These sketches helped me wok out which axes I wanted to have, how they would move, and what things would generally look like. I decided to use a combination of aluminum and acrylic to make the mill. Machining some parts out of aluminum was both necessary and poetic, since I needed good precision and making parts for my model mill with a real mill amused me. Acrylic could be see-through, which would let people see how the mechanism worked and also allowed for rapid prototyping and adjustments if a design didn't work the first time. My sketch also helped with scale, since when I had a rough sketch of the size I could start putting actual dimensions to the parts. Once I had the ideas down on paper, I could start CADing my mill. I knew I had to use CAD, since making the mill move would require pretty high precision. Making the parts by eye wouldn't work in this case. I had to work out that the x axis would move just the acrylic table, the Y axis would move the table and the rod that moved the X axis, and the Z axis would move the table, the X axis rod, and the Y axis rod. I would use regular 10-32 threaded rod instead of ball or lead screws to save money and make more hardware (like standard tapping tools and nuts) available to use. I started with the table that would move in the X and Y directions, since I was most worried about making that motion work and be reasonably faithful to a real Bridgeport. My first CAD assembly is shown below.