Z axis loses zero

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26 Feb 2020 03:25 #158504 by BobsGotCnc
Replied by BobsGotCnc on topic Z axis loses zero
Once I start the Gcode a tool change dialog comes up (not sure why).
After this dialogue it appears the Z axis is no longer zerod. If I attempt to use Touch Off, it does not put the Z axis to 0 but rather .6nnn . Oddly that .6nnn number it goes to is consistent and repeatable. To be clear, when the Touch Off dialogue appears, I do have 0.0 entered. But it does not actually zero the Z access post tool change dialogue. If I instead use the Tool Touch Off, I can zero the Z axis.

Any ideas what I am doing wrong here?

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26 Feb 2020 04:09 #158505 by Todd Zuercher
Replied by Todd Zuercher on topic Z axis loses zero
It sounds like you have a tool offset saved and your g-code is loading the tool and offset.

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26 Feb 2020 23:38 #158582 by BobsGotCnc
Replied by BobsGotCnc on topic Z axis loses zero
Would the offset be in the GCode or in LinuxCNC?

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27 Feb 2020 00:34 #158589 by Leon82
Replied by Leon82 on topic Z axis loses zero
If you type in g49 in mdi what happens to the position readout?

It sounds like after the tool change completes it calls out g43 tool height offset

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03 Mar 2020 03:29 - 03 Mar 2020 03:29 #159063 by BobsGotCnc
Replied by BobsGotCnc on topic Z axis loses zero
Here is outcome of checking g49 and g43.

1. Zeroed Z axis. DRO read 0. Loaded G-coded.
2. Started file (play button in UI).
3. Tool change dialogue appears. I choose okay (cause I do not need to change the bit...would love to get rid of this tool change)
4. Bit proceeds to dive into the work piece (3/4" wood) a 1/2". It should only be going in about an 1/8" (vcarve operation)
5. While at this too far plunged depth, G43 read 0.1595 (yeah it was well below this depth) and G49 read -0.4567 (more likely where the bit was at).

For step 5, I used MDI and the DRO with the program stopped and without moving the x,y,z axis.

Gcode that had run up to my stopping the program (using the Stop button in the UI):
%
(1001)
(T1 D=0.75 CR=0. TAPER=45DEG - ZMIN=-0.1427 - CHAMFER MILL)
N10 G90 G94 G17 G91.1
N15 G20
N20 G53 G0 Z0.
(ENGRAVE2)
N25 T1 M6
N30 S20000 M3
N35 G54
N40 M8
N45 G0 X1.087 Y-5.076
N50 G43 Z0.5 H1
N55 G0 Z0.2
N60 G1 Z0. F39.37
Last edit: 03 Mar 2020 03:29 by BobsGotCnc. Reason: Spelling.

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05 Mar 2020 14:27 #159260 by andypugh
Replied by andypugh on topic Z axis loses zero
Check your tool table. Are there any offsets in there?
The following user(s) said Thank You: BobsGotCnc

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05 Mar 2020 14:30 #159261 by andypugh
Replied by andypugh on topic Z axis loses zero

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


This sounds like a weak stepper, or driver.

Try increasing the Z axis driver current, if you can. Monitor the motor temperature (but be aware that "uncomfortably hot to touch" is well inside the operating envelope of a stepper motor.

Also try reducing the max acceleration (especially) and the max velocity of the Z axis. You might even be able to _increase_ the velocity if you drop the accelleration.
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09 Mar 2020 02:30 #159552 by BobsGotCnc
Replied by BobsGotCnc on topic Z axis loses zero
The Tool Table was the solution. In there I found the Z offset that keeping getting applied. Cleared it out, and things the two operations I did today went well.

Thank you.

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09 Mar 2020 02:34 #159553 by BobsGotCnc
Replied by BobsGotCnc on topic Z axis loses zero
I agree on the current and driver. I am working on upgrading from MyHobbyCNC driver to StepperOnline DM542T (outputs more current and higher torque) and a larger power source (34v to 48volts with respective current needs).

Thank you.

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