Just found this guy on YouTube who made the simplest homemade CNC build I’ve ever seen. He uses a granite slab as the base and a thick steel piece bent to 90 degrees as the Z-axis. In another video he talks about the play in the machine, I linked the rigidity test and showcase videos below.
For what it is, the thing seems surprisingly stable, even with some 3D-printed parts. i assume the build costs a bit under $1000, which looks like a way better deal than most off the shelf machines you can get at that price. Definitely got me interested in trying something like this once I can budget for it.
Let me know what you think!
Link to project:
Link to Rigidity test: