(05-23-2012, 12:31 PM)DanH Wrote: Willie,
Do you still use the different gears or just stick to one setup?
Dan
I still use the gears and the high/low speed ranges (pulley ratio) to set my highest RPM range that is anticipated, and use the speed knob on the VFD to make any adjustments to the spindle speed from there. I know a lot of folks like to select one range and only use the VFD to make all their speed changes.
To me that is fine if you have an inverter duty motor that is built for that. But "overclocking" a standard motor (running it at a higher frequency than what it's rated at) to get to a higher RPM when the lathe is in a lower "gear" is hard on the motor. You CAN run a standard 50/60 Hz motor at 100/120 Hz with a VFD and double it's speed - but it won't last long.
Likewise, having the lathe in a high "gear" and slowing the motor way down to do thread cutting for example - can also overheat it.
I choose not to run my lathe above it's normal 60 Hz, and only use the VFD to reduce the speed when needed. I'm not in a production environment and so hard pressed for time that I can't change a couple of levers or a belt position. I'm only doing it for my own benefit and enjoyment so I tend to "baby" my machines anyway.
So basically I set my gearbox for the high end (smallest diameter), and then slow it down with the VFD to start off with (largest diameter). Then as my stock gets smaller I can increase the speed with the knob, topping out at near 60Hz when I hit the final upper RPM needed to maintain the SFM for the material I'm working with.
I'm not very good at explaining the things in my head most of the time, so hopefully some of that made sense....
Willie