Armed Polite Society
Main Forums => The Roundtable => Topic started by: zahc on May 04, 2021, 07:20:56 PM
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I want to turn the teeth of of a small (13tooth) bike track sprocket with a lathe.
I'm pretty sure they are hardened chrome moly. So they won't turn. Can I heat it up to a certain color and let it air-cool to anneal it? I don't have an oven, just a torch.
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Get a tempil stick for the temp you need to heat it to so you don’t overdo it
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Get a tempil stick for the temp you need to heat it to so you don’t overdo it
Thats the right way but I just heat it up to just red and let it cool off.
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If you do it just right the teeth will melt off and you won't need to turn them, follow me for more tips.
bob
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Depending on the alloy, critical temp is going to be somewhere around 1200-1400F, heat it to that and let it cool slowly, preferably insulated and overnight.
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Just out pf curiosity, why do you want a toothless sprocket?
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I just want the inside part that screws onto the hub. The teeth are 1/8 wide and I need them to be skinny to fit a skinny chain. So I plan to turn a regular sprocket down into a hub then silver braze a narrow 8 speed cog back on. Alternately I could turn the teeth down narrower instead. Or I could have one laser cut.
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What about using a grinder instead of a turning tool? Just go slow. You could still use the lathe to keep it concentric, although it might be easier to grind most of it off freehand.
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I just want the inside part that screws onto the hub. The teeth are 1/8 wide and I need them to be skinny to fit a skinny chain. So I plan to turn a regular sprocket down into a hub then silver braze a narrow 8 speed cog back on. Alternately I could turn the teeth down narrower instead. Or I could have one laser cut.
I kind of thought that would be the goal. My only advice would be the same as Bob's, chuck it in the lathe and use a grinder to evenly take the teeth off. That has the advantage of not having to take the temper out, but doesn't give you as much dimensional control. Good luck.
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Is the quench temperature the same as the annealing temperature? If so, can't you judge the temp is "about" right once the steel loses its magnetic properties?
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Lathe, put something over the ways to catch the debris, and grind with something held in your toolpost. Or, do you know anyone with a milling machine and a rotary table?
And... Look at the Bridgeport Mill User Group on Facebook. When you join it, answer the questions, and tell 'em I said hi from Facebook Maximum Security.