Performances of 45 individuals with varying degrees of formal and informal training in machining and programming were compared on tasks designed to tap intellectual changes that may occur with the introduction of computer numerical control (CNC). Participants--30 machinists, 8 machine operators, and 7 engineers--were asked background questions and then presented with a series of paper-and-pencil tasks corresponding to the phases of the machining process. Participants' histories demonstrated many different routes into developing skills at work. Those who began careers by learning on the job were less likely to be involved in programming. Younger workers worked with CNC machines more often. The majority felt that hands-on experience supplemented by class work for certain basic topics was the most efficient way to develop skills in machining. Learning and teaching on the job were commonplace. The experimental tasks revealed distinctions in thinking patterns related to hands-on versus programming experience and to machining versus engineering training. They tapped experiential differences and yielded some evidence of mental restructuring due to learning programming. Participants were convinced of the power of hands-on learning and would not recommend a future work force deprived of traditional practical knowledge. Recommendations for CNC machining training included hands-on experience plus class work in basics and up-to-date techniques and continued training and mentoring among employees. (Contains 25 references.) (YLB)