[fejrock]

We have a Bridgeport VMC 760 / 22 that just won't run a full day without some sort of issue. Recently it was experiencing an MO1 overload which after some head scratching turned out to be caused by the operator throttling the coolant using the ballvalve mounted on the spindle. The coolant pump had been recently replaced and was really putting out some great pressure. Unfortunately the job being run required the side access doors be left open (big long part), this got messy. So the operator used the ball valve to bring the coolant flow down to a less messy flow. This caused the pump to draw just enough more amperage that it was tripping the MO1 breaker which was set at 2.0 amps. I have a new breaker which can adjust to 2.5 amps but have not installed it because since leaving the coolant flow at 100% it hasn't been an issue.
This next issue has been ongoing but had been overshadowed by the previous situation because the machine just wouldn't run more than 30 seconds without alarming. This problem seems to involve only the Y axis but there are times when we're not 100% certain of that. The history goes like this; The machine would run fine unless we shut it off at the end of the day, upon start up the next morning the Y axis would be way off (somewhere between .5'' and .625''). So we just didn't shut it off, that worked for a while. Then it began to make noises that at first just sounded like it was making a cut except it wasn't cutting at that point. It sounds like a low growl and is accompanied by a vibration you can feel thru the machine enclosure as well as the floor. I have heard it do it in both the X and Y axis, although to my knowledge it has never lost it's X position. We were having some following error issues but that was related to a poor way oil supply due to a dirty way lube tank. It has now begun to lose the Y position randomly without being turned off. I reduced the max rapid speed from 625 IPM to 500 IPM ( I had seen that solve a noise issue on a BP VMC 1000 a few years ago). I am wondering if the noises have to do with the potentiometer settings for the X and Y motors. I turned the Y-motor encoder a quarter turn to see if that would eliminate the position issue, no feedback on that yet. I welcome any and all thoughts on the subject.

[cncfixxer]

Sounds like you may have an Encoder either going bad or something loose. Indicate the table to spindle backlash and repeatability .... I bet that will tell the story.
Two other remote possibilities ( Does it have a Dx32?) if so check all the connections on the BMDC and look for vibrations on the rack .. maybe debris is getting inside the cabinet.

If it only did it after homing then you have an encoder "Rollover"

[fejrock]

Sorry for the delay in responding, busy week. I am waiting for the opportunity to pull covers and verify that I've got way oil everywhere it should be. With the recent history of the very dirty way lube pump / filter it could be that simple. The noise has evolved into a rumble now. Once the parts that are running in it are done I'm going to be able to get into it deeper and hopefully find the answer to the riddle. Thanks for the info, I will use it.

[fejrock]

Final chapter. Machine was alarming with an axis fault 4 on the X axis. We swapped the X and Y motors, no change, still alarmed on X-axis. We then swapped the X and Y drives, bingo, the error followed the cable to the other drive. When I disassembled the IGUS chain, the wire jacket was completely broken at the rear entry point to the IGUS chain and there were 2 very visible broken wires. This is a mid 90's machine and by all appearances the original tach cable. Pretty good mileage given the environment it has been living in all these years.