So, my stock .75 HP motor in my 9 x 20 Lathe bit the bullet, I'm upgrading to to a 2 HP motor and I can't seem to find a "Rule of Thumb" of belt size to HP ratio formula, (understanding the pulley depth\dia. will have to change too).
The idea is, the new motor will also be VFD controlled, and as such, yes I can control the 'Start-up-to-RPM' and 'Coast-to-stop' and I could actually use the .75 HP rated belt I have.
However, if I want to set my E-Stop to 1 second stop (with a resistor pack) and not the normal Stop button, how do you figure out how big a belt you need to handle the 'Shock Load' of a sudden stop?
Thanks for any help.
Chazz
Hi Chazz,
Good question.
FWIW, I have just replaced the single phase 550Watt, 1500RPM motor (0.75HP) on my 9 x 20 lathe with a 550Watt, 1500RPM (0.75HP) 3phase motor and VFD. I did consider putting a larger motor on but decided against it as the original motor comfortably handled anything I ever threw at it.
I can't imagine wanting to machine anything that would require over twice the grunt of the stock motor, I doubt that the lathe itself is big enough or sturdy enough to go nuts with it. So, do you really need 2HP? Given that you are considering (2?) new pulleys too, it seems like a lot of work for no good reason, even if you stick with the old pulleys you will need to bore out the motor pulley to accept the much bigger motor shaft.
However, if you did go for 2HP I'm sure that the stock 9 x 20 toothed belt (provided it's tensioned correctly) will handle it fine, how often would you be hitting the E-Stop anyway?
Those belts are plenty strong, both my belts handle an E-Stop with no problem, but buy a couple of spare belts if you are worried about breaking one, they aren't expensive.
One more thing, a 2HP motor is physically much bigger than a 0.75HP, installing that so that pulleys line up etc will be a pain.
Good luck.
