A piece of the same aluminum profile used for the linear guides is used here in order to make a trapped nut, that will be used for the drive mechanism with the brass screw rods. I also used ready-made brass nuts here, which were cut in the appropriate length.
And here how the trapped nut is fitted inside the carriage. You may notice that some of the holes I made were not very accurately aligned. This is due to a combination of poor tools and technique. But I used larger holes for the screws, in order to be able to align the parts properly. I also use safety nuts wherever possible, because the CNC is expected to have lots of vibrations and given that the holes for the screws are slightly bigger, there is no room for loose nuts.
Finally, the controller of the CNC. Basically an Arduino Duemilanove with the Motor shield from Adafruit. Unfortunately the Motor Shield supported only 2 step motors, so I used relays and a spare pin from Arduino, in order to “multiplex” the Y-axis and Z-axis.