The three buttons, from left to right:
- Feed Hold/Pause: this issues a hardware feed hold command (aka pause) to GRBL. By default on the Xcontroller, it will turn off the spindle output, turn off the M7/M8 outputs and raise the spindle to just below the machine zero position. Press the resume button to start again.
- Resume: resumes the current program. It clears the feed hold condition. It will lower the spindle down to safety height or work zero (can’t remember which), turn on the spindle and turn on M7/M8 and then go to the Z depth it was and resume accepting commands from Easel/UGS.
- Abort: this does a soft reset of GRBL. It aborts execution of code, turns everything off, and usually signals to the Gcode sender to stop sending commands.
How to use them? That’ll differ from person to person.
I use pause/feed hold if I need to go upstairs for dinner, use the restroom, or the dog or anything that I want the machine to be in a safe state but not abort the carve. I’ve heard of people leaving it in feed hold overnight for really long carves. Everything stays powered and the next day you just hit resume and it’s carving where you left off. Not saying I recommend that, but it’s possible.
I’ve found abort is most useful if you loaded the wrong program and realized it as the machine runs to the wrong spot. It’s when you want an immediate cancel but don’t want to hit the Estop to turn off power. Abort is a stop for non dangerous situations where the Estop is for “oh crap that’s gonna cause some damage”. Abort allows a Gcode sender to gracefully recover from the stop as well where an Estop requires you to generally force stop it and maybe even restart the program as the com port is lost.