V2-50 Z-axis Motor Stalling

My Z-axis motor is whirring but unable to turn the leadscrew. I do a lot of brass/aluminum/steel.

Two days ago, I found that the insulation was breaking on two of the motor wires connecting into the board (they were smashed by the covering plate). I fixed those two wires. I didn’t see any chips on the board. I then removed the motor from any load, plugged it into the board, and the leadscrew stalls in both directions. I’m able to turn the lead screw by hand when it’s not plugged in and it feels smooth.

I cleaned out the linear guide and nut anyways. Once I reassembled it all, it didn’t work for a while. I kept power cycling it, and it magically worked and I kept machining for ~8 hours with no issue.

I turned the NC on today, and I’m back to the same problem with the Z-axis motor. Any thoughts on what to troubleshoot next? I’m going to keep power cycling it and hoping that it can get me through another part.

So I took the power cord out, let it sit for 30 mins, plugged it back in and powered up. The Z-axis motor is working again.

Any ideas on why I keep having this issue?

That was a good find on the Z motor cable. There are two reasons that the Z axis motor is bogging down. It is possible that chips have impregnated the anti-backlash nut. Everything I suggest from here forward you will perform with the power off and the mini-USB removed.

It sounds like you have already removed the Z axis motor. Remove the silver sticker on the back of the Z axis stepper motor. Remove the Z axis motor again and using a flat bladed screw driver, rotate the lead screw until it separates from the anti-backlash nut. Then using a 2mm hex driver, remove the anti-backlash nut from the Z block by unfastening three screws. Using either isopropyl alcohol or white gas (Coleman Fuel), clean out the anti-backlash nut and the Z axis stepper motor lead screw. Before reinstalling the motor, inspect the rail cover on the Z rail.

Sometimes the Z rail cover can lift up at its ends and chips or debris can build up under the cover, interfering with the Z rail’s linear bearing car. If this is the case, the rail cover can be removed and the rail cleaned by scraping it with a straight razor blade (and vacuumed). Use superglue (we use Loctite 496 here at the shop) to reattach the rail cover. Be prepared with a cloth dampened with isopropyl alcohol to wipe away excess superglue. Let the cover sit for 5 minutes (you don’t want superglue contaminating the bearings in the Z axis linear bearing car. Run the spindle carriage back and forth along the rail. The spindle carriage should move smoothly but you will feel resistance because we put oversized bearings in this linear bearing car.

Reassemble the Z axis stepper motor and jog it back and forth to determine if it isn’t bogging down.

From your last post, it is possible that the Z axis motor might need to be replaced.

Thanks for your response. I will be sure to clean out the nut. The rail cover looks intact.

I think it’s more related to an electronics issue. It seems to resolve any time I power cycle it – specifically taking the power cord out for a while does the trick. I have no issues with Z travel when it’s operating.

If you can repeat the issue, the next time it occurs try this - take off the Side Cover Plate and look at the Main Board. The stepper motor drivers have a red LED indicator that lights when an overcurrent condition occurs on an axis. Look for a lit red LED near the stepper motor driver marked Z on the Main Board. If you do see red LED lit, then it is possible that Z axis motor cable is still shorting against the chassis. This would explain why removing power resets the problem. Let me know the serial number of your machine and let’s see what we can do to fix this problem.

Hi Chuck - Didn’t have this issue come up for the past month until last night. I tried power cycling a few times and no change; kept checking for a red LED on the main board and never saw one light up through all states. I opened up the Z motor wire connection housing, didn’t see any chips or thinned out wires. I cleaned it anyways, unplugged all the cables, and plugged it all back in. Still did not work.

This is crazy, but I moved the X axis about halfway along its’ rail and heard a fritz/pop sound. Suddenly the Z motor was working again. :raised_hands: Any clue on why that would fix it?

SN is 1851A.

Hi Jen,

I suspect that we have an issue in the Z axis ethernet cables that run through the X cable chain. One of the function tests that we run at our shop is is to move the X carriage back and forth while powering the spindle on. If there is an issue, the spindle stalls out at certain points during the X travel.

While the Z axis ethernet cables aren’t the easiest parts to change out, it is something that can be replaced and they aren’t very expensive ($2.94 for the set, you pay more in shipping).

Send an email to service@pocketnc.com and I’ll start a part issue. In the meantime, I have attached a pdf that describes how to replace the Z axis ethernet cables to give you a chance read about how that is accomplished.
Z_Spindle Ethernet Cable Replacement.pdf (643.7 KB)

Let me if you have any questions regarding the cable replacement procedure.