I have the 3 phase option for this lathe and decided to make some changes to the controls when hooking up to the VFD. The first thing I did was mount a junction box to the side of my stand so that I had access to it without having to move my lathe or leave a lot of room behind it.
I have a lot of experience with VFDs and industrial controls, so decided to try some options to see how I would like to use my lathe. I had a Teco CV7300 VFD already on hand, so used that. It has PLC capabilities, but I need a special programming cable, so I am not using that yet, but might in the future. That would enable me to add more features without having a lot of relays in a junction box, and I could change how it works without any new hardware.
I have a 24v power supply in the VFD panel that supplies control voltage for the machine forward/reverse and power outage circuit. This circuit controls relays for the VFD controls. I have a power outage protection relay controlling power to the forward and reverse relays that provide signals to the VFD. This relay cuts off the 24DC controls power from the VFD until the relay is energized. When moving the lever to forward for example, the forward relay is energized giving the forward signal to the VFD. I have the pilot light on the lathe wired so that it only goes on when the protection relay is energized. This way I know at a glance if the machine is ready for operation.
I mostly make things in metric so I wanted to find options for threading while keeping the half nuts closed. I like the idea of the proximity switch to thread fast and have it shut the motor off at a predictable position, but I got to thinking about speeding up returning to the thread start since I will not be able to open the half nuts to return to the starting position. So, I installed a switch that sets the VFD speed to 50% for threading as well as setting a fast deceleration time of 1 second, and a bypass button to return the VFD to full speed when I want to reverse to the thread starting position. I can set the gears to any speed I want knowing threading will be half that speed when the switch is enabled, and at the rated speed when reversing. It speeds up threading a bit, but does take some getting used to.
I did not install a jog button and so far I don’t miss it. I have the VFD programmed for a 5 sec ramp up and use the fwd/rev lever to bump the position if I need to. I haven’t done much with that yet, so may need to change that at some point.
I plan on adding a proximity stop at some point. I already have the sensor from a previous project, just need to make a bracket for it. I think that might work well with my rapid reverse, use the push button to bypass the prox switch and fast reverse at the same time. I am also going to add a DRO at some point and have been thinking about what I would need to have a constant SFM feature. I haven’t added a potentiometer to vary the speed of the VFD yet, if I add the constant SFM feature, I will probably add the pot into that, but I haven’t really needed that yet. If I need speeds in between that gear speeds, I may be able to set my threading switch to half speed and select a speed that may be more appropriate. I haven’t done that yet, so don’t know if the reduced power is going to cause problems.
Anyways, that is where I am at with the controls and expect this to evolve over the next several months. I may not stay with how I am doing things now, but I am enjoying experimenting with different options and see what works best for me.
