Split Sprocket

[Brad93]

I need to make some large split sprockets.

So i can either buy platewheels or pilot bore sprockets. Either ways during cutting in half material is lost and the trough radius would not be right, if pilot bore the bore then isn't round and undersized.

How is this done in practice? Two platewheels to make one seems like a waste.
I need split sprockets with bores from 125mm up to 215mm.

Or one big sprocket with 215mm bore and then split inserts to bring the size down.
Again split inserts. Do you split a ring, bolt back together then finish machine the bore?

 

[Ton-up]

Cant you buy them Brad, my mate bought one last year for his train about 350mm dia. Ill ask him tomorrow where he got it but I believe Essex Bearings got it for him.

 

[Maker]

Split it and then weld some material on to make up the kerf? It only has to be half an inch or so at each end of the cut and then file it to match the profile of the tooth.

 

[Munkul]

Rough them out with plenty extra meat, split them, bolt together, then finish bore and profile the teeth. It's the only way, unless the kerf gap is acceptable...

 

[Brad93]

Rough them out with plenty extra meat, split them, bolt together, then finish bore and profile the teeth. It's the only way, unless the kerf gap is acceptable...

i think it's a job for a cnc

 

[Rrobson]

Edm? You can get wire size down to 4 thou, I don’t know what the actual cut width will be but would a couple of thou be noticeable?

 

[Agroshield]

I do not think a small gap the kerf of your cut in the root of the tooth is going to make any difference to the performance of the sprocket. You could cut most of the split with anything (wobbly torch if necessary) and finish off the last 10mm either end with a junior hacksaw. Clearly, if the sprocket has an odd number of teeth, the cut cannot be across a diameter if it is to coincide with a tooth root each side.

Cut a large washer on the plasma. Bolt it to the uncut sprocket. Drill and roll pin in two places each quadrant (8 pins total). Remove and chop the sprocket in half. Chop the washer in half 90 degrees to the sprocket cut. Reassemble and everything will be aligned.

Look at a used sprocket. I do not think there is any contact between chain and sprocket at the tooth root - it is a clearance area. On my bike, the paint is rubbed off about halfway up the sprocket tooth (analogous to the pitch diameter of a gear). You can check this on the confuser: download sprocketeer, which will give you a dxf of any sprocket you want. Generate the sprocket and then dimension the root radius it produces. See if that number matches the roller diameter of the chain.

Depending on the shaft diameter and space available, you might get away with a single split and spring either the sprocket or the washer (which can be made from much thinner stuff than the sprocket) or both over the shaft.

Cat D8's seem to manage with gaps in the tooth roots:

 

[Brad93]

I do not think a small gap the kerf of your cut in the root of the tooth is going to make any difference to the performance of the sprocket. You could cut most of the split with anything (wobbly torch if necessary) and finish off the last 10mm either end with a junior hacksaw. Clearly, if the sprocket has an odd number of teeth, the cut cannot be across a diameter if it is to coincide with a tooth root each side.

Cut a large washer on the plasma. Bolt it to the uncut sprocket. Drill and roll pin in two places each quadrant (8 pins total). Remove and chop the sprocket in half. Chop the washer in half 90 degrees to the sprocket cut. Reassemble and everything will be aligned.

Look at a used sprocket. I do not think there is any contact between chain and sprocket at the tooth root - it is a clearance area. On my bike, the paint is rubbed off about halfway up the sprocket tooth (analogous to the pitch diameter of a gear). You can check this on the confuser: download sprocketeer, which will give you a dxf of any sprocket you want. Generate the sprocket and then dimension the root radius it produces. See if that number matches the roller diameter of the chain.

Depending on the shaft diameter and space available, you might get away with a single split and spring either the sprocket or the washer (which can be made from much thinner stuff than the sprocket) or both over the shaft.

Cat D8's seem to manage with gaps in the tooth roots:

View attachment 372184

shaft diameter is 215mm

 

[8ob]

The only split sprockets I have seen worth a rub came with a separate split hub and sprocket, the two halves of the hub were held together with a couple of recessed allen bolts and the split sprocket bolted to the hub @ 90degrees so they effectively held each other together. I would have thought making a split hub would be straight forward, buy a sprocket and cut it in half, if the hub has a good diameter register/shoulder the sprocket will remain indexed irrespetive of the split/cut width.

Bob

 

[m_c]

I was curious about this, but that Martin's catalogue gives you next to no information about them.
From what I can figure out from the catalogue, the hub and the sprocket come separate, but it gives no indication on how they get combined.
I'd doubt the plate/hub get machined from solid, but it would be possible.

Given modern CNC capabilities, it would be entirely feasible to machine the two halves from solid, and end up with a perfect pair, and if the bore was needed to be critical enough, finish bore it with the two parts clamped together.

However, I do wonder if they simply leave a gap all the way through so it will still clamp a slightly undersize shaft, but as per @80b 's post, having the parts separate would give a better fit.
It'll all depend on the application.