This paper presents a provably correct and efficient, polynomial time, planning tool and its application to a miniature assembly line for toy cars. Although somewhat limited, this process has many similarities with real industrial processes. One of our previous polynomial-time planning algorithms has been extended and adapted to work for a larger class of planning problems, including this particular process. The plans produced by the planner are then translated into GRAFCET charts, which are compiled into code for a programmable logic controller. Although capable of producing ordinary assembly plans, the system is mainly intended for producing plans in error recovery situations.