Time for my annual request for help from the forums to troubleshoot the next new problem with my machine.
My Sabre 750 had been sitting for about a week when I went to run it today. I have a spindle warm-up program that steps the spindle up slowly from 500-2500rpm, and all seemed good on that. But when I went to run a program, things took a turn for the worse.
The first tool was a .750" end mill at 7500rpm. As soon as the spindle started to turn, there was a shuddering sound coming out of the spindle head. The best way I can describe it is it sounded somewhat like a power saw coming to speed while cutting wood. Once the tool got to speed, it ran OK. But when the spindle turned off and began to brake, it gave a similar but less loud shudder. When the next tool loaded and ran to 8000rpm, the same thing happened. So I shut it off, with the same shutdown shudder. My first thought was that the spindle had a bearing going bad. But turning the spindle by hand, and it all feels like butter. I really don't think this is a bearing issue.
So I shut it down and pulled the cover. I couldn't see anything obvious, so I rebooted the machine to move the X up to get a better view. When I restarted it, I could hear a buzzing sound coming out of the spindle. With the spindle off and when I grabbed the spindle, I could feel that the motor was actually driving to this ugly intermittent signal. The spindle was chattering back and forth in my hand. Not with enough force to really move the spindle, but enough to feel it with your hand. So I immediately shut it down.
After this bit of diagnosis, now I suspect that this is actually a spindle drive problem, and not a mechanical issue in the spindle head. There were no error codes given ,and everything int he cabinet showed green. Does anyone have any thoughts or ideas on this one? As a note, the spindle drive is the only one of the five boxes in the cabinet that have not been replaced by me in the last 5 years.