CNC Machining Center Instruction on British / Metric Units: G20 / G21
G20: Set the program in units of “inches”. The minimum value is 0.0001 inches.
G21: Set the program in units of “mm”. The minimum value is 0.001mm.
CNS uses metric units, so the CNC milling machine or MC is automatically set to metric units “mm” as soon as it is turned on. Therefore, there is no need to command G21 in the program. However, if you want to machine a workpiece with “inch” as the unit, G20 must be commanded in the first block of the program. The coordinate value, feed rate, thread lead, tool radius correction value, and tool length correction commanded below The value, unit value of each hand wheel of MPG hand wheel, etc. are all set to imperial units.
G20 or G21 is usually used alone and does not appear in the same block with other instructions, and should be located in the first block of the program.
Only one unit can be used in the same program, and it cannot be mixed in metric and imperial systems.
Tool correction values and other related values must be reset as the unit system changes.