
8.COORDINATE VALUE AND DIMENSION PROGRAMMING B-63944EN/02
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8.2 INCH/METRIC CONVERSION (G20, G21)
Either inch or metric input (least input increment) can be selected by
G code.
Format
G20 ; Inch input
G21 ; Metric input
This G code must be specified in an independent block before setting
the coordinate system at the beginning of the program. After the G
code for inch/metric conversion is specified, the unit of input data is
switched to the least inch or metric input increment of increment
system (II-2.3). The unit of data input for degrees remains unchanged.
The unit systems for the following values are changed after
inch/metric conversion:
• Feedrate commanded by F code
• Positional command
• Workpiece origin offset value
• Tool compensation value
• Unit of scale for manual pulse generator
• Movement distance in incremental feed
• Some parameters
When the power is turned on, the G code is the same as that held
before the power was turned off.
WARNING
G20 and G21 must not be switched during a
program.
NOTE
1 When the least input increment and the least
command increment systems are different, the
maximum error is half of the least command
increment. This error is not accumulated.
2 The inch and metric input can also be switched
using settings (see III-12.3.1).