Plan for constructing a special, coffin-shaped bed-of-nails (which I built myself for a sideshow performer friend and client). Maintaining the dimensions while making sure there were exactly 444 nails was tough!

Plans for a wheel calendar (showing the Darian calendar for Mars) to be made from cardboard. A prototype was constructed. 

Above, a diagram of a mathematical function (left), and an unlabeled signal path diagram for some audio equipment (right). Below, a template of LCD segments for generating numbers in a display (not my design, just my handiwork diagramming it).