I'm looking at buying an older series I bridgeport and I have a few questions. First off, I've noticed that the J-head machines tend to be considerably cheaper than the 2J heads.
If I'm correct, you must manually change belt positions on the J head, and the 2J has the adjustable knob with a Hi and Low range, right?
I don't have 3-phase available, so I will need a phase converter. I've heard that you can vary the speed of a 3-phase electric motor with a VFD, so I stumbled across
the Mitsubishi S500. Does that look like it will work?
I've heard of the ability to "overdrive" motors if using a VFD like the S500. As I understand it, if I run the VFD at 120 Hz, the motor will be spinning twice as fast as it was designed to, right?
Can a Bridgeport motor handle this? Does this damage the motor or any other part of a milling machine?
I'm thinking about getting a less-expensive J head bridgeport, then and using a VFD to do most of my speed changing, leaving the belts in one of the higher gears. I mostly cut aluminum, so I believe this should work, and if I have the ability to overdrive the spindle, that would be great! If I'm correct, the maximum (standard) spindle speed for J heads is 2720 RPM. 5000+ RPM would definately be nicer for aluminum!
Feel free to correct me if I'm wrong, offer me advise, or point me in the direction of good, inexpensive milling machines and VFDs.