For a history of some of the earliest CAD/CAM and plotters, ref. "A Possible First Use of CAM/CAD" by Norman Sanders, Chapter 4. https://inria.hal.science/hal-

For a history of some of the earliest CAD/CAM and plotters, ref. "A Possible First Use of CAM/CAD" by Norman Sanders, Chapter 4. https://inria.hal.science/hal-01526813/document https://inria.hal.science/hal-01526813/document The gist of the paper is that computer aided manufacturing was developed FIRST, and computer aided design was an offshoot of that. When they had developed their prototype CAD system, the available pen plotters could not output drawings in a high enough resolution to be used for downstream manufacturing processes. "In short, at that time computers could master-mind the cutting of metal with great accuracy using three-dimensional milling machines. Ironically, however, they could not draw lines on paper accurately enough for design purposes; they could do the tough job but not the easy one. However, one day there came a blinding light from heaven. If you can cut in three dimensions, you can certainly scratch in two. Don’t do it on paper; do it on aluminium. It had the simplicity of the paper clip! Why hadn’t we thought of that before? We simply replaced the cutter head of the milling machine with a tiny diamond scribe (a sort of diamond pen) and drew lines on sheets of aluminium. Hey presto! The computer had drawn the world’s first accurate lines. This was done in 1961."