Z keeps getting deeper and Deeper

I have an issue where as I set zero on the Z axis but as the project runs the z keeps getting deeper and deeper even though the G code is not telling it to. I have put index marks on the shafts and motor to verify the coupling was not slipping.

Tell us about your set up. Are you using the stock Z axis? Have you tried the cheap fixes for z axis slop?


I have just really started trying to use it. But I built my frame with square steel tubing and I am using a spindle with OpenBuilds c-beam with 8mm lead screw for the Z. Stock motors. Have latest firmware installed. calibration seems to be pretty good.

In approximately 15 operations going from .25" to -.098" it gained about a tenth of an inch depth.

I also put index marks on the shaft, screw and coupler to see if they were slipping. No evidence of slippage.

I do believe this problem has been there since the beginning but have no way to prove it. When cutting my first sled it fell out before the tabs were supposed to be cut. I went back and checked the file but thought I must have made a nube mistake.

[shawn_of_angry_iron] (INSTA Profile

I have some build info on my Instagram.

I am wondering if your z axis pitch setting needs to be tweaked a little.

My first thought would be that coupler is slipping either on the motor shaft, or on the 8mm lead tread.
Other possible reasons:

  • movement on the z-motor plug. From the video it looks like the z-cable is not zip-tied to anything on the sled, so sled moves move the very loose plug of the z-motor.
  • electrical noise induced in the z-axis cable. Separate spindle power cable and z-cable for testing
  • loose encoder
  • broken wire in z-cable
  • i doubt that the c-beam plate is slipping, unless you have run the plate against one end for some time.

With the sled on a table, i would run a g-code with only a bunch of z+/- same distance and watch/film

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Well that seems it would affect both directions. But I have my pitch set to 8.01.

Thanks Gero and Shady. I will for keep trying. I have separated the cables. I will switch the cable with the left motors to see but I am thinking it is in the motor. The way I have the c beam mounted is pretty stout.

EDIT: Post returned, but not applicable to the current thread

I can seem to find it at the moment, but there is a thread that covers a similar problem, and the resulting diagnosis was that the slop in the stock z-axis was to blame. Each downward movement and subsequent upward movement tended to display hysteresis that compounded for each iteration of movement resulting in increasing downward z travel (the first plunge would go .05 inches, but the subsequent retract would only make it .03 inches due to the slop, so the bit would effectively be .02 inches lower than expected). Do this a few times and you get the extra depth you are seeing.

There are techniques that have been developed to mitigate the slop in the stock axis, but I am still an advocate of swapping it out for something like a c-beam axis (or if you have the time, the Meticulous z-axis)

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Separating the cables seemed to do the trick. Posted some video on insta before and after. Now re-running the test. EMI is a MF!

I apparently had not separated them enough before.

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Thanks. No big deal on the withdrawal of your post. I can easily see where that could be an issue! Hence my setup. I did quite a bit of reading on the forum when deciding on the route I wanted to take. The stock router z option seemed very flawed.

Yeah, I did a poor job of reading your previous posts :confused:

No sweat Dude I appreciate the effort. :ok_hand::crossed_fingers::crossed_fingers:

Please put that post back. I can still read it within 24h :wink:
I missed the post you are describing and would like to find it. In any case for any next person who comes here it’s valuable.

I understand, just brainstorming in an attempt to be helpful. A similar thing can happen with the stock z axis as there is a little slop in the lead screw and a little slop in the router body method. With gravity helping on the down motion the down error is magnified. Ahh Keith’s post was gone when I started writing mine. The takeaway I think from both our posts is looking for slop in the mechanics probably wouldn’t be a waste of time. Something is certainly going on, I calculate a ~65% deviation over 15 cycles.

I have added some video on my insta

Great! Looks like you have it handled.