I'd love a water jet cutter, but they're non-trivial to build. The pump is the main issue, to make 30000+ psi, which is about the minimum needed to cut useful thicknesses of metal at a sensible speed, is both very complex and takes a remarkably large amount of energy. Some commercial ones using 60000 psi consume more than fifty horsepower!

A plasma cutter would be much easier, and in fact a friend is interested in me building a CNC plasma table for him based on my laser cutter design all embiggened, like.

The small cutter will, when redundant, go to another friend, who's looking forward to rehoming it.

pca