so the extruder arm moves on a track and the bed stays still ?

I guess that's both simpler than moving the bed and potentially more complex to make the crane move exactly parellel to the bed.
Interesting. A bit like a cnc setup.

Okay I'll let you off - that's definitely an interesting project :-)

Um 'selling it' .
You are aware that you will have to build it, stop upgrading it, make it print and then sell it ?
Can you just finish a machine and let it go, without that 'one last tweak' ? ;-)

We'll have to see :-)

I'll do a quick model for what i was thinking about printing a delta frame complete in 2 pieces.
I literally cannot draw things in 2d. My brain just doesn't seem to workj that way.