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Author Topic: Can I use the g28 Code to set a "Forever Home Position" in Mach 3  (Read 1094 times)

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Hi Still Learning....Can I set a permanent home position via the g28 code....so when I shut down....x y and z will know where "home is"
in Mach 3 when I start up the next day
Re: Can I use the g28 Code to set a "Forever Home Position" in Mach 3
« Reply #1 on: October 10, 2017, 01:45:47 PM »
Hi,
not really. If you drive to some known location, 'home' for instance and then shut down. When you next fire Mach up you could
'home in place' which assigns 0,0,0 to the current location. That requires that every time you shut down that you go to the same
location and second that as you power on the machine doesn't move and my experience is that it does as the drivers power up
and the motors 'lock up'

What you are trying to do here is avoid putting quality home switches in your machine and setting up index homing if your servos/steppers are
capable of it. Don't be a plonker, put home switches in and be done with it...repeatable, accurate, easy for multiple operators.

Craig
My wife left with my best friend...
     and I miss him!
Re: Can I use the g28 Code to set a "Forever Home Position" in Mach 3
« Reply #2 on: October 10, 2017, 01:49:27 PM »
I was looking at that as well...Popped open the controller box to see what I was in for.....If I Home at the end of the day and shut down...All is well.....I should say If I remember to home at the end of the day all is well :)
Re: Can I use the g28 Code to set a "Forever Home Position" in Mach 3
« Reply #3 on: October 10, 2017, 02:16:25 PM »
Hi,
if you have home switches it doesn't matter where you shut down so long as you reference your machine at start up it will always be in the right
place.

I can shut Mach down, come back the next day, fire up and reference and re-start the PCB job still in the vice from yesterday. The referencing I've
found to be as good as 0.02mm and that's just with microswitches and would be better again with index homing. So easy....I like you tried all sorts
of ways to get around this...and wasted my time doing all of them UNTIL I put in good home switches.

Craig
My wife left with my best friend...
     and I miss him!
Re: Can I use the g28 Code to set a "Forever Home Position" in Mach 3
« Reply #4 on: October 11, 2017, 02:21:32 AM »
Hi,
at one stage of the piece I was having some bother crashing Mach4 and I found it necessary to reset the machine several times in one session.
I can't recall what I was doing wrong but any way I was restarting, homing and then running the same Gcode that I'd been running
prior to  crashing Mach. I had done this three or four times before I made a mistake, I reset the machine and started the Gcode running BEFORE
I'd referenced the machine. Of course disaster struck and I drove the spindle into the workpiece.

As a result of this I've coded my machine to ignore any jogging, MDIing or <cycle start> until I reference the machine. I do have a button to override
this behaviour if I wish or need but it means I can't accidentally due to brain fade do anything UNTIL the vital referencing after a reset or start.

I know a few experienced CNCers don't bother with home switches. I did operate like that for a while but found that it was very easy for me to
confuse zeroing my work co-ords and zeroing my machine co-ords. Also I found that because of that confusion soft limits not to be useful, they only
work well when the machine co-ords are referenced to a known and repeatable place.

The quality and repeatability of my work has gone up a great deal and the number of mistakes reduced a great deal since I fitted good home switches.

Craig
My wife left with my best friend...
     and I miss him!