the lower limit with a 100mm BCD. Looking at what might be available in the real world that could possibly be modified; 110mm 32 tooth rings, even if they exist, weren't going to leave enough metal to work with, and 74mm 32 tooth rings, even if they exist, were going to need a lot of metal removed and maybe look a bit silly. Or at least obvious. I still haven't consciously accepted the existence of 94/58mm mountain bike bolt patterns as anything more than something I reflexively throw back into the bins while scrounging for "usable" chainrings (always at least 2 decades and 2 bolt patterns behind), so it took a while to reach the point where I even considered that possibility. But when I got there, the door sort of swung open. Hey, 94mm is darn close to 100, and the metal that needed to be removed to reach 100mm is in the beefy part of the ring. It's not going to become fragile. They are readily available with 32 teeth, new and abused, cheap. Just need to extend each bolt hole by 3mm (by some reliable, manageable means yet to be determined) so it becomes more of a slot, round at each end..... yeaaaaaah, this could work. I love this plan!

The first trick was finding flat rings. Rings that weren't cluttered with shift ramps and pins, and none of that pesky and obviously UN-vintage purple anodizing. I skipped merrily up to the Westminster swap hoping to find a used ring to experiment on. Instead I found two new ones. Kinda pricey for an experiment, but they were going to be sacrificed for a greater good...... and I was holding them right there in my trembling, frostbit little hands, the item at the very top of my swapping list, not 2 minutes after walking in the door. That NEVER happens. Might never happen again. I took it as a sign and just coughed up the $$. Another offering in the name of St. Frederick, the patron saint of Flintstone mechanics, machinists, and woodworkers.

Weeks later, back in the labORatory.... Finally had a few days without additional snow, I had my trench dug out to the garage, so it was time to do the deed. Not going to corrupt your creative thinking by telling you how you should do it, or embarrass myself by telling you how I did it. I tried a variety of approaches, using what I had, but didn't have what I wanted. I eventually lost patience trying to finesse it and went totally Flintstones on it. Let's just say it wasn't a pretty thing to watch this time around, but I can do better. Also didn't take the time to carve out the recesses for the bolt heads, so at least for now the bolts aren't flush with the face of the ring. Boo hoo. Maybe next time. And nobody says they have to be recessed anyway. So there. A milling machine would have been nice, but even with simple implements of destruction like a Dremel, an air grinder, some sort of metal munching bit in a drill press used like a router/shaper table, or even just a nice slow safe 3/8-inch diameter rat-tail file (which is just slightly smaller than the 10mm diameter of the bolt holes), and some patience, you CAN try this at home. And you have 5 holes to practice on to get it right. My only advice is to take little bites. Don't be afraid. It's just aluminum. You're not going to have to call in the Haz-Mat team if you make a mistake. Paramedics maybe, but that depends on your personal relationship with tools. (Just a little safety tip from your Ol' Uncle Lar. Never try silly stuff like this until AFTER the snow plows have come through.).

Most of the imperfections conveniently disappear under the bolt heads or behind the spider arms, unless you totally lose control of your chosen tool and make a rather dramatic transition into free-form abstract engraving. Turns out very functional. Not precise enough that I would put my name on it to impress anybody, but this is a user ring. Close enough is good enough. AND the ring will be micrograms lighter! Yeah, a little like making a sow's ear out of a silk purse, but that's okay. I'm not proud. And once the whole fiasco is safely hidden away on the bike, the only really noticeable evidence that something is not quite Campy is that the Vuelta ring I used isn't nearly as highly polished as the Campy rings. I repeat, Boo hoo. It's the inside ring. And anybody who tries to examine your work up close and personal is going to bonk his head on some other adjacent component or frame tube long before getting close enough to aim his bifocals. Serves 'em right. I like seeing chainring grease-prints on a person's leg, but I tend to stay a safe distance away from anybody with a similar imprint on their forehead.

Maybe those 4 fewer teeth won't make a difference for you. They will for me. Not enough of a difference, but better than doing nothing and taking it in the knees from Tullio. The knee quacks have been on my wheel a long, long time, and I'll use any edge I can to maintain even the smallest of leads over that pack. That occaisional glint of surgical steel behind me provides more than ample motivation to try silly projects like this. And if you don't need that, think of it as just thumbing your nose at the gang at Campy for creating this thing in the first place. Always works for me.

"The reasonable man adapts himself to the world. The unreasonable man persists in trying to adapt the world to himself" George Bernard Shaw

But wait, there's more! I have another of those miserable cranks. And since the first operation was relatively successful, and I still have another ring to play with, and swap meets coming up where I can find more...... I could get good at this. If I wanted to. If I had to. MMMMMmmm, 74 mm BCDs. Tune in again next time for another thrilling episode: "Fear and loathing in the workshop", or "The toothless get ruthless".

Larry "Reasonable AND unreasonable" Osborn Doin' the Subaru slide, downhill sideways in no-wheel-drive, sliding in the general direction of Morgantown WV