Before the advent of control technologies such as numerical control (NC and CNC) and programmable logic control (PLC), duplicate parts being milled on a milling machine could not have their contours mapped out by moving the milling cutter in a "connect-the-dots" ("by-the-numbers") fashion. The only ways to control the movement of the cutting tool were to dial the positions by hand using dexterous skill (with natural limits on a human's accuracy and precision) or to trace a cam, template, or model in some way, and have the cutter mimic the movement of the tracing stylus. If the milling head was mounted on a pantograph, a duplicate part could be cut (and at various scales of magnification besides 1:1) simply by tracing a template. (The template itself was usually made by a tool and die maker using toolroom methods, including milling via dialing followed by hand sculpting with files and/or die grinder points.) This was essentially the same concept as reproducing documents with a pen-equipped pantograph, but applied to the machining of hard materials such as metal, wood, or plastic. Pantograph routing, which is conceptually identical to pantograph milling, also exists (as does CNC routing). The Blanchard lathe, a copying lathe developed by Thomas Blanchard, used the same essential concept.
Before the advent of control technologies such as numerical control (NC and CNC) and programmable logic control (PLC) duplicate parts being milled on a milling machine could not have their contours mapped out by moving the milling cutter in a "connect-the-dots" ("by-the-numbers") fashion The only ways to control the movement of the cutting tool were to dial the positions by hand using dexterous skill (with natural limits on a human's accuracy and precision) or to trace a cam template or model in some way and have the cutter mimic the movement of the tracing stylus If the milling head was mounted on a pantograph a duplicate part could be cut (and at various scales of magnification besides 11) simply by tracing a template (The template itself was usually made by a tool and die maker using toolroom methods including milling via dialing followed by hand sculpting with files and/or die grinder points) This was essentially the same concept as reproducing documents with a pen-equipped pantograph but applied to the machining of hard materials such as metal wood or plastic Pantograph routing which is conceptually identical to pantograph milling also exists (as does CNC routing) The Blanchard lathe a copying lathe developed by Thomas Blanchard used the same essential concept