Z axis loses zero

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21 Feb 2020 11:25 #158116 by BobsGotCnc
Z axis loses zero was created by BobsGotCnc
I have been using Linux CNC for about 2 months now and have been have reoccurring issues with the Z axis seeming to lose it's zero. Below I have outlined my procedure and what I am observing. This happens nearly every-time I run the cnc (Joe's Hybrid, HobbyCNC controller).

Procedure to Reproduce Issue:
1) Load gcode.
2) Position the cutter head to where axis zeros should be.
3) Use Touch Off to zero X, Y, and Z axis. Z axis Touched Off the top of the material to align with the Z origin in the gcode.
4) Preview/DRO read the axis are at 0.
5) Run program with a partial material depth cut. Say .125" in .75" thick material.
6) LinuxCNC positions the tool, and then proceed to send the cutter well beyond the gcode commanded location (assuming Z axis zero is where I defined it).
7) Touch Off the Z axis again (to the top of the material). Typically I can visually see the tool path move in the Preview window when I do this....even though I am reseting 0 to the exact same location I did back on step 3.
8) Run the program again.
9) Now everything works correctly.

I am at a loss of what I could be doing wrong or what could be going wrong.

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21 Feb 2020 11:37 - 21 Feb 2020 11:38 #158118 by rodw
Replied by rodw on topic Z axis loses zero
The most likely cause is missing steps on your Z axis. Thais can happen from
1. Velocity too high in the ini file
2. Acceleration too high in the ini file
3. Axis binding
4. stepper voltage too low
5. Current setting mismatched on your stepper controller
Last edit: 21 Feb 2020 11:38 by rodw.

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21 Feb 2020 11:58 #158123 by tommylight
Replied by tommylight on topic Z axis loses zero

The most likely cause is missing steps on your Z axis. Thais can happen from
1. Velocity too high in the ini file
2. Acceleration too high in the ini file
3. Axis binding
4. stepper voltage too low
5. Current setting mismatched on your stepper controller

6. Step time and step space to short.
The following user(s) said Thank You: rodw

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21 Feb 2020 14:56 #158136 by bbsr_5a
Replied by bbsr_5a on topic Z axis loses zero
7. Cable issue controller-driver driver-stepper
8. EM in system at /PlasmaArcStart or VFD run

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21 Feb 2020 15:50 #158139 by MaHa
Replied by MaHa on topic Z axis loses zero
Sometimes G43 is active after toolchange, and maybe your routine uses G49, cancel tollength, so at 2nd try it works correct.

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22 Feb 2020 13:00 #158202 by BobsGotCnc
Replied by BobsGotCnc on topic Z axis loses zero
Incredibly helpful thank you.

Off the cuff the toolchange G43/G49 sounded likely based on what I am seeing.

After playing with it i bit, I now believe I am missing steps. As I ran an engraving program I observed that Z 0 became closer and closer to the table (I zero on the top of the material).

Clarification: Missing steps could be observed through my lead screw not turning while the stepper makes a sort of grinding/pushing noise correct?

Sometime when jogging my Z axis goes up it makes that grinding/pushing noise while the lead screw does not move. It does not do this going down. I can eliminate this behaviour when going up by apply a very minimal pressure up on the spindle with my hand (maybe 2 pounds of force)

Note: When this issue happens during jogging, I have always re zeroed the Z axis. In the past week the amount this has happened has picked up a bit seemingly out of nowhere.

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22 Feb 2020 15:47 #158214 by NewToRouting
Replied by NewToRouting on topic Z axis loses zero
Did you ever resolve this issue? I'm having the same problem. I touch X,Y,Z Axis . The bit hovers over the material but never cuts anything. The X and Y runs through fine. I've cut things in the past with the machine configured the same way but had to reinstall.

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22 Feb 2020 15:48 #158215 by persei8
Replied by persei8 on topic Z axis loses zero
From your description, it sounds like a slipping coupler or the motor not having enough torque to lift the weight of the Z axis. Also double check the setup and hold times in the ini file.

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22 Feb 2020 16:13 #158218 by bbsr_5a
Replied by bbsr_5a on topic Z axis loses zero
sometimes people also use ESTLCAM with this tiny Zbounces at 0,02mm that breaks of the Zprecision
Take that to Zero in your CAM if you got this Zfreemovement present

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24 Feb 2020 23:34 #158428 by BobsGotCnc
Replied by BobsGotCnc on topic Z axis loses zero
Not completely solved but getting closer.

1st win, adjusting the eccentric bearings to ensure the Z carriage was going up with as little resistance as possible. Had to add two washers to push the bottom bearings out further from the carriage that the top two bearings.


Still having zeroing issues, but likely is related to the tool change that seems to always be mentioned the first time I run G-Code (from Fusion 360, using the LinuxCNC output option). I need to dig into this more.

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