Thread: Making Gears

Hi Chris,
Just to be clear, your talking about making a sprocket for a chain, is that right?

Ew

Yes.

It could be done,
Is there any reason you are not just buying commercially made items?
Or are these something that are not available or too costly?
What sort of turn around time frame are you looking at?
As I am still 2 or 3 days from getting my big mill going again.

Matt

I can probably put you in contact with someone who was nearby, but may be up the coast now. He did split sprockets for a supersport race car, that weren't readily available commercially with the PCD required. Dunno if he'd be interested, as the impression I got it was pretty tedious work, cranking the dividing head ~ at least in the 40+ tooth range and the inevitable FUs along the way when the count was off.

Form tool used was for 530 chain, so you'd be up for a new one of those, before you start. 415 for a superkart even if a 125, seems a touch adventurous, I would have thought!

Learning something every day
For a simple item, they look to be much more complex than their appearance would suggest. Based on a quick web search, either 7075 Al or something like a hardenable steel (CrMo?). Heat treated after manufacture. Can be drilled/milled but hobbing seems to give a more accurate profile - although in this day and age a CNC machine if programmed correctly should be able to do the job.
I second Matthew's question - is there a reason you can't buy them? I suspect that there is a learning curve before you arrive at the optimum manufacturing method and H/T combination, so homemade versions may cause frustration on race day until it is right.

Michael

The equivalent race bikes use 415 and as the motor is a 125cc and hasn't got enough horsepower to get out of its own way we want to go to a lighter chain. I can get the front sprocket OK but the rear has to be made due to everyone else, ourselves included using a 428 up to now. The 428 sprockets used to be made in SA but that has ceased due to the person retiring so there is a need for them as well. It is not quite as simple as a one piece gear, they are a split gear which sits on a carrier, the axle has to be removed to fit the carrier and then the gear can be fitted very quickly without removing the axle. I can get what I want made locally but I thought that I would offer it here and someone might like to make a few dollars. I realise it is a complex thing to make and was never under the illusion it was not going to cost dollars so I am not asking for any favours. There is a market for the ongoing supply of 428 gears and I can sell those or tell others where to buy them, the 415 is a one off for me and most probably won't be repeated.

Hi chris, im always looking for new products to make. Can you send me a sketch with some rough dimensions so i can see if they can be made with my tools?
They would be cnc milled and no doubt turned as well

Reason for the doubt on the 415, is even mini bikes/cycles in my day specced 420, 125s 428. Contact patches on a kart and the scrub required to get around a corner has me thinking there's a reasonable difference there, also remembering a mate who died at OP in a 125 superkart in the late 70s - that thing did have some mumbo!

I did give my guy a call, he's been forced out of retirement post gfc, not interested in doing that stuff though - one run was enough it appears. He suggests he'd have them laser or water jet cut now - or if made of money, wire cut - and then finish the tooth profile in the lathe.

Honda's spec on the chain is 415 for the bike and I too have my doubts. The other person involved in this has done it before with no issues so we thought we would give it a go. Our chassis set up means there is very little scrub coming off corners like others experience but I know exactly what you mean.

Did you end up getting some sprockets? I am also after some 415 sprockets for a kart.