CAD/CAM and CNC fundamentals
CAD/CAM and CNC fundamentals tests the path from a drawing or model to a controlled machine tool: coordinate systems, G and M codes, tool offsets, interpolation and safe program structure.
Core rules
- CAD creates geometry and assemblies; CAM converts geometry into toolpaths, then a postprocessor writes machine-specific code.
- CNC axes are named X, Y, Z and rotations A, B, C. Absolute programming with G90 uses coordinates from a fixed origin; incremental with G91 uses distances from the current point.
- G00 is rapid positioning, G01 linear interpolation, G02 and G03 circular interpolation. M codes control machine functions such as spindle and coolant.
- Work offsets locate the part; tool length and radius compensation correct for the actual cutter. Simulation and dry run catch collisions before cutting.
- Feed rate is in mm per minute for milling; spindle speed depends on cutting speed and cutter diameter.
Worked example
From a safe start point, the block G90 G00 X20 Y10 moves rapidly in absolute coordinates to X20, Y10. Then G01 Z-5 F100 feeds vertically to Z-5 at 100 mm per minute. If the program were G91, the same X20 Y10 would mean 20 mm and 10 mm from the current position, not from the datum. The difference matters before the first cut.
Traps
Mixing G90 and G91, forgetting a safe Z clearance, using the wrong tool offset, ignoring cutter radius compensation, and running an unverified program are common causes of scrap and collisions. Units must match the machine setting.