Dannyboy21

Edit - I have a 42t that I picked up for a great price in case my experiment below goes pear shaped.

I picked up the 36 t 6 pin eBay ring for kicks. If the bcd is the same, then theoretically 3 of the holes should be in the right spots (at 120° angles) and the other 3 holes will just not be used.

If the experiment is successful then booyah; I have contributed to furthering our knowledge. If not, I will have a 6 pin TA 36t ring for sale. I will post regardless, upon arrival and testing of said ring, of my triumphant experiment or my embarrassing failure.

daka

"Steel ring teeth make sense; the smaller the ring the more sense they make. I suppose the best arrangement would be a U-channel ring of steel teeth with an inner aluminium ring and arms centrifugally cast into the ring and then machined and peened."

That is the intuitive response, but it may not actually be true. Long ago and far away, back when I used to work for a living as an engineer we avoided putting two hard or two soft materials together in situations where they would slide against each other without lubrication (lubrication being a big no-no in ultra-high vacuum field that I was working in). Much better if one piece was hard and the other soft. This could be as subtle as heat treating one for hardness and annealing the other but identical materials together would bind, gall and generally just tear each other up. You can see this for yourself if you take a stainless steel (not plated) nut and bolt, clean them carefully so there is no foreign material separating the threads then bolt them up tight. They will give you a hell of a time when you want to undo them. If you look at common items - engine crankshafts are super-hard, their bearing inserts are always soft metals. Bushings are bronze or even plastic, while the shafts that turn within them are steel. I'm not making this stuff up.

Things are slightly different in the bicycle drivetrain - a properly maintained cycle will have some lubrication on the chain/sprockets so the the base materials seldom actually contact each other and the correct term for bike chains is actually "roller chain" since the part that contacts the teeth is free to rotate allowing it roll down the tooth face rather than slide. But, in the case that the lubricating film is not adequate and/or the roller has too much friction to roll, the two metal parts will indeed slide against each other and now it is best if one of them is softer than the other. When you hear parts "squeak" that is them chattering unevenly as they attempt to slide one over the other.

I personally wish, from a wear standpoint, that the chain was the only sacrificial item since it is easier and less expensive to replace than worn chainrings, but my personal experience is that an aluminum chainring will have a life far longer than the chain that runs over it providing that the things are kept clean and the chain is discarded before it has stretched excessively.

conspiratemus1

^ Thank you so much for that.
Some years back I quoted the (now-late) Mike Barry of Mariposa Custom Cycles as saying that the introduction of "aluminium"-alloy chainrings during his racing career in the U.K. was a great advance because they lasted so much longer than steel. The pseudo-expertise of old-time bike gurus was sneered at by some of the Commentariat here. What did I know? -- I was only quoting an expert. But you would think if steel rings really did last longer, somebody would be making them at the high end and selling them at a premium -- harder to machine and all. Remember that steel parts aren't necessarily heavier than aluminum parts, since the strength-to-weight ratio is close to the same. The aluminum part has to be bigger, witness steel water-bottle cages and racks with their graceful thin lines, as long as stiffness isn't so crucial. Sometimes you want the part to be bigger without being heavier, and then of course the lighter metal wins.

And sometimes it's just better for the application, as you say.

oneclick 

It's not intuitive, it's economic. If one part is going to wear at the expense of another, let it be the cheap one. Chainrings cost more than chains.

conspiratemus1

To test-fit your experiment it is helpful to have the extractor at hand since getting the right spindle to fit the crank is an experiment in itself. You may find yourself needing to torque it on moderately to check for fit, then removing it to try another spindle. Once satisfied, you may not then need to remove the crank again, for years if you put a cartridge BB in. So if you don’t want to spring for a new Stein extractor, and if your mechanic won’t lend you his, I can lend you one of mine for few weeks while you get it sorted out, then you can mail it back to me. P.M. if interested. No charge.

Dannyboy21

Thanks for the generous offer. My mechanic will want to do this. He will welcome the challenge. He is a retired fella who really enjoys when I visit with the C&V bikes. So I will be okay in that regard. Much appreciated, though.

conspiratemus1

^ Even better!

eeuuugh

The rate of wear in a drivetrain depends not only on hardness of parts but the distribution of force. Chainrings wear much slower than cassettes because the pedaling force is distributed across many more gear teeth. A worn chain wears out a chainring more quickly because it rides up the teeth, which are tapered, so then drive the chain with a smaller contact area.
Such a thing exists! Surly stainless steel chainrings. Steels being what they are, this is still a soft metal to hard metal interface--only now the chain is the soft metal.

I believe some 1x12 systems use a hardened steel chain. Not sure what the rationale is.

oneclick 

The damage is not from the roller riding up to a place where there is less contact area, but the pitch changing so that the load is borne by fewer and fewer teeth; in the end it is only the single tooth that catches the chain. You can sometimes see this in the changes to the tooth profile on aluminium chainrings - the surface will creep sideways forming a ridge. It's not actual wear, the metal is still there, it's just so soft that it's been pushed sideways.

conspiratemus1

Just between you and me, we currently have a steel granny ring on the tandem. Hedging our bets, I guess.

daka

The Surly website describes the stainless steel chainring as being made from AISI 304 stainless steel. The austenitic stainless steels which include the 300 series are not heat-treatable and cannot be hardened. Although we do not know the alloy or post-treatment used for the chain rollers, it is likely that they are still harder (and stronger) than the chainring.

oneclick 

304 is not a hard - or hardenable (by heat treatment) steel. It's the same stuff in your cutlery drawer. The rollers are undoubtedly high carbon steel, heat-treated, and harder.

Dannyboy21

So the 36t ring fits on the crank. Not an ideal fit and I had to put the crank bolts on backward (for now) as the small ring holes were not big enough for the female "nut". I may drill them out if after test riding the 36t ring is not too flexy and the shifts are good. More to follow.

Dannyboy21

Resurrecting my own thread. I got ahold of some NOS and mint Suntour Superbe Pro bits and decided to build up this 78 Competition GS frameset. I put the TA crankset on it with the 36T, 6 hole "Mickey moused" on to the 3 bolt crank. I had to reverse the female and male bolts to make it work as the bolt holes on the 36 tooth are smaller. But aftern3 rides I can say the crankset has worked very well and the Suntour stuff, well, let's just say nobody has to do any convincing with me about the merits of Superbe.

kroozer 

Beautiful bike! I'm glad the chainring worked out. 36t is a nice ring size, low enough to give you a good climbing gear, high enough to still be useable on roads.