[RebelTaz]

I built a CNC machine based on this book - CNC Book - Build Your Own CNC Machine

The x- and y-axis seem to be working (relatively) fine. My problem is the z-axis. As the axis is moved up and down over several cycles, the router cuts deeper and deeper. For instance, let's say that I set the z-axis to be 0 with the bit JUST touching the test piece. Then, manually, I can enter (in Mach3) g0 z.125, g0 z0, g0 z.125, etc., etc. over and over again. With each up-down cycle, the bit will begin cutting into the test piece with each cycle cutting deeper and deeper.

I have asked for help on the forums for that book with no solutions. I am hoping that someone here might can help.

I have verified that NOTHING is loose, slack or out of alignment - by completely disassembling and reassembling the entire z-axis assembly. I have swapped the z-axis controller with the y-axis controller with no change. I have also swapped the z-axis motor with the y-axis motor, again with no change...

ANY help would be much appreciated! Thanks...

[kevincnc]

Sounds like you're losing steps. If you slow down your accel/decel and/or speed does it happen? Are you running anything on your computer other Mach during moves?

[tinkeringtechie]

Sounds like you're losing steps.

My guess as well. Try spinning the z-axis shaft manually. Does it catch or become difficult to move at any point (in either direction). Is your router particularly heavy?

[Christian Knüll]

Hi,

I also guess losing steps causes the trouble.

Maybe your motors are a bit undersized for the task?

[vtx1029]

I had the same thing happen with a loose coupler.

[jj_cncguy]

Loose coupler between the stepper and Z screw probably.

Are you using the most recent version of Mach? I had a version of Mach that would lose steps on certain cut files. (This version was from 2011). An upgrade to the latest version of Mach got rid of that problem. This problem was the most obvious on rotary cuts however.

[RebelTaz]

I appreciate the replies. Let me try to answer each one in order.

* I have tried slowing the acceleration and velocity settings with no effect.

* Mach3 is the only thing running. This computer is dedicated solely to the CNC.

* No, the router isn't too heavy, but just to be sure, I have even tried this without the router attached at all - still the same issue.

* The motors are 420 oz steppers. I am attaching the datasheet if that helps.

* I can assure you that the coupling is not loose. I have triple checked this.

* Mach3 is NOT the latest version. That is the ONE thing that I haven't tried.

[ropewrench]

I am not familiar with Mach3 to help threr

however

I had a similar problem with turbocnc
My usb mouse would move and I would loose steps
3 times same g code different places on the g code, but only the Z axis
Z axis would come up with some crazy coordinate when I stopped it

Does it happen in the same spot?
Is there anything else running on your computer?
Check connection
Your z axis cable should be the longest, grounding the shield might help
keep the router and vacuum power away

good luck
Kelly

[beluga282]

I had exactly the same problem ...

My Mach3 configuration was wrong.

In the Config menu, go to "Ports and pins". On the first screen, you wil see "Kernel speed". I suggest to set this option to 25000 first. If your problem is gone, you can try the second option and test it.

This setup is related to the computer you're using.


Bye !!

[RebelTaz]

I had exactly the same problem ...

My Mach3 configuration was wrong.

In the Config menu, go to "Ports and pins". On the first screen, you wil see "Kernel speed". I suggest to set this option to 25000 first. If your problem is gone, you can try the second option and test it.

This setup is related to the computer you're using.


Bye !!

The Kernel Speed is currently set at 25000...

[svanommen]

Sounds like the above folks have covered the most common causes. I too had similar problems. In my case I was either moving too fast, too much weight on the Z axis, and once forgot to fully tighten my bit!

But what about not enough power to your steppers?

Are your stepper cables shielded? Could they be getting interference from something?

Good luck with that. Nothing like having a new machine almost working to drive you up the wall. Been there, done that.

[wayneb]

Hi,

I had a similar problem, Z axis would travel up and down in place, but when X or Y axis moved it played out. I found a break in the Z axis wiring where the wiring pivoted between the axis's.

Cheers
Wayne