Z-axis binding when homing and during operation

[Richard Gretz Goldsmiths]

So we've got a strange problem where the z-axis seems to bind at certain points and lose its home position.

Manually moving the axis doesn't seem to cause the problem, but it's happening fairly consistently everything time we home the axis, as well as during operation.

We only use the machine to mill wax, and we've thoroughly cleaned the rail and lead screw.

Do we need to take the whole axis assembly apart and clean/regrease the bearings?

Thanks for any and all input!

[qrot...@pocketnc.com]

Hi Richard,

Sorry to hear that you are experiencing some trouble with your machine's Z axis! I would be happy to help you troubleshoot the issue. 

Please reach out to us a ser...@pocketnc.com when it is convenient for you and we can discuss the issue and troubleshooting steps in more detail. 

Thanks,

Q Rothing 

Applications Engineer, Pocket NC 

[Richard Gretz Goldsmiths]

We actually figured it out!

The machine we had purchased was a demo unit, so it had been used to mill aluminum in the past. The bearings were pretty full of little bits of metal that aided in the binding issue.

Took the whole assembly apart (not the hardest machine to work on, but there was still a bit of cursing while trying to get to some of the screws), cleaned the bearing really well, as well as removed the thin metal cover on the slide. 

We found that the metal cover was putting positive pressure on the bearing plate, making it very difficult to move, particularly on the ends.

With that removed, the slide was cleaned and gently honed with a sapphire wet stone, the bearings repacked with grease, and the machine put back together.

Now it works great....almost.

In the process of moving it around and disassembly, we knocked the x-axis out of home somehow. Had to research how to actually change the home offset, and then develop a millable calibration part.

So after all that, it's working great once again!

[qrot...@pocketnc.com]

Hi Richard,

I am glad you got the issue resolved. The process you went through is very similar to what I was going to suggest. The one thing I do want to warn against is running the machine without the Z rail cover. Without that cover, chips can accumulate in the heads of the fasteners and then get deposited into the bearing car as it passes over the fasteners. Is your cover still in good shape (not bent or torn, etc.)? If so, it can be scraped clean and re-adhered to the Z rail without much trouble using a low viscosity adhesive (we use Loctite 425). If your cover is in rough shape, let me know and I can ship one to you. 

Thanks!

Q

[Richard Gretz Goldsmiths]

The cover is still in good shape, but we aren't too concerned about the accumulation of debris. We only mill wax with it, and vacuum the wax out before, during, and after each milling job. We are still monitoring it though, so I doubt we'll have any issue.

My concern with re-attaching the rail cover is that I believe the rail itself would have to be ground maybe half a thousandth of an inch, or else there is too much resistance against the bearing car, making the motor work harder than it needs to. We did notice the z-axis motor getting warmer than the others, and since the removal of the cover, it now runs the same temperature as the other steppers. So for the time being, we'll just continue to keep it spotless.

Thanks so much! 

[qrot...@pocketnc.com]

Sounds good! If you decide that you do want a cover, let me know and I can send a thinner one. Otherwise, I agree, I think keeping your machine nice and clean will work just fine. 

Happy machining!

Q