Here is a parametric 3D CAD program I came across. I have been playing with it for a couple of days and really like it. The program is based on Alibre and geared towards 3D printing. The program sells for $49.00 but you can download a 60 day free trial. Cubify Program: http://www.cubify.com/products/cubify_invent/index.aspx?tb_create_invent Tutorials: http://www.youtube.com/results?search_query=cubify+invent&page=1 Introduction to parametric 3D modeling: https://www.alibre.com/demos/parametrics/parametrics.asp 3D part modeling: https://www.alibre.com/demos/partmodeling/partmodeling.asp Sam