Hi Mark - The Venn diagram consists of Budget - Application - manufacturing resources - machine foot print (or space available) Often these are contradictory requirements. The answer to the plastic parts is: don't use plastic. Plastic has a modulus of 2-3GPa plywood is 22GPa aluminium is 70GPa steel is 200GPa. Material stiffness and machine rigidity is the grail to chase. Plastic can't supply much stiffness compared to other materials. Peter