1) Take the build plate support block. Mark the block on either side in the center, 2 cm from the longest edge. Drill the hole with the 11/32-in drill bit. Push the nuts from the thread screws through each hole. It should be a tight friction fit. For added stability, use #8 1/2-in screws to secure the nut.
2) Place the shaft couplers on the two remaining stepper motors and use a hex key to tighten them as appropriate. Place the thread screws in the other end of the shaft couplers and tighten them again. Use Zip ties to secure the stepper motors to the bottom of the milk crate.
3) Place the build plate support on the thread screws and twist the screws to lower the plate. Slide the top plates over the thread rods to make sure everything is in place.