Over the last 2-3 weeks I spent a few hours here and there on validating the assembly sequence for mini CNC (http://www.contraptor.org/mini-cnc#assembly) and looking for spots in the alignment process that could use more documentation. One of such spots is the leadscrew alignment - I found that following a few simple rules and knowing how things might go wrong can really shorten the time it takes to get the leadscrew drive working. I will need to write it up in detail but here is the draft: http://www.contraptor.org/leadscrew-alignment
When I started Z-axis assembly, it became clear that the design wouldn't allow to easily perform the leadscrew alignment steps, so I ended up modifying Z-axis to accommodate that. By the way, one of the advantages of construction sets is that a new version of an assembled device doesn't require time/expense of making/buying modified parts, as the case may be with a traditional kit. I simply rearranged the existing parts - construction set is more like software in that sense.
Here is the new Z-axis:
The design allows to assemble and align each of the rails independently.
It also provides more Z axis travel - almost 3" (measured without Dremel). This may be useful for some of the attachments such as drill chuck.
The first tests went well, but when I replaced 6" flat plexi bracket on the rear of X stage with AL angle to enable grounding of the limit switches, I ran into um.. a runtime error when the X stage rear angle crashed into one of the stepper driver heatsinks with Z raised all the way up. I didn't really crash, X stage just kept going, getting more and more skewed as the top was blocked and the bottom continued to move.
So now I have to remove the entire X axis and (mostly) re-assemble and re-align it from scratch. However this means I can take care of another narrow assembly spot - securing X axis to Z stage. It's somewhat difficult with the wrench and using hex socket is almost impossible. There is no reason why the flat screw/nut at the end of the linear rail can't be removed/moved 1" inward - that way it won't interfere with the hex socket.