G28 Problems Mach3

[Propagandalf]

I'm having an issue with G28 at the end of my programs. I'm 2 weeks into G-Code so bear with me. My CAM (fusion 360) spits out

M9
G28 G91 Z0.
G28 X0. Y0.
M30

at the end of the program and it seems to send the XYZ to a random place every time. Sometimes it's fine, other times it exceeds the limitations of one or more of the axes, which of course leads to steppers slipping and losing my X0,Y0 or Z0 for the workpiece. Why isn't this sending it back to the original zero I set in the DRO before running the program? Ideally I'd like it to rapid Z up to a cleared height and return to X0 Y0. This is Mach3, latest version and run through parallel port.

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[daniellyall]

Did you home the machine before useing it.

[Propagandalf]

Did you home the machine before useing it.

I dont have limit switches

[daniellyall]

Theres you problem you home position is somewhere in spaces.

Before you set your work zero move the machine to where you wont it to go at end of job and have the Z axis at near the top of it's travel and hit the ref al home button then Zero to your work pieces, if it does not go back to where you set something else is wrong.

[Fletch_CNC]

I'm not that familiar with Mach, so I'll just throw out a couple suggestions that have worked for me. 1) Is G91 modal in Mach? If not, the second line would switch back to G90, which would cause a different return action than G91 G28. 2) You say you zero the DRO. Is that the same as setting your machine zero? If not, that would explain why you return to a different place each time.

[daniellyall]

What is the Thinking Behind G28?

[mactec54]

I'm having an issue with G28 at the end of my programs. I'm 2 weeks into G-Code so bear with me. My CAM (fusion 360) spits out

M9
G28 G91 Z0.
G28 X0. Y0.
M30

at the end of the program and it seems to send the XYZ to a random place every time. Sometimes it's fine, other times it exceeds the limitations of one or more of the axes, which of course leads to steppers slipping and losing my X0,Y0 or Z0 for the workpiece. Why isn't this sending it back to the original zero I set in the DRO before running the program? Ideally I'd like it to rapid Z up to a cleared height and return to X0 Y0. This is Mach3, latest version and run through parallel port.

Try it like this

M9
G0Z0.
G53X0Y0.
M30

[Propagandalf]

I did figure out how to home the machine without limit switches and it ran all day with out issue always returning to the same place and the XYZ maintaining their accuracy. Thanks for the helps fellas!

[TONYDG]

I did figure out how to home the machine without limit switches and it ran all day with out issue always returning to the same place and the XYZ maintaining their accuracy. Thanks for the helps fellas!

I'm having the same problem, and don't understand the solution of homing the machine without limit switches.

I'm running the program in mach3 without connection to the CNC just for simulation. and after G28 some time it goes to - Z50 other times to Z0 I have set everything to zero before loading the program and once it's loaded.
thank tou
Tony

[dazp1976]

Machine coordinates & work coordinates are 2 seperate things!.

Set up your soft limits in the soft limits page.
I have mine set so they stop 1mm away from the ends of my travel allways round.
Once this is done you can then set a home position for G28.
I only use soft limits atm and have no physical switches but you have to be somewhat alert.

My total travel is Y=185*X=497mm. My soft limits are set as Y= +91.5 & -91.5 (puts Y0.0 in the center, my home). X= +247.5 & -247.5 (puts X0.0 in the center, my home)

My Z travel is around 320mm (can't remember off top of head) but this time my home is near the top.
So soft limits are set as say Z= +70 & Z= -250. This for me puts home at the Z position where it stops with the top of the head ways at the top of the column, not at the full height of travel.

Now when I go G28 it goes to these positions. However if you have a jam and skip steps or skips steps in general then you need to find where your points are again otherwise. 1. You will go beyond table travel, 2. G28 will be out.

Technically you're better off having a home position so the machine co-ordinates know where they are.
You can just edit the G28 commands from Gcode and replace with say a Z move and X&Y 0.0 if it's too much trouble to figure out.

I prefer having a G28 and sending home at the end of day. Then when I switch back on I just click 'ref all home' so it goes green.
I only need G28 at days end so I remove it from gcodes and have a seperate 'home' program I load.
I do have to waste 20 mins or so when/if I lose position which is a pain but if you do things right it's not too often.