Thanks guys. I just landed in Houston Texas a few hours ago so now I am counting the days )
I am investigating the VFD route to replace the variator and joined the yahoo group for Holbrook lathes. I am not sure I understand why there would be a problem using a vfd regarding torque if you have a gearbox that has 2 speed ranges - first gear for threading that is 80 - 500 rpm, and the second gear 500 - 3000 rpm.
The motor is connected to the variator and runs at full rpm - the speed is adjusted at the variator which is then connected to the 2 speed gearbox - the gearbox then turns a pulley belt that heads up to the headstock.
To proceed I would need to know the ratios that the gearbox provides in order to figure out if the VFD is the best option or if I should go with a DC motor. Am I on the right track here?
Paul.
Thanks for the input Uncle Harry. My only concern is that even with a constant torque VFD, when I reduce the RPM it will still have reduced torque and I need to find a good solution to this.
At 1440 RPM, the motor is putting out 3 HP, so at 720 RPM through a constant torque VFD, it is putting out 1.5 HP. I need to know what the gearbox range is so I know how to go about using the VFD. The solution may be using a constant torque VFD and having a 2 speed gearbox between the motor and existing gearbox. The lathe has electrical actuation of the existing box and I am sure I could couple the intermediate gearbox to the same electrical system to allow electrical actuation of it too. This would mean that the low range would be reduced by gearing down the motor twice through 2 gearboxes and then having the fine control via VFD to reduce torque loss.
Unfortunately I can only speculate at the moment because I don't know if the variator increases output RPM past the motor's RPM, or what the gear ratios are for the gear box, nor the pulley sizes from the gearbox to the headstock. There are 3 seperate torque and RPM affecting units here that act together and I am not sure where to start at the moment.
Paul.