mrt1723 said:
I have a DC motor I was going to put on my 8x12 but I like your VFD idea a lot better. Can you tell me a little more on what motor you used and what VFD you used ( I can see that the VFD was a Allen Bradley but what model? Also the price would be nice on the motor and VFD.
I plan to CNC my lathe soon.
I was hoping to get more ideas from Bob's web site but he seems to be dragging his feet a little.
The VFD is an allen bradley 1305 VFD. It's an older one. The motor is just a standard 208 V 3 phase motor.
The beauty of the VFD over DC motors is the speed regulation over a wide range of loads. A dc motor at low speed will slow badly when loaded up (no torque). An AC motor, while it produces less than full torque at the lower speeds, still has a fairly constant speed from no load to full load. VFD's can also be programmed to compensate for loss of speed due to load so if you want 400 RPM at the spindle, thats (roughly) what you get regardless of depth of cut etc.
Basically the speed of the motor is tied directly to the frequency of the output of the VFD, regardless of the load.
I teach electrical at a college. Industry donates a lot of thier surplus equipment to the college. Some of it is used to build demos itc, but sometimes there is just too much stuff to use. This VFD and motor was available, so I asked for it. In return I plan on building an "open" electric DC motor from scratch for demonstration use at the college. Large enough so it's possible to see what's going on as it operates. That is my next project but I wanted the lathe updated first to make the build easier.
VFD's can be had on ebay, so can 3 ph motors. Just make sure they are compatible in HP and voltage, and if 3 phase input, make sure it can also be run on single phase. Ideally, if run on single phase, the drive should be rated 150% of the motor HP. This is not a must, but be aware that if you run a 3/4 HP motor on a 3/4 HP drive that's run on single phase input instead of 3 phase input, you will only get 1/2 HP out of that 3/4 HP motor.
Hope that helps.
Eric
Eric