Reynolds 

I'm about to make my own chainrings from sheet aluminum using a program that draws sprocket templates. But I'm not sure about the kind of aluminum needed. The guy at the shop doesn't know exactly what alloy is he selling me, but he thinks it's 'too soft'. What alloy would be OK?

roadfix

You should be an expert in aluminum.





Reynolds

Bill Kapaun

I think there's a bit more to it, like "Temper".
7000 series is considered "aircraft grade"

HillRider

There are a bunch of series of Aluminum alloys with different composition, properties and heat-treatment requirements. You probably need one of the "7000" series but there are a variety of grades within this series. You also need to have the proper heat treating furnace and knowledge of how to use it. The technology is pretty sophisticated.

You can make chainrings from any Al sheet you come across but their performance and durability will very likely be poor.

Camilo

I just have to ask why?

TimJ

Well, chainrings are often made of 7075-T6, so... there you go.

cman

because there is some cool designs that lack in todays line up.
https://www.blackbirdsf.org/chainwheels/

BCRider

I've got some Raceface rings marked 6061-T6.

Camilo

cool. I'd be interest in hearing how it goes when you put it to use.

cny-bikeman

Well the particular design you show would possibly be very flexy in aluminum. You definitely would not get away with that as a single - you get some bracing effect when two chainwheels are bolted to the spider.

HillRider

Unless the illustration is lacking in enough detail, I don't see a bolt circle for any reasonable spider size. The only bolt holes seem to be right adjacent to the center hole.

I expect the ring in the illustration was originally made of thick steel in a relatively low tooth count (say 42 or 44) and used for a single speed cruiser application with an Ashtabula-type crank. I can't see it being stiff enough if made in Al of any grade.

operator

Make it out of carbon

phidauex

I would recommend 6061. It is more "machinable" than the 7000 series aluminum alloys. It is slightly less strong, but not enough to be a problem. Many chainrings are made out of 6061.

The -T6 part indicates the level of temper. 6 is the highest, making the most rigid and strong alloy. If it gets hot, and then slowly cools, its temper will drop. At T1, it will be very soft. Since you probably will not be able to heat treat the aluminum to retemper it after machining, your goal will be to keep the aluminum as cool as possible during machining by using cooling water, slow speeds, and machining intermittently to keep it cool.

I recommend onlinemetals.com for metal in small quantities, they usually have a lot of alloys available, and in a wide range of thicknesses.

peace,
Sam

BCRider

Assuming he's doing this with a CNC machine it would have full time flood coolant so heat isn't an issue. If he's doing this on a manual machine with a dividing head then he should be making clocks and not bicycle parts....

biker128pedal

If you machine the flat sides be sure to machine both sides evenly. If you make a nice design on one side and not the other it can warp with age.

BCRider

If it helps you may want to know that the fancier grades of alloy will be stamped with the alloy familiy and the heat treat number. The times I've bought 6061-T whatever there's bands of repeating info stating company name and alloy in one inch lettering and each band is spaced about 10 inches apart. If you buy a 2 foot square piece or larger it's impossible to not know the alloy provided it's something worthy and pricey enough to be marked. Only the softer and unsuitable grades for applications like this are not marked with the alloy and treatment info. All the "aircraft" grade sheets will be marked.

Joshua A.C. New

I'm very interested to see where this goes. If you can produce these in any numbers and for an amount that I can afford, I'm very *very* interested.

Flanderflop

I still want to know how you are going to mount that to the crank.

StephenH

Heck, I was imagining a guy with a vise and a round file, not a CNC setup. But that would surely work better.

I'd go with Phideaux's advice up there.

You may find you have to buy quite a bit more material than what you need. If you're CNC'ing it, can you make two or three spares while you're at it?

Somebody mentioned one of those sprockets being for Astabula crank's- but there's no offset hole on it- you know the hole where the peg goes that keeps it from spinning.

jimmythefly

1. I'm not sure he's talking about making this exact ring, just omething along these lines stylistically.
2. If he were making this specific ring, I'd expect he has something like a set of Stronglight 49d or TA cyclotouriste cranks. Those with mounting questions, google those.

anti.team

There are really only two choices: 7075-T6 or 6061-T6. Those are the only appropriate alloys that you will have any success getting. I would recommend calling a local metal supplier and see if they will sell you drops or remnants cheap.

How are going to machine them?

cyqlist

That would be me. I made the 21 tooth granny ring for my TA crankset sometime back in the early 1980's. I used a 21 tooth steel freewheel cog as a template, bolted to the aluminum, and roughed it out by drilling holes between the teeth and using a hacksaw before going to the round file (and others). I have no idea what the alloy was but it lasted many years and tens of thousands of miles.

HillRider

Interesting project. I assume it lasted so long because it wasn't used much. The bike may have been ridden "tens of thousands of miles" but how many miles were really on the granny ring?

One other thought; instead of using the 21T cog as a template, could you have used the cog itself by drilling it for the mounting bolts? Cogs are made of decent steel but aren't hardened that much and should be reasonably easy to machine.

ultraman6970

One of my friend's made one like in 1984 of solid AL, took the mold from a campy one and then basically he cast it and polished it using industrial machinery, the result was super cool anyways. I believe he still has it so i dont see why u soulndt been able to make one.

Just post your results Good luck

Reynolds 

That will be the second part. First I'll drill the teeth 'holes' with a drill press.
As for 'why', I like to have something unique made by myself (if it turns out good enough to be shown )
Thanks for your responses!