CNC Programming, G-Code, and CAM
Program structure and motion
Programs move between modal states (G90 absolute / G91 incremental, G20 inch / G21 metric, G17/G18/G19 plane selection) and one-shot commands. Know G00 rapid, G01 linear feed, G02/G03 circular interpolation with center offsets (I, J, K) or radius (R), and the convention that IJK are usually incremental from the start point to the arc center on most controls. Tool length compensation uses G43 with an H register; cutter compensation uses G41 (tool left of path) and G42 (tool right). G54–G59 select work offsets; G53 is machine coordinate; G28 returns to reference through an intermediate point. Canned cycles (G81 drilling, G82 spot drill, G83 peck, G84 tapping, G85 boring) use an R plane and a Z depth; G80 cancels.
CAM and verification
CAM generates toolpaths from a model and a postprocessor converts them to a specific control's dialect. Understand clearance planes, retract heights, lead-in/lead-out, rest machining, and the fact that posted code must be verified - simulation, single block, distance-to-go, and a dry run above the part.
Traps
G41 versus G42 direction, cutter comp activated on an arc or with a lead-in shorter than the tool radius, tapping feed computed wrong, and incremental moves inside canned cycles. Use F = RPM × pitch for G84 (1/4-20 at 500 RPM → F 25.0 in/min).