I’m running a 3t 9-32 11-speed cassette on my gravel bike. I love the gearing this gives me with a 40/26 crank. But the largest cog is alloy, and is now skipping badly under pressure so is essentially not useable. I’m surprised because I really don’t use this gear that often. Unfortunately 3t no longer makes this cassette. I believe it was actually made for them by e*thirteen and they do not have a replacement cog available either.
Does anyone know of a source for custom CNC machining of cassette cogs? I expect it is going to be very expensive as a one-off, but really don’t want to change my entire drivetrain.
I’m also not sure this is the best forum for this question so if there might be a better place to ask please let me know!

Machining a replacement cog will be rather involved and costly I also suspect. I know of no one doing such currently with rear cogs. There are a very few outfits that make custom chainrings... but all of these I've seen didn't have any shifting aids, just symmetrical teeth. Does your large rear cog have shift gate currently?

The skipping on that large cog could well be from mere wear, the typical chain wanting to ride up the tooth's face more and more as all wears, until the chain finally reaches the tops of the teeth and thus skip over. But skipping can have other reasons that I would want to eliminate before spending big bucks. twisted teeth, poor low limit screw adjustment, improper "B" gap (worst on that largest cog...) among the common other reasons. The freehub body's ratchet could be skipping, have you visually confirmed that the chain really is skipping over the teeth or just assume that? Has anyone else ridden your bike and offered comment on the problem?

I have to admit that your set up is so far from my happy zone that were I to be dealing with this my solution would be quite different. I have zero need or want for such high a gearing as a 9t will get me. I can go 50+mph down the biggest hills in our area by tucking and coasting. A 9x44T ring is about a 132" gear, no way I can spin that at 90 cadence on the flats. So I would never have a cassette with that high a gear. Andy

Perhaps the answer today is unlikely/impossible. Nevertheless, technology has come so far that OP can even ask the question. This custom technology may well be possible tomorrow in any bike shop, or even closer to home.

40t x 9 is slightly lower than 50x11 and slightly higher than 50x12.

Its high for gravel but depending on conditions it’s not excessive.

Anyway, I’d be checking derailleur hanger alignment, the derailleur, cables, chain, limit screws, tension, and gunk all before worrying about a new cassette.

Are you skipping in both the 40 and 26? It could be a chain line issue too.

All cassettes are eventually wear items. If it’s not today, it may be next year.

I’d be uncomfortable with the “last in the world” cassette. You need to make a plan for when that happens. Possibly eBay, but more likely moving to a different cassette.

How about one of the Miche cassette offerings?

https://www.miche.it/en/products/cas...ds%5D%5B0%5D=2

The 2 Miche cassettes I’ve used were their cheaper ones and were for Campag. The cool thing with them was that they all had separate rings so theoretically you could mix and match. I did with a 12-25 and 13-29 and don’t recall any issues.

The problem I see is that the OP almost certainly has an XD or XDr driver to accommodate the current cassette. Those are one piece. A brave soul with a dremel tool and time might be able to make something happen.

There would be the issue of prying the largest cog off as well. I know it can be done on 11 speed sram. I had a 10-42 cassette that I modded into a 10-44 with a wolf tooth aftermarket cog. I don’t know if that’s possible for the 3t.

If you're dead-set on finding a single compatible 32t you might try AliBaba as a last resort since I have not seen any other offerings. I have never purchased from them nor intend to but they do offer many unusual parts not found anywhere else but no guarantee of quality. There is a chance of cannibalizing cogs from Shimano or SRAM cassettes but it gets complicated trying to find out if the cogs have the same thickness needing special spacers or is part of a riveted together cluster having different ratios and not useable as a single cog, etc., etc. Shimano's site shows exploded diagrams of their cassettes which show which cogs are single or part of a cluster Here is a list of Shimano cog thicknesses by number of speeds to compare to yours. Scroll down to "Sprocket spacing and cassette widths" https://bike.bikegremlin.com/209/bic...ear-sprockets/

Manufacturing a single cassette cog is not particularly challenging -- no more so than a chainring, which are made on small scales, and which I've made in my shop. Any problems would likely arise from not requiring a single cog, but rather a group of them all riveted to a holder, which obviously increases complexity. And, of course, finding someone who can and will manufacture such for a price that the user is willing to pay, and that might be the eventual roadblock.

Any required spacers are almost trivial to make, now. Just draw whatever you need and have it 3D printed. Will cost under a dollar, plus shipping.

You could always make one, using nothing more* than a bench drill, hacksaw and file. And a sheet of dural. The HPV people sometimes make oversize chainrings, they probably have the information you'd need for marking out the teeth.

* obviously it would be easier with a CNC mill, or at least a rotary table for the drill, but you could do the whole thing with nothing but hand tools. This guy does it with a 3D printer and a router:

How long do those last, I wonder?

I guess it mostly depends on the grade of alloy you can readily obtain. 7075-T6 looks like a good choice, but the nearest I can find is a supplier in Poland with high delivery cost. I expect there are more convenient sources but my search didn't find them.

High-Strength 7075 Aluminum Sheet 1/8" Thick, 12" x 12" https://www.mcmaster.com/product/8885K15

$63 per square foot.

How long did 3t offer replacement parts before they left their customers high and dry? They have a legal responsibility for at least a few years.

They do?? Andy

The previous poster appears to be referring to a common misconception regarding US law regarding automakers -- but there is actually no such requirement, even for them, and certainly not for bikemakers.



And furthermore, due to a few ten million people voting last fall to destroy the United States, even if there was such a law, it would be as meaningless as the rest of our laws currently are.

If the item has a warranty, they have to be able to make good on that warranty by either offering the part, a suitable replacement or a refund. Which I believe is US law, but doesn't apply to non-warranty situations.

This isn't a warranty, but it is the kind of thing that I think consumers should take up with manufacturers when they create this sort of bottleneck. 3T got people to buy a certain gearing set up that only works because of their proprietary 9t cog, and then they bail and you now have this very silly chainring pairing.

It obviously depends wildly on the material used, and the method of construction. Simply routing the edges as done in the video has little effect, but I cut my rings with a plasma torch ( 15k degrees Celsius give or take ). That leaves a hardened edge, which is the critical area, and which is beneficial in this application. With the router method from the video, there is a conflict between choosing a hard material and being able to machine it. Your garden variety router may struggle with some harder materials, and/or you will have to feed very slowly.

I have not run any of mine long enough to know the actual lifespan, but after ~2k miles, I can barely measure any wear, so I'm not concerned that they will die young. I cannot measure any wear-rate difference between the aluminum and stainless steel rings that I've produced. That said, I tend to keep my drive trains clean and well-lubricated, and don't experience as much wear as many people do, even with commercially-produced sprockets and chains. So YMMV, literally.

As an aside, I quoted a price for 1/8" 7075-T6 a couple comments ago. FYI, in case anyone is pursuing this, 1/8" is too thick, the quote was just to give an idea on a source. You actually want 12ga ( .0808 ) for at least anything <13 speeds. Not sure about 13s.