Last weekend I bought an old lathe with 20" swing. It came with
a massive 3kW (4hp) 3-phase motor. This draws too much current and
thus I will replace it with a smaller 3-phase motor and variable
frequency drive. I was thinking about to get a 1.1kw (1.5hp) motor.
Would that be powerfull enough for turning larger bowls at lower
speeds?

Frank

Yesterday I went to see a guy nearby here who stocks used and new
motor and VFDs. I bought an 1.1 kW (1.5 hp)(1420 rpm, 3-phase) motor
and the Yaskawa J7 VFD. Both new. Based on the discussion we had and
some posts on this newsgroup it seems that that kind of a scalar drive
can be used to reduce the rpms roughly by the ratio of 1:5 without
loosing much torque. On the other hand the torque will start to
decrease after about 100Hz. That would mean that the workable range
of motor rpms would be 300-2800. With pulley ratios of 1:2.5 and 1:1
I would have two rpm ranges: 120-1100 and 300-2800.

The guy also had a used 1.5 kW (2hp, 700 rpm) motor. I thought that I
would sacrifice high rpm torque with that motor. Am I correct? The guy
said that I can still change the motors. Should I do that or keep the
one I have?

I will go to a shop that sells pulleys tomorrow. If I cannot find the
wright ones from there I thought about turning temporary pulleys out
of birch plywood (and hardening the surfaces by epoxy). I will have
access to metal lathe later on so I could replace them by aluminium
ones.

Frank

personally, I'd go with the higher horsepower. And, I'd see what extra you
have to pay for a vector drive (used, or refurb) - you should be able to get
the drive for under $200, and the motor for closer to $50 (used)


"Frank" wrote in message
...

Yesterday I went to see a guy nearby here who stocks used and new
motor and VFDs. I bought an 1.1 kW (1.5 hp)(1420 rpm, 3-phase) motor
and the Yaskawa J7 VFD. Both new. Based on the discussion we had and
some posts on this newsgroup it seems that that kind of a scalar drive
can be used to reduce the rpms roughly by the ratio of 1:5 without
loosing much torque. On the other hand the torque will start to
decrease after about 100Hz. That would mean that the workable range
of motor rpms would be 300-2800. With pulley ratios of 1:2.5 and 1:1
I would have two rpm ranges: 120-1100 and 300-2800.

The guy also had a used 1.5 kW (2hp, 700 rpm) motor. I thought that I
would sacrifice high rpm torque with that motor. Am I correct? The guy
said that I can still change the motors. Should I do that or keep the
one I have?

I will go to a shop that sells pulleys tomorrow. If I cannot find the
wright ones from there I thought about turning temporary pulleys out
of birch plywood (and hardening the surfaces by epoxy). I will have
access to metal lathe later on so I could replace them by aluminium
ones.

Frank