After completing the Y-axis it’s time to start building the frame. The printer is 44 blocks high (42 cm). Build a sturdy L-frame of 36 blocks high. This determines how high you can print. But do not build too high. The higher the more unstable the frame. Use LEGO technic bricks (or modified bricks) each 5th brick and use plates for getting a rigid frame (second image). Connect both sides at the top of the frame.
At these websites are some examples of a wooden frame and an acrylic frame.
The 8 mm smooth (50 cm) rod can be placed in a 1×1 stud empty space (8 mm is the exact LEGO 1 x 1 block size). The rod is located at the 36th stud from the front. This isn’t the middle of the base because of the extruder dimensions.
The Nema steppers are attached with 2×4 and 2×8 plates having holes. Build 3 plates high and use m3 x 15 mm bolts. At this point the center of the Nema stepper is 1/2 stud off the 8 mm smooth rod (X and Y axis). This is because of the stepper is placed in the middle of a 2 x 2 opening and the smooth rod is on top of a stud. Therefore the motor is moved half a brick (the X axis). This places the threaded rod exactly opposite the smooth rod (third image).
The smooth rods are attached at the top of the frame. The 5 mm threaded rods (50 cm each) are attached to the stepper motors (5th image). They will be tied to the X-axis.