G-code

N40 G01 X50.0 Z-20.0 F0.2 reads as: block 40, feed in a straight line to X50 Z−20 at 0.2 mm per revolution. N numbers the block, G sets the motion, X/Y/Z give the target, and F, S and T set feed, spindle speed and tool.

• G00

  Function

  Rapid positioning — move fast, not cutting

• G01

  Function

  Linear interpolation — straight-line feed (cutting)

• G02 / G03

  Function

  Circular interpolation — clockwise / counter-clockwise arc

• G17 / G18 / G19

  Function

  Select the XY / XZ / YZ plane for arcs

• G20 / G21

  Function

  Inch / millimetre units

• G28

  Function

  Return to machine reference position

• G40 / G41 / G42

  Function

  Cutter compensation off / left / right

• G54

  Function

  First work offset (G55–G59 for others)

• G90 / G91

  Function

  Absolute / incremental positioning

Lathes and mills share most of these but differ on some, and each control maker adds its own codes.

Most G-codes are modal — they stay in force until replaced — so at any moment a control has a set of active codes: the motion mode, plane, units, work offset and compensation. On controls that expose it, ThingConnect reads that active set along with the running program’s name, so it is clear which program a machine is on and in what mode. Program end and pause are handled by M-codes.

Modal state is also why proving out a program matters. If a block assumes G90 absolute positioning but an earlier block left the control in G91 incremental, every following move lands somewhere else. Starting each program, and each tool, with a safe line that restates the key modes — units, plane, positioning, compensation off — removes that risk.