Cut by Numbers

For decades, many of the most profound human innovations have demanded an inhuman precision. From contours that reduce a car’s drag to the invisibly tiny features on a silicon chip, today’s technological wonders would be impossible to fabricate using eyes and hands alone. Manufacturer John T. Parsons helped boost human production ability as a pioneer in computer-aided manufacturing. By translating machine motions into a set of numbers, Parsons taught machines to build machines.

In 1947, John Parsons headed the Parsons Corporation plant in Traverse City, MI, which produced helicopter rotors. At the time, digital computers were still gymnasium-sized affairs, but punch-card-operated electromechanical calculators were used by accountants. Parsons rented an IBM accounting machine to crunch some design parameters, since the shape of his rotor blades was defined by complicated equations. No one suspected that the machine would ultimately help Parsons produce finished parts with unprecedented accuracy and speed.

To make blade templates, workers had traditionally begun by marking 17 points that defined a template’s curve-each laboriously calculated with a slide rule. They would then manually draw contours to connect the points, make a rough cutout of the shape, and file the piece down to specifications. Even with skilled workers, the process inevitably yielded errors that led to ruined templates and wasted time.

The IBM calculator, however, gave Parsons an idea. He asked employee Frank Stulen to compute 200 points along the edge of the contour, using the calculator. Parsons then had a machinist drill a hole at each of the 200 sets of coordinates. As the holes were now close enough to overlap, there was no need for additional tracing or cutting. All a machinist had to do was move the machining platform to the desired coordinates, drill a hole, move to the next coordinates, and repeat.

The technique still relied on a human to operate the machine, but Parsons envisioned the next step to automation-a motor-driven machine that was fed the numerical instructions via punch cards. Parsons took his idea to the U.S. Air Force, which granted him a contract but eventually gave control of the project to MIT. Nevertheless, today John Parsons is recognized as the father of “numerical control,” and he was awarded the National Medal of Technology in 1985.