I've making good progress in constructing my MK2 varient and I need to set the correct P.I.N.D.A. probe height.
There is an interesting open source router called a TopsCnc that can mostly be made using 3d printed plastic parts and also aluminium extrusion.
I'm not really sure I have a purpose for such a machine, but it is curious.
A bit beefier is the PrintNC. Looks pretty simple to put together.