CNC machining is a subtractive manufacturing process that uses computer-controlled tools to cut precision plastic parts from sheets, rods, or blocks. Unlike injection molding, it requires no molds, making it ideal for prototyping and small-batch production. This article covers common machinable plastics (ABS, POM, Nylon, Acrylic, PC, PEEK, PTFE, HDPE, PP), key machining parameters, operations (milling, turning, drilling, threading), and design guidelines. Plastics allow higher cutting speeds than metals but need sharp tools, positive rake angles, and adequate cooling to prevent melting. Design recommendations include minimum wall thickness of 0.5–1.0 mm, minimum hole diameter of 0.5 mm, and a depth-to-diameter ratio of 4:1. Standard tolerances of ±0.1 mm are typical. Advantages include no tooling cost, high precision, material flexibility, and fast turnaround. Limitations include material waste, possible warping, and higher per-part cost for large volumes.