Intermittent z axis problem

[swims@mindspring.com]

I'm getting an infrequent, intermittent z axis problem.

The first time this problem occurred, I was stopping a file by using the 'S' key, and the z axis bound up and I lost my z zero point. I assumed there was something mechanical causing the problem, so I tried putting the z axis through it's paces by using the keyboard commands. No problem moving up or down. I double checked all of the electrical connectors and they all seemed OK. Went through the rest of the day with no problems.

The next day, yesterday, the same exact sequence. I needed to stop a file, hit the 'S' key, the axis bound up, etc., etc.

Could there be something awry inside the ball screw? I've read the thread concerning Z axis creep, but I believe those problems were with Z axes that were shipped with a problem. I've had this machine for nearly two years.

[jkforney]

Steve
When I had my ball screw machine I would get problems with the z axis. All of my problems were traced to dust and dirt. My z axis had a small motor and until I brushed and sprayed a light coat of liquid wrench and then use a large amount of air to clean and get rid of most of the liquid wrench and all the dust, I would continue to lose steps. Of course your machine and shop maybe much cleaner than mine and dust not your problem.

Just before I sold my old machine I started using paint thinner. It seemed to evaporate and not attract so much dust.

For what it's worth.

John Forney

[studebaker]

I also had that same problem at one time. The guide rollers on the Z axis carriage were too tight at the bottom of travel. The edges of the moving plate that holds the tool were not true parallel. Just a hundreth of an inch out. I loosened the V-groove guide pulley just a bit and the Z movement binding went away without any accuracy problems.

[swims@mindspring.com]

The problem did, in fact, turn out to be my ball screw assembly.

I've squirted the ball nut with mass quantities of WD-40 in case there were any rust spots inside, then denatured alcohol to get it as clean as possible, and have now given it a shot of silicone spray (all the while running the assembly up and down). It doesn't bind anymore, but from the way it sounds, I've decided to pick up a new ball nut.

Anyone know what the correct specifications are for a replacement nut? Or, if I'm replacing the nut, should I go ahead and replace the ballscrew also?