[How-To] Figuring out speeds with pulleys on a lathe

[Ben17484]

Really basic question but I’ve just got my first lathe that has speed control via pulleys and reading the data plate doesn’t make sense to me. The motor has two pulley sizes on the motor end and the pulley assembly (does this have a proper name?) end. There’s 4 combinations already. There are 4 pulley sizes in the head stock and 4 at the pulley assembly end and then there’s direct drive and with back gears.

My data plate suggests there are 16 speeds, but with the combinations I can see from what I’ve posted above, I’d have a lot more, wouldn’t I? I’m assuming High and Low are the motor speeds, direct and back gear i get, but I’m getting confused as to where the belt needs to be on the pulley assembly at the back and where it needs to be in the head stock to achieve the speeds on the data plate?


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[pontiac428]

You have four positions on your direct drive sheaves times the two positions on the motor sheave, that's 8 speeds, and the back gear makes 16. The sheaves are paired, you can't criss-cross without changing the belt size.

Lathe speeds don't need any type of fine division, even big commercial lathes often have no more gear range than this.

 

[Ben17484]

You have four positions on your direct drive sheaves times the two positions on the motor sheave, that's 8 speeds, and the back gear makes 16. The sheaves are paired, you can't criss-cross without changing the belt size.

Lathe speeds don't need any type of fine division, even big commercial lathes often have no more gear range than this.

I see, so the position on the head stock matches the position on the pulley assembly I.e second from left on the headstock has to go to the second from left on the pulley assembly. That makes sense. Thanks.


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[pontiac428]

Correct. It looks like your motor and drive set is mounted some distance away from the back of the lathe (compared to stock, I assume), giving more room to criss-cross belts. The Atlas has big bevels in the sheaves to allow some criss-crossing, yours look pretty tight in comparison. I think these light lathes prefer to get every bit of their half horsepower transmitted to the spindle from running the belt straight, any crossover will get the friction going.