New Z Axis problem

I was so happy, everything was working great and then … My Z axis suddenly started acting very badly.

I have a 500mm X Carve (upgraded from SO2) with the ACME Rod

If I try to move it in increments of more that .4 mm is stalls and the motor will not turn. If I set the increment to .1 mm it seems to move fine (but it sounds different than it did)

When a movement greater than .4 mm is attempted the motor sounds like it is bound and cannot turn, but if I try to turn the ACME rod by had it moves easily

Here is what I have found through trouble shooting

  1. I can turn the screw by hand with ease (even when the motors are powered up)
  2. If I turn the Z micro pot on the Grbl board clockwise it seems to move better but even at full rotation it does not move correctly
    3)I have loosened the eccentric nuts (very loose) and the problem not change.
  3. I have the fan mounted on top of the electronics (blowing into them), but the problem does not seem to be heat related.
    5)I have checked the set screws on both of the pulleys and they are tight, the motor shaft and ACME screw shaft are not slipping.
  4. The X and Y axis are working fine
  5. I tried measuring the voltage from the Grbl to the motor but using a multimeter was not very helpful, the voltage changes so quickly. I guess I would need an o scope to see anything meaningful

It is almost like after the last run the Z motor lost most of its torque.

Not sure what my next step is.

  1. I can turn the screw by hand with ease (even when the motors are powered up)

If you can do this, you may have bad connections somewhere, or your current pot is set much too low.

  1. If I turn the Z micro pot on the Grbl board clockwise it seems to move better but even at full rotation it does not move correctly

There is only one, “good” position for the current pots on the grbl board. Both too high, and, too low are bad.

mine did something similar to that and i had a loose wire

Thanks, It seems like a bad connection must be the issue. I will recheck all the Z connections again tonight.

hopefully it is something simple like that!

I looked closely at the Grbl shield and noticed that the connector block for the Z axis is in two pieces (2 wires in one part then two wires in the second part). The X and Y blocks are one solid piece.

Is this normal? Or did the Z axis connector block break and that is what is causing my problem?

are you talking about the green connectors in this picture?

Yes I am. On my Z connector (the far left one) there is a visible crack between the second and third screw.

Oh yeah that doesnt seem right. You should take a picture and email the help line

Good idea

Have you checked the belt from your motor pully to the ACME screw?

Yes it is correct.

Here is what the connector looks like, I have sent an email to with the details.

That just looks like two doubles improperly connected to each other.

It doesn’t mean anything wrong. Just a connector is two pieces, but did you check solders on other side board to see if any crack solder or anything moving on solders pins.?

@AlanDavis - I think you are correct, I checked the solder connections under the board for the connector and they appear solid and nothing is moving. Also if I look closely at the other connector blocks I see that they are also comprised of two blocks, they are just much closer together.

So I am still left with the mystery of the non functional Z axis. It is still working fine as long as I make tiny steps of less than 3 mm, anything larger and it just hums.

I will move the z motor connections to the X and see what happens.

It is possible that you could have a weak solder joint. If you have a soldering gun handy, you might disconnect everything and try reflow some solder on the bottom pins for those connecters. High heat will be your friend here.


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@JohnScherer - Good thought, I checked the solder connections under the board again and they are very nice machine soldered connections. I checked the continuity with a meter and they are very solid.

I removed the Z motor from the mount and held it while Easel stepped it. I found that I could easily keep the motor shaft from turning just by holding the shaft between thump and index finger. It seems to me that the motor should have much more torque than that.

So reduced torque can be a wiring problem, Grbl shield problem or motor problem. I connected the Z motor to the X connectors on the GRBL shield and it behaved the same, so I will assume the GRBL shield is not the problem,

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That’s some top-notch debugging there. I bet if you update help@inventables they’ll get you a new one asap.

I have not heard anything back yet from the help email at Inventables so I will ask here. (I really need to get the machine operational again)

With the NEMA 17 failing on the Z axis (or at least that is what I think happened) I need to buy a new stepper. My question is should I go ahead and purchase a NEMA 23 for the higher torque to prevent a future failure? The cost difference is not very much and I would prefer never having to worry about the motor failing again.

I assume that I can just swap out the NEMA 17 for the 23 (changing the pulley also) and everything will work normally without needing any config changes for the controller, I also assume that the GRBL shield can provide adequate power for a NEMA 23 Z and NEMA 17’s for the two Y and one X motors.

It seems odd that the Z would be the motor that needs more torque (I would have thought it would be the X) but that is what my machine seems to need.

A heads up if there is anything else I should consider would be most appreciated.