Is that a 110 BCD small ring? That only gets you what, four teeth smaller than the smallest 122 ring?
I'm holding out for a 26-tooth granny.
In any case, I'm pumped that other people are getting involved in this. I've wanted one of these things for a long time!

Maybe, but measuring that diameter with a regular old metric ruler I get about 106 mm. This is a Stronglight 93 ring we're talking about? I don't see any dimension that looks like 117 mm.

Here's a pic of the hypothtical triplizer I've been trying to get someone to make for the past 6 months.

Uuuh. I pulled a NOS 40t ring for a 93 from my box 'o parts and laid a ruler across it. This was not from bolt holes, but from the inner rim. Not a precise measurement, but it sure looks like 117mm to me.

Am I missing something here?

I don't know if these will display right. If not, I'll be editing the entry.

Between digging in the archives, and help from the CR list, the maker has been found in Japan. BUT, it is still unclear if he's still making rings or not. The main page displays code rather than Japanese (as if that'd help!), but the images are amazing. SO, I understand, are the prices. Think $175 or so per ring. But these are custom made per order, so, according to the deep pocketed collectors, reasonable. Sigh. Anyway...

Check out these tasty photos:

1957 49x36 - perhaps chrome plated steel?
[/url]
... [ Stronglight made similar looking 5-pin steel chainrings https://www.velo-pages.com/main.php?g2_itemId=11532 ]

1957 type 49d 5-pin 48x36


105-bis 36t


mod 63/93 50x37


Here's a mod 105/93/63 adapteur. In this case for 42x32 inner rings


More, as we discover more.

My eyes are not that great, but that measurement appears to me to be 107 mm, not 117. Maybe there's something I don't understand about what's happening at the other end of the ruler?

Ah, wasn't sure what a "triplizer" was! Pretty obvious now that I see it. The granny needs spacers, yes? What's the inner bcd we're after here?I'm thinking outer and granny rings to match of course. Something like 52/38/28? Do you have this drawing in a cad format (something other than a *.jpg). I can copy/paste/scale/vectorize in my software so not a deal breaker if you don't. I'm off to the shop to grab my crank after I get some coffee in me. Then I can get back to work on it.

PS looks like 107 to me too.

Well. Duuuh! was right.

107mm.

My plan was to go for 42 triplizer ring, so traditionalists could go with 52/42/30, half-step true believers (like me) could go with something like 46/42/24 with a five-speed 14-17-21-26-32. (I want a gear low enough to climb Mt. Ascutney--long stretches of 19 percent grade.) I think a 47-42 also works well as straight crossover gearing with a 13-15-17-19-21-24-28 in back. I may have gotten the 47 and 46 switched--I charted both of those out once, but don't have the numbers in front of me now.

Cad work is done! This has a 122 bcd with a 74 bdc for the inner. Got that from Sheldon as the "standard" inner for a triple. Would allow for a 24t granny, again from Sheldon. Inside diameter is 60cm as per jonwvara's drawing. Any input before I move on to the CAM side of the work?

Wow! You're all over this. Yes, you're right about the ring bcds and tooth counts. The 60 mm inside diameter is kind of arbitrary--it just looked good to me. The important dimension is the 107 mm larger inside diameter where the cranks spider fits against the ring, just inside the 122 mm bcd bolt holes.
Assuming that it really IS 107 mm, that is. That measurement is just based on a rough-and-ready measurement with a ruler--not sure it's precisely right. I would be more than happy to let you borrow a standard Stronglight 93 ring so you won't have to guess on any of the dimensions. Send me a PM with your address and I'll drop it in the mail.
JV

I'm trying to decide which siren call to heed: a 36t inner ring on a double, or a triplizer.

For me, the 42 middle is almost a deal-breaker, because I'm already finding my 38 inner ring so useful.

I think a compact range with the mid ring at 40 makes more sense. 48-50 for top end. But that's just me.

Amazing progress, eh?

I could live with 42 in the middle and that'd leave my 52 for the occasional overdrive gear or two and I'd have enough on the low end just using a 28 tooth inner ring. It turns out on both the stronglights I have the 52 rings are basically toast anyway so I'd happily run a 42-28 compact double and eventually snag another 52 ring off ebay or something... 'course there will be derailleur issues to sort out too. Anyway this is an exciting thread now!

Amazing progress, eh?[/QUOTE]

You've got that right. Things were barely smoldering before. Thanks for blowing on the coals and getting an actual fire going.

I was going to say that I didn't think you could run the granny gear of a triple as half of a compact double, but I guess you can if you use some kind of a "bash guard" instead of an outer chainring. Not sure how you'd find one in 122 BCD. Maybe you could grind/machine the teeth off a 52-tooth chainring? They seem to be abundant and pretty cheap.

You want the bash guard?

https://www.ebay.com/itm/STRONGLIGHT-...item3a6b292694

This is its second time around. It has one bid this time. It's light, but puts a big "face" on the crank. I tried one once, but then took it right off. Doing the compact double, tho, might make it worthy.

Here's what it looks like mounted:

Shouldn't need it. I got the measurment off my SL 104 ring, came out to 107.5 or so. I got the CAM side of things last night. Now I just have to get some material and some free time in the machine! There's a fair amount of real-state in the triangle area over the inner bolt circle. Should we skelatize this. Or we could do some "drillium" work on the whole thing. Or custom "panto" work.... Thoughts?

Nice bashguard, I'll try and keep an eye on it.

I was planning to just leave the 52 on as a vestigal ring but I had also ready to leave the outer ring off as gauche as that may be. I've given even less thought to the derailleur situation but I'm currently trying to resurrect the triplex sport that was shifting the crank.

edit: or run this triplizer on the outer part of the ring?

I think the crank spider would be in the way.

118mm is SR Apex, not Zeus. Zeus was 119mm and unique. Why is it so hard to find a really complete BCD reference chart? I've never found one.

I'm a pretty utilitarian guy, so my opinion is that "skeletalization" of the ring or any other elaborate treatments are likely to be more trouble than they're worth, given that this is a middle ring--it's not like it's a main design feature. Also, I think we want it to be pretty robust, since the load on the granny gets transmitted through it. Trying to lighten it too much might reduce its stiffness enough to cause problems.
I say build a simple one, see if it works, then get fancy later if it seems worth it.
Of course, you can also design something by making a prototype that's as light as it can possibly be, run it until it breaks, make a new one that's stronger in the broken area, and repeat as many times as necessary until it no longer breaks. That works, too, but it costs more and takes longer.
JV

Sounds good. first part(s) will be made like the above drawings. As far as 'more trouble then it's worth", almost no trouble at all! the materials aleady in the machine and it doesn't care if i wanted to drill one hole or turn the whole thing into chips. I'll be making this out of 7075 T6 aluminum which is far tougher stuff than the alloys of days past. Should hold up all kinds of abuse and last a long time...

Or do FEM to determine strenght requirements.

Who else wants one of these? I'll be making a few. Once set up, CNC's really show their worth when making quantities. Other designs (hopefully) to follow, feel free to PM or post with inquiries. This is pretty cool, "I love it when a plan comes together!"
-Andy