Yes I know original version of GRBL will not support and there are many issues with UNO board. I'm starting to make bigger is better tabletop cnc machine ASAP and it would be really handy to have 4th axis. Some goooooggling later I found something that might actually work.
https://www.rcgroups.com/forums/show...plete-Solution
https://github.com/fra589/grbl-Mega-5X
https://github.com/LETARTARE/grblQ-Mega-4axes
https://github.com/gnea/grbl-Mega/pull/21
Clearly something is going on, but can't really find any experiences of these and information what goes where is somewhat limited. So anyone over here have any experience on extra axis? Seems like it might work.