[Farasien]

After Paul left COA its not been as good for service and follow through, but if you can get ahold of the owner, Tony Page, he mostly knows his stuff. His salesman (Jim?) hasn't had good follow through in my opinion.

My COA TK mill didn't have much backlash in X&Y, but Z had some using the weight of the head to take it up. Mine is gone now, but random backlash sounds like bad screws or maybe a few balls all together in the nut that are undersize. Seems odd though. I thought X & Y had a double nut screw. That should make up for a lot. Even a cheap Chinese single nut usually only has about .003 and some much less so it does sound like you have a problem somewhere.

Its not the gibbs. Over tightening the gibbs will kill motors and drivers over time. Even if they seem to be working fine at the moment. I know first hand. On my bigger mill (Hurco KMB1) I set the gibbs by putting an amp meter on the driver power. When current goes up I back it off just a little and call it a day. I run full range of travel and look for tight spots too. They show up really nicely on an analog meter.

Well, I ordered some new ballnuts, and its confirmed its 5x20mm, not the original imperial size I thought. Looking at the screw, it looks in good shape. I bought the mill in 2012 and its seen light use until recently (I was almost exclusively cutting out wood parts). Now, I've been playing more with aluminum and a little steel, so I wouldn't think that worn screws would be a problem. Its always stayed lubed, my feeds were fairly slow and cuts were fairly shallow, so wear is probably not the issue, I would think.

The motor/screw interface is tight, and the nuts at the end of the screw were tight as I could get them without galling the screws (holding so I can tighten).

Any idea where I might get my hands on larger balls for the nuts?