Hi!

I’ve got a Sieg C1 micro-lathe converted to CNC already.

I do already have an index on my spindle and PWM control of it’s speed.
As my motor is 150W, and the original pulley relation is 1:2 (4000 RPM goes to 2000), I can do threading ok in plastics.

But when threading metals, even brass or aluminum, at 300 RPM my motor eventually as the threads go deeper it looses it’s torque and speed, misses the pitch and stalls and the motor’s protection overload stops it.

So, I want to replace the original pulleys and belt to a two speed pulley system
I’ve done the calculations on pulley sizes (each one will have two diameters), so at close to the same center distance I’ll have the same 1:2 relation and one 1:6 relation to decrease spindle speed and increase torque, that will be used mainly for threading and maybe parting.

An encoder will also be installed later.

Initially I was drawing the pullleys (motor and spindle) to use a V-belt, Polymax 5M type, which is not synchronized, it’s small (and I have one of these installed on my Sieg x2 mill in replacement of it’s original gears)

I was told by a friend that it would be better to use synchronized pulleys (as the originals).

So now I’m lost. There’s a lot of types of sync pulleys and belts for sale.

There’s the HTD type, GT2 type, XL, 3M, 5M, all with their respective belts.

So I’m lost to which system to go.

I wanted to use a V belt 5M polymax because It’s easier to machine and takes less space on the end of my spindle.

But for the other types, there are already a lot of options and sizes to buy without needing a lot of machining. Maybe only boring to the correct size and doing a keyway.

Can anyone point me which one of these models (to my mini lathe) would be a good cost/benefit? I’m doing this mod to have better torque at threading.

Thanks for reading!

Rodrigo

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