My main design approach is to build scale models as it allows me to fully conceptualize and visualize the finished piece. I start with sketches to define the overall structure and design elements of the piece. I seldom move to detailed engineering drawings, and I don't use computer automated design (CAD). Using the sketches as a base, I then build 20% scale models. The real design work comes in the models. I can easily make and modify multiple models to test and visualize the design. Once I'm satisfied with the models I build directly from them by scaling up appropriately. Often times I'll make full scale mock-ups of key pieces to verify the design integrity and to work through mechanical issues like joints. When the final piece is done there really are two pieces, the end product and its companion model.