Bpt Series II J head not spinning

[scmw]

Hi Guys,

Of course, it always happens at the end of a project with one last series of parts to make. One of my Bridgeport Series II NC's (I have two identical units) is having a problem starting. Both run Mach 3. This mill was running at about 1200 RPM on the spindle and I started dropping the speed as I'm cutting some thin styrene plastic. Unfortunately the spindle slowed down and froze. I've tried to restart it but just get the three phase hum for a few seconds before I shut it off. I am going to try loosening the belt to see if it's a mechanical problem or if the motor might have finally given up the ghost. This particular unit is from the 1970's.

Has anyone else had a similar situation? If so, how did you go about fixing it? If the motor did die, would this be a situation where a VFD could be put in it's place? Both mills have 4HP GE motors.

Thanks,

[scmw]

OK, we just figured out part of the problem. Thankfully it is NOT the motor. We backed up the spindle and worked the speed control knob on the upper right of the head back and forth. Getting it to the slowest setting is a real bear. The speed knob rotates smoothly from 1000 RPM and higher. We rolled it up to 1200 RPM and tried the motor a couple more times. She finally broke loose and started spinning. After playing with this a bit more, we've come to find that the brake is binding below 1000 RPM.

Anyone have any experience with brakes on Series II machines?

In the meantime, we're adjusting our CAM for the parts due to the higher speed RPM. Cutting is going well but I need to figure out a solution for lower RPM's.

Thanks,