Step 1. Held upright the main frame is after the acrylic fender washers on the threaded rods. Here you can use the A2 panel as a reference to measure the distance A1 and A12 (the rear plate).
Step 2. Screw up the main frame to the acrylic fender with M3 x 20 screws.
Step 3. Screw up the M10 screw on the threaded rod of Y-axis. You can see the finished picture.