Masterwood 280 x axis locking up

[QuinnSjoblom]

We have an mw280 in our cabinet shop that is having an issue. Yesterday it stopped suddenly and gave an x axis fault, noticed an af1 (lost 1 input phase) error on the yaskawa drive for x, tracked it to a blown fuse on one leg of drive. Replaced fuse, machine fired up without error. We cautiously started slowly jogging x back and forth and could hear the servo struggling. While jogging it will free up, then suddenly bind again. I've confirmed it's mechanical by powering the machine down, crawling underneath, and turning the ball nut by hand (fixed screw, turning nut setup). It's a big gantry, but when it's not locked up, I can turn the nut by hand without much effort. When it gets to a position where the servo struggles, I am not able to turn the nut by hand with the machine powered down. I think it's safe to say something is mechanically binding up. Since this is a fixed non rotating screw setup, the ball nut assembly is mounted to the gantry with a pair of bearings. To me it seems that this binding could be happening in either the ball nut itself, or the bearings that mount it to the machine.
Does anyone have any advice on how we should move forward with this? Based on the behavior, what is the most likely culprit? If it is the ball nut binding on the screw, why is it locking up only some of the time and then freeing up? When it does lock up, backing up in the opposite direction then feeding forward again seems to free it up. Maybe the balls are getting stuck as they circulate through the nut? What would cause that? Any advice appreciated

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[Jim Dawson]

I think that your guess is correct. Maybe a broken ball? My mill has a tight spot every 5th revolution of the X ball screw, but doesn't lockup tight.

[ger21]

Try cleaning all the grease and dirt out of the nut, and re greasing it.

[QuinnSjoblom]

We may have found the issue but I'm not positive yet. This particular ball screw has a grease fitting on the nut for lube rather than the automated oilers like on the y and z axis. It was probably about due for it so we gave it a squirt of grease and jogged it back and forth to see if anything improved. It did seem to help. I looked underneath and after doing that, the screw had a gummy residue on it, literally about like the consistency of gum, mixed with some of the new grease we put in. I think the shot of grease pushed out some of the old stuff that was gumming up for some reason. Maybe a lube incompatibility issue in the past or just went too long without grease. After seeing the gummy residue, I spent the last 2 hours cleaning the screw off with alcohol, oiling it, jogging again, clean off new layer or residue, oil, etc. Did that a few times until there was no more residue left behind and it now seems to be running quite smooth. Machine is cutting a nest now. For now I think we will continue to just oil it often instead of grease and see if it acts normal for the next few jobs. Hopefully the gummed up lube was the issue. Need to figure out what happened with the lube, find out exactly what type of grease it needs, probably thoroughly flush out the nut before adding any to make sure we dont have compatability issues

[QuinnSjoblom]

Ha! I posted right before you Gerry, but you pretty much nailed it

[ger21]

Our Morbidelli calls for greasing the nut every 40 hours or so. If you don't, sawdust can build up inside. The grease flushes it out.

[QuinnSjoblom]

Good to know, I'm not actually the operator but since I somewhat know my way around machines now after building one, I was able to help him diagnose.