Glossary & Reference
A CNC machine turns a written program into precise, repeatable motion — swapping the machinist's handwheels for a computer that drives every axis to the exact same position, cut after cut, part after part.
CNC stands for Computer Numerical Control. Instead of an operator manually cranking handwheels to position a cutter, the machine's motion is driven by a controller executing a stored program — commonly written in G-code — that tells each axis exactly where to go, how fast to get there, and what the spindle should be doing along the way. The controller handles the moment-to-moment math; the operator sets up the job, loads the program, and supervises the run.
Every CNC axis — X, Y, Z, and any rotary axes — has its own servo motor and drive. The controller sends a position command to the drive, the drive energizes the motor, and the axis moves. A feedback device, usually a rotary encoder mounted on the motor or the axis itself, reports the actual position back to the controller many times per second. The controller compares commanded position against actual position and continuously corrects any difference. That constant compare-and-correct cycle is what makes it a closed-loop system, and it's the reason a CNC machine can hold tight tolerances cut after cut without someone watching every move.
CNC grew out of numerical control, or NC, developed in the mid-20th century, where machine motion was driven by instructions punched onto paper tape and read one block at a time with no onboard computer to store or edit a program. As computers became small and affordable enough to build directly into the machine control, NC evolved into CNC — programs could be stored, edited, and re-run instantly, and far more complex motion became practical. Modern shop controllers are the direct descendants of that shift.
Because motion is programmed and feedback-corrected rather than hand-guided, a CNC machine repeats a cut the same way on part one and part one thousand — critical for interchangeable parts and tight tolerances. It can also execute geometry that would be impractical to cut by hand, run unattended through a lights-out shift, and deliver a level of part-to-part consistency that a manual process depends entirely on operator skill and fatigue to match.