[Nick90]

Hello fellow ShopSabres,

I was wondering if anyone else has been experiencing the same problem I have. I haven't had a consistent Z-axis since we have owned the machine.

My manufacturing involves a lot of precision depths, so this is a crippling problem for me. I was on the phone with Ben for a couple hours last week and we thought the problem was with the tool touch off pad, but now I know there's something else going on here.

For example:
I will bring the bit down the the table and set the Z at the surface. Later, when I bring the same bit back down to the same spot, it will be up to 0.030" off. It's the same problem with all 10 tools.

I'm thinking now that it must be some problem with the hardware. Or could it be my air supply?

This inconsistency is always changing and is unpredictable. The ShopSabre guys seem as stumped as I am. Haven't been able to make any progress with this problem yet and it's really hurting my business.

Has anyone else had to deal with this? Any advice is greatly appreciated!

Thanks again,

Nick

[rgh]

My first guess would be hardware as well. The Servo motor not catching all the signals, or they aren't being sent. A slow (or non-dedicated computer) might do this, but since it is only the z axis, I wouldn't think so. I don't think the machine controller handshakes with the computer card to detect dropped signals, so if a signal gets missed it would result in the servo going out of sync, but I wouldn't think the card in the pc would differentiate between z,x, or y. So, I wouldn't think it would be the card set in the pc. Any common circuitry in the controller would be ruled out for the same reasons. I guess if the air balancer was out or sticking...maybe, but I would think the controller would catch that and give an error.

If the servo controller module in the control box doesn't send a signal every once in a while, the machine would go out of sync as well. Since it is only the z axis that is having the issue, it points toward the z servo controller. Might check with Ben to see if the servo controllers can be switched (y or x for z) to see if the problem follows the controller. The other thing would be a wire or loose connector to the z servo, though I would think the variance would be more severe and random than a couple hundredths of an inch. Putting a temp cable in for z would test that out, but my bet would still be servo controller module. Might also check to see if Ben has any tests for the z controller signals that could be captured by the pc and reviewed when you lose sync (to ensure all signals were sent. It would tell if the servo motor was the problem.)

[Nick90]

With the help of some users at the Vectric forum and Ben at ShopSabre, we have discovered the issue and created a (temporary?) fix.

It turns out that the ball nut on the Z axis was actually turning in the holder at certain times (as suggested by a Vectric forum user.) This was causing the machine to lose the intended depth. We marked the nut and holder to observe its position. Sometimes the nut would turn about 1/8-1/4 turn in the holder, accompanied by a clunking sort of sound. This would usually happen when the spindle reached the top of the Z axis and sometimes at the onset of movement on the Z axis.

It's difficult to access the nut inside the spindle assembly. First ShopSabre recommended that we take the spindle off the machine and use Loctite to prevent the nut from turning (also what the Vectric user said that he did for his SS machine.) However, I didn't feel comfortable doing that at this stage. SS explained they would walk me through the process and even provide pictures on the proper way. SS then recommended that we could try pushing on a steel block on the nut that we accessed from the right side of the spindle. We were able to tighten the nut. I haven't run any production yet, but have done several small projects and it looks like it's secure so far. I'm curious to see if it stays put during production. It might be necessary to take the spindle off and Loctite as we were first advised.

Will update again with any new news. Thanks for the hep everyone!