Newbie Z axis woes

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13 Apr 2023 12:20 #268969 by rthorntn
Newbie Z axis woes was created by rthorntn
Hi,

Please be gentle.

I have a 6040 CNC, the three axis steppers are all wired into the G540 the same.

My Z moves up when it should move down, I inverted it in the ini and it moves in the correct direction.

My Z home switch is at the top of travel, farthest from the table.

I setup combined home and limits (is this a bad idea?) on all axis (3 mechanical switches (XYZ, all switches at the end of an axis, wired to separate pins), it backs off 2mm (actually -2mm on Z because of the inversion).

I'm thinking I should swap the Z stepper wires instead.  Why you ask, well with the software inversion other people's g-code doesn't work...

I'm pretty sure this is because the software inversion means you are using minus (-) values in the ini because everything is in reverse and swapping the wires would mean I could just use positive values?

This bit makes my head hurt, with Z on a CNC like mine, machine zero is at the top of the travel right, furthest from the table, now as you move the Z axis down towards the table, say 25.4mm, what should your LCNC DRO read "25.4mm" or "-25.4mm"?

I got a bit of g-code from someone and one of the final moves was to send the Z  to 10 (G90 G00 G53 Z10) and that gives me an error.

Thanks 
Richard

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13 Apr 2023 17:52 #268983 by JPL
Replied by JPL on topic Newbie Z axis woes
As you can see here: linuxcnc.org/docs/stable/html/user/user-...chine-Configurations

With Z=0 at the top, moving down should increase the NEGATIVE value of the position. The DRO should then say -25.4 for your example.
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13 Apr 2023 18:16 #268984 by JPL
Replied by JPL on topic Newbie Z axis woes

...
I got a bit of g-code from someone and one of the final moves was to send the Z  to 10 (G90 G00 G53 Z10) and that gives me an error.
...

 


Be careful with G53 move as those are in 'machine coordinates' and often related to the specific design of the machine. Have a look here for more info: linuxcnc.org/docs/stable/html/user/user-...#_coordinate_systems

In this case I would think that this program was intended for a machine having the home position near the table, not at the top where it usually is (and recommended).
 
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13 Apr 2023 18:20 #268985 by tommylight
Replied by tommylight on topic Newbie Z axis woes
First, take a break.
Then, Z axis 0 or max should be at the top, as JPL noted above, and shold go negative towards the table.
There is a procedure for touching off at the top of material before starting work and setting the top of meterial as G54 Z0.
Probably should read about it as i am not good at explaining.
If using Axis GUI, then jog the Z with the tool on to the top of meterial, click on "touch off" near the "home all" button, that will set Z0.
After this even if you have Z10 in gcode it should work, as long as there is no G53 Z10 there.
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15 Apr 2023 03:30 #269053 by rodw
Replied by rodw on topic Newbie Z axis woes
First off, there is nothing wrong with shared home/limit switches. You just need to be sure to use a home_offset to move off the home switch otherwise you will trigger a limit switch error after it comes out of homing.

The biggest revelation I had as a newb was to use the G54 offsets to set the zero position and forget about G53
linuxcnc.org/docs/2.9/html/gcode/g-code.html#gcode:g54-g59.3
The best way to do this for Z is to use a milling cutter or drill bit of known diameter (lets assume its 10mm) jog down until you can just roll the drill bit under your tool. Then use the touch off feature to touch off at 10mm. This is equivalent to running G54 Z10 in the MDI window. Watch The DRO's to confirm the zero position has changed. Now Z0 will be the top of your job.

Likewise use a wobbler to touch off your X0 & Y0 coordinates. Say your wobbler is 6mm in diameter (3mm radius) and you are touching off at top left,
touch off x = 3mm, y=3mm. Alternatively, a sharp pointer in the spindle should let you position to X0,Y0 so touch off accordingly.

This is no  different how I would use a DRO on a manual mill.



 
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