I think, last I read, current board doesn’t have the ability to do 4th axis. Or it could, you’d just have to remove one of the Ystepper motors.
@RichCournoyer did a 4th axis a bit ago, I believe. Let me see if I can dig up the thread on that.
Edit:
Ah, maybe he didn’t post about it here. I did find some stuff on instagram from him:
https://www.instagram.com/p/CFakq3vD4L2/?utm_source=ig_web_copy_link
Edit 2: Here’s a thread about results from reddit: Reddit - Dive into anything
In that thread
I installed a new 5-Axis GRBL board (computer). At present I’m only using 4. It’s called SuperGerbil. It was a Kickstarter project.
Edit 3: If you’re looking to do multi sided machining, an easier way might be to make a jig. Something similar to this: Community challenge #15: Workshop accessory (closed) - #8 by jwhendy
Or Like in @Vince.Fab post here: Community challenge #11: multi-sided machining (closed) - #2 by Vince.Fab