Originally Posted by bulgie

I and a few other DIY-ers have made 100 mm BCD rings by taking a 74 mm ring, drilling and counterboring 5 new holes, then cutting the old holes off. Since it's a fair bit of work, I start with the best quality and nicest-finish rings I can find. In my case that was Mavic MTB rings from the '90s, sadly no longer available. TA rings in 74 mm are probably more available and have a nice finish. Tons of other boutique brands made 74 mm rings out of the good alloy, 7075 T6, but some of them (FSA and Vuelta for example) have goofy shapes and/or ugly anodizing that won't look right on a vintage bike. The one 29t I made used a no-longer-available Willow brand 74 mm ring. It had a weird pale gold (champagne?) anodizing that I removed and polished. Looked nice when done, but too much work.

Here's my Flickr on how to make a 100 mm ring from a 74 mm. I didn't even have a drillpress at the time, so this was all done with a hand drill and other hand tools.

Here's a 30t made by Dennis Stover, a machinist who only makes stuff for himself, not for sale, just further indication of what you can do with access to a milling machine.


Dennis used a Sugino ring as his "organ donor".

Mark B

Originally Posted by bulgie

The 30t ring pictured by @merziac earlier is the brainchild of Bob Freeman. He used to have a bike shop (since closed), called Elliott Bay, in Seattle, partnered with Bill Davidson the framebuilder. Bob is retired now but he still does little projects for fun and sells a bit. These rings were made for him by a friend of his with a small CNC milling machine. Last I heard, he couldn't get more rings made because that friend passed away. Because so few were made and they were all sold, your chances of finding one are very small.

There have been a couple other small custom-chainring manufacturers that offered 100 mm BCD rings in the past, sorry I don't remember their names, but I'm pretty sure they're no longer offered. I don't know of any currently for sale, but I'd be glad to be proven wrong — if any BF people know a place, do tell.

The 31t was made by Jim Merz in the late '70s or early '80s in decent numbers, were offered in the mail-order catalogs at the time, but are very rare now. He made a 32t also. which is about equally hard to find.

I and a few other DIY-ers have made 100 mm BCD rings by taking a 74 mm ring, drilling and counterboring 5 new holes, then cutting the old holes off. Since it's a fair bit of work, I start with the best quality and nicest-finish rings I can find. In my case that was Mavic MTB rings from the '90s, sadly no longer available. TA rings in 74 mm are probably more available and have a nice finish. Tons of other boutique brands made 74 mm rings out of the good alloy, 7075 T6, but some of them (FSA and Vuelta for example) have goofy shapes and/or ugly anodizing that won't look right on a vintage bike. The one 29t I made used a no-longer-available Willow brand 74 mm ring. It had a weird pale gold (champagne?) anodizing that I removed and polished. Looked nice when done, but too much work.

Here's my Flickr on how to make a 100 mm ring from a 74 mm. I didn't even have a drillpress at the time, so this was all done with a hand drill and other hand tools.

Here's a 30t made by Dennis Stover, a machinist who only makes stuff for himself, not for sale, just further indication of what you can do with access to a milling machine.
Before trimming the 74 mm holes off:


After trimming to final shape on the mill:


Dennis used a Sugino ring as his "organ donor".

Mark B