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G20 AND G21 - LENGTH UNITS

Table Of Contents:
  1. G-code Table
  2. G00 - Rapid Linear Motion
  3. G01 - Linear Motion at Feed Rate
  4. G02 and G03 - Arc at Feed Rate
  5. G04 - Dwell
  6. G10 - Coordinate System Data Tool and Work Offset Tables
  7. G17, G18 and G19 - Plane Selection
  8. G20 and G21 - Length Units
  9. G28 and G30 - Return to Home
  10. G28.1 - Reference Axes
  11. G40, G41 and G42 - Cutter Radius Compensation
  12. G43, G44 and G49 - Tool Length Offsets
  13. G47 - Engrave Sequential Serial Number
  14. G53 - Move in Absolute Coordinates
  15. G54 to G59 and G59 P~ - Select Work Offset Coordinate System
  16. G61 and G64 - Set Path Control Mode
  17. G73 - Canned Cycle - High Speed Peck Drill
  18. G80 - Cancel Modal Motion
  19. G81 to G89 - Canned Cycles
  20. G90 and G91 - Distance Mode
  21. G92, G92.1, G92.2 and G92.3 - G92 Offsets
  22. G93, G94 and G95 - Set Path Control Mode
  23. G98 and G99 - Canned Cycle Return Level 
Details:
Program G20 to use inches for length units and program G21 to use millimeters. It is usually a good idea to program either G20 or G21 near the beginning of a program before any motion occurs and not to use either one anywhere else in the program. It is the responsibility of the user to be sure all numbers are appropriate for use with the current length units.
* G20 Example
(Sample Program G20EX9:)
(Workpiece Size: X4, Y2, Z1)
(Tool: Tool #2, 1/4" Slot Drill)
(Tool Start Position: X0, Y0, Z1)

N2 G90 G80 G40 G54 G20 G17 G50 G94 G64 (safety block)
N5 G90 G20 (Set inch mode)
N10 M06 T2 G43 H2
N15 M03 S1000
N20 G00 X1 Y1
N25 Z1
N30 G01 Z-0.125 F5
N35 X3.625 F15
N40 Y1.75
N45 G00 Z1
N50 X0 Y0
N55 M05
N60 M30


* G21 Example
(Sample Program G21EX10:)
(Workpiece Size: X100, Y75, Z25)
(Tool: Tool #2, 8mm Slot Drill)
(Tool Start Position: X0, Y0, Z25.4)

N2 G90 G80 G40 G54 G20 G17 G50 G94 G64 (safety block)
N5 G90 G21 (Set metric programming mode)
N10 M06 T2 G43 H2
N15 M03 S1200
N20 G00 X-5 Y5
N22 Z3
N25 G01 Z-8 F30
N35 G01 X90 F300
N40 X95 Y20
N45 Y50
N50 G03 X75 Y65 R15
N55 G01 X40 Y50
N60 G02 X0 Y10 R40
N65 G00 Z25.4
N70 Y0
N75 M05
N80 M30

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