Homing and 3rd party GRBL apps

RTS · February 28, 2022, 11:34pm

I like my machine’s home to be front left. I know the standard answer to this problem is, “you shouldn’t care about machine coordinates, all you need to worry about is work coordinates.” Well, I understand that logic but … I care about machine coordinates and was wondering if there was a solution to this…

I use Easel for some stuff but also like to use CNCJS for running g-code generated by Fusion 360. When I home with CNCJS, it sets the machine x,y to -749,-749. I understand this to be normal because the grbl standard for “home” is back right. I also understand that grbl does not have a g-code command to reset machine coords to 0,0. So, my solution is to “disconnect” from the x-carve (after homing) then “reconnect”. Machine coords now at 0,0 and all is well. Then I typically run a macro that zips the spindle out to 30,30 (machine coords) where I usually have set up my workspace origin. Then tweak to set a perfect origin for my workspace.

If I forget the “disconnect/reconnect” step to zero machine coords before I run the macro, well, you know what happens - the spindle crashes into the back right of the machine.

Is there any way to automate setting the machine coords to 0,0 after a homing cycle, or change some grbl settings on the x-carve to eliminate the “disconnect/reconnect” step??

SethCNC · March 1, 2022, 1:10am

Sure, just change the move to 30,30 to move to -719,-719 … or include the command for relative movement before the 30,30 move. . Eithet of these wpuld suffice…

An even better solution would be to home, jog into rhe desired 30,30 corner jig location and save that (-719,-719) as a g28.1 and then in order to move it to location aftet homing you would just use the command “g28”

NeilFerreri1 · March 1, 2022, 1:43am

Yes.
Enable HOMING_FORCE_SET_ORIGIN in grbl’s config.
Note, parking will no longer work.

github.com

gnea/grbl/blob/bfb67f0c7963fe3ce4aaf8a97f9009ea5a8db36e/grbl/config.h#L129


      
          
          // Enables single axis homing commands. $HX, $HY, and $HZ for X, Y, and Z-axis homing. The full homing 
          // cycle is still invoked by the $H command. This is disabled by default. It's here only to address
          // users that need to switch between a two-axis and three-axis machine. This is actually very rare.
          // If you have a two-axis machine, DON'T USE THIS. Instead, just alter the homing cycle for two-axes.
          // #define HOMING_SINGLE_AXIS_COMMANDS // Default disabled. Uncomment to enable.
          
          // After homing, Grbl will set by default the entire machine space into negative space, as is typical
          // for professional CNC machines, regardless of where the limit switches are located. Uncomment this
          // define to force Grbl to always set the machine origin at the homed location despite switch orientation.
          // #define HOMING_FORCE_SET_ORIGIN // Uncomment to enable.
          
          // Number of blocks Grbl executes upon startup. These blocks are stored in EEPROM, where the size
          // and addresses are defined in settings.h. With the current settings, up to 2 startup blocks may
          // be stored and executed in order. These startup blocks would typically be used to set the g-code
          // parser state depending on user preferences.
          #define N_STARTUP_LINE 2 // Integer (1-2)
          
          // Number of floating decimal points printed by Grbl for certain value types. These settings are
          // determined by realistic and commonly observed values in CNC machines. For example, position
          // values cannot be less than 0.001mm or 0.0001in, because machines can not be physically more

That said, use work coordinates.

RTS · March 1, 2022, 3:35am

Thanks for the replies. I guess I’m the only one who likes to manually position the spindle to a certain location on my x-carve grid using g-code without having to interpolate the relative position to the workspace origin.

I do think the HOMING_SET_ORIGIN will solve my issue. Thanks for pointing that out. So, if I understand this correctly, I’ll need to modify config.h, recompile grbl for an arduino (ATmega328) and use XLoader to flash the X-Controller? What could possibly go wrong?

NeilFerreri1 · March 1, 2022, 4:01am

I use machine coordinates all the time. I’m ok with the negative coordinates.

You got it. No need for XLoader, though. Just compile and flash from the Arduino IDE.

RTS · March 1, 2022, 2:32pm

I’d be crashing the gantry all the time. Maybe if I rotated the wasteboard 180 degrees .

Ahhh, of course. And, I just noticed that Inventables has a grbl branch for the X-Carve on github, so that should give me a good baseline. It took me a while to realize that the X-Controller is basically just an Arduino board running grbl. I thought there was some proprietary hardware/firmware in that black box.

I built a cnc router/planer for planing large live edge boards a while back and recall doing this same thing when I programmed the Arduino Uno that I used for a controller.

Thanks again.