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Source for (oddball?) flat sprockets?


Active User
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A couple of years ago I am pretty sure I found some flat chain sprocket blanks without a drilled center hole, just a located center drill point so I could bore out to the shaft size I wanted.

The sprockets I find now all are already center bored for the smallest shaft size the manufacturer thinks is appropriate - in my case I'm looking for a 40-series roller chain sprocket with 15 teeth. They come pre-bored for 1/2" and that's way bigger than I want.

Bushing down is not a great option because my plan is to bore to accommodate threading the center of the sprocket and then securing it to the shaft with a jam nut on each side. Can't really do that if I want a 5/16" shaft and the hole is already 1/2".

Has anyone seen a source for un-bored sprockets or am I imagining that I found them a couple of years ago?

Thanks in advance

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Ulma Doctor

Infinitely Curious
Active Member
Hi Stu,
unfortunately i only see 1/2" bores from my suppliers :(
i suppose you could get a standard 15t #40 sprocket and press fit a slug of cast iron or a steel of choice to a 3/4" or 1" bore #40 sprocket.
bore and face it to length.
you could then indicate, then bore the center to dimension and thread the center accordingly.
it's the next best thing to a fixed bore of the right size.
maybe others may have another suggestion!
all the best :)
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Active Member
Active Member
#40 chain is capable of a lot more torque than a 5/16 shaft can tolerate. What is the application? Maybe there is an other solution that would present less problems. Would machining a hub to fit 5/16 to 1/2 with screws through the flange work?


Active User
H-M Supporter-Premium
Sorry don't know a source for such sprockets. I don't know much about your projected application. No offence intended but sometimes when I couldn't find the parts to make something my way its because there is a better way to go about it. How wide is the chain? Do you do any welding?


Global Moderator
Staff member
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Here's a shaft hub that would probably work. They don't offer one in 5/16" but do have it in metric 8 mm bore but it is out of stock.


Here's the inch selections that they supply,too. Again, no 5/16 bore



Here's another one that will fit the bill perfectly. You not going to like the price on it!!!


I'm sure if you look around and check with a local bearing distributor, you could get it at a much lessor price.
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Active User
H-M Supporter-Premium
Thanks all for the pointers - apparently I was dreaming when I thought I got un-drilled sprockets two years ago. Or maybe they were bored to 1/2" and I cobbled together what I have now which is rather ugly but functional in a hillbilly way.

The application is a cuckoo clock that the hands are driven by a pair of stepper motors through a 300:1 worm-drive and then a 2:1 chain sprocket drive to the hand shafts.

This current incarnation is a 'get-by' proof of concept. I figure I will use cogged belts in the finished design (quieter) but those pulleys are four times the price of simple chain sprockets and I need to get the design parameters tied down and tested before going that route.

I am getting in to 3D printing very soon and the actual cog belt parts will (I hope) be 3D printed after I crawl up the learning curve.



Active Member
Active Member
Make one...

Just get a 1/2 bolt and center drill it with your lathe for the shaft size.

Then drill from side on a flat for a set screw to lock to shaft.

Face of extra material from both head of bolt and nut body of bolt to make a bushing with locking set screw.

If you want to thread to shaft then thread the above assembly.

Sent from my SAMSUNG-SGH-I337Z using Tapatalk

silence dogood

Active User
H-M Supporter-Premium
Go down to your local bicycle shop and ask them for a old used sprocket the size that you want. They will most likely will give it to you free. Use that as a pattern on I seem to remember 3/16" flat stock. Add chain (careful, there are 2 different widths). Almost went that way, turned out that I could bore out the sprocket to fit the hub that I turned (in this case 1")


Active Member
Active Member
With a rotary table you could mill out the sprocket itself. Even can be done by layout like us old guys use to do. With a couple dowel pins an easy set up to drill the holes to mill the points after .


Active User
Active Member
I remember finding a lot of information about making sprockets and timing belt pulleys on bicycle websites many years ago. But don't know what size chain that is. Maybe 20?


Active User
Active Member
Am I missing something? A bushing will not work? 5/16” will fit into 1/2”? If not, then just make the 1/2” hole bigger. And then Loctite an appropriate bushing. If you are only turning clock hands for a cuckoo clock. Then low torque needs and mischievous accuracy is all you need…Dave