The chance that an abstract CAD model of a plastic part assembly will be perfect the first time is virtually zero. 

WinTech Design recommends that a Stereo Lithography Apparatus (SLA) prototype be made of all new plastic designs. SLA's can then be assembled and checked for form, fit and function before ordering plastic injection molds. 

WinTech coordinates directly with the SLA vendor (such as Solid Concepts, Inc., https://www.solidconcepts.com ). SLA models typically cost from $80 to $500 depending on size and can be made in high resolution or high strength materials.