3D Printing: How to Join the Z, X, and Y Axes All Together on the Prusa i3
Once you have the assembled Z/X axes and a separate assembled Y axis, you need to join both parts of the 3D printer frames together, align everything, and tighten. The metal plate of the Z/X axes is fitted together with the set of M10 nuts and washers in the middle section of the Y axis, as detailed below:
Slot the assembled Y axis into the middle of the vertical laser-cut Z/X frame and lower down so the M10 rods sit into the frame cut-outs.
Make sure one M10 nut and washer are on either side of the aluminum frame.
Measure each side of the M10 threaded rods and align the aluminum frame into the middle of the rod.
It is not essential at this point to have an exact middle point, as you will need to adjust this after you fit the extruder. When you are at the home position (0,0,0), the extruder nozzle is sitting in the front-left corner of the build plate. This distance should also be specific to the type of extruder and hot-end you choose to fit.
Tighten you the M10 nuts secure enough so the frame won't fall apart while you wire up the electronics.