Step 1: Download and laserize
What those of you without laser cutters (poor souls that you are) may take away is this cool construction method I learned from puzzle maker Lee Krasnow. I measured my screws, nuts, and washers, and modeled them simply in cad. I measured the width of my plexiglass. Knowing those dimensions, I could make some tabs in the design. When the design is put together, the tabs keep the different panels aligned and square to one another. the screws fit down through the holes, and connect with the nuts in the adjacent panel. The nuts are held fixed by their tight fitting in the plastic. Putting these together is a breeze, really.