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G-Code Introduction

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Introduction


Each machine comes with an instruction manual that shows that particular machine’s code for a specific function. G-code stands for “geometric code,” and follows some variation of the alpha numeric pattern:

N## G## X## Y## Z## F## S## T## M##

  • N: Line number
  • G: Motion
  • X: Horizontal position
  • Y: Vertical position
  • Z: Depth
  • F: Feed rate
  • S: Spindle speed
  • T: Tool selection
  • M: Miscellaneous functions
  • I and J: Incremental center of an arc
  • R: Radius of an arc
Alpha numeric codes are used for programming as they are a simple way to: Define motion and function (G##) Declare a position (X## Y## Z##) Set a value (F## and/or S##) Select an item (T##) Switch something on and off (M##), such as coolant, spindles, indexing motion, axes locks, etc. For example, G01 X1 Y1 F20 T01 M03 S500 would generally indicate a linear feed move (G01) to the given XY position at feed rate of 20. It is using Tool 1, and the spindle speed is 500. Miscellaneous functions will vary from machine to machine, so in order to know what the m-code means, the machine’s instruction manual will need to be referenced. Machine Motion Everything a machine can do is based on three basic types of motion: Rapid move: a linear move to an XYZ position as fast as possible Feed move: a linear move to an XYZ position at a defined feed rate Circular move: a circular move at a defined feed rate Every g-code tells the machine which variation of these basic motions to perform, and how to perform it. X and Y are Cartesian coordinates for horizontal and vertical position, and Z represents the depth of the machine. These alpha numerals will follow the motion/function command (G) to declare the position of the machine. Next, F determines the feed rate (for feed moves or circular moves), while S determines the spindle speed. T is used to select a tool. Other alpha numerals used in programming might include I, J, and R, which have to do with arc centers and radii. Miscellaneous Codes The line of a program might also include m-codes, which are generally codes that tell a machine how to perform an action. While not guaranteed to be the same across machines, some common, standard m-codes are: M00: Program stop M01: Optional program stop M02: End of program M03: Spindle on clockwise M04: Spindle on counterclockwise M05: Spindle stop M06: Tool change M08: Flood coolant on M09: Flood coolant off M30: End of program/return to start M41: Spindle low gear range M42: Spindle high gear range Modality Just like a light will stay on until it’s turned off, g-code functions (on controllers that support modality) will remain active until they are deactivated by another code. In other words, only one function can be active at any given time. To deactivate a function, just select a new function. Example of g code For example, say a code begins with a linear rapid move at X1 Y1 (G00 X1 Y1). If the next function is another linear rapid move, it is not necessary to write G00 again. All that is needed on the next line of code is the new position (say, X2 Y2) because the modal condition is the same. Then, to change the function to a linear feed (G01), programming G01 on the following line would deactivate the linear rapid move and activate the linear feed. Once a condition is set, it stays active until it is turned off or another condition overrides it. Canned Cycles Canned cycles are a kind of modal condition that incorporate all the motions to complete a common task into one code. Lathe programmed with g code to drill For example, oftentimes G81 is code for a basic drilling function. In the case of basic drilling, the tool would have to be 1) moved to the starting point of the hole’s location, 2) rapid to the clearance plane, 3) fed to the depth, and 4) rapid out. That would be four lines of code in the program that would have to be repeated for every new drill position! With the canned cycle G81, only the hole locations need to be specified after activation. Canned cycles like G81 significantly reduce the amount of code by incorporating multiple motions into one code. Example of g code Some other common canned cycles exist for peck drilling, counter boring, and tapping. Learn how to get the most out of your CNC machines in this free eBook. DOWNLOAD Modal Code Groups Modal code groups allow there to be multiple codes on a single line, but there can only be one code from each group on a line. This is because codes within a group will override each other. The modal groups for g-codes are: Group 1 (motion): G00, G01, G02, G03, G80, G81, G82, G84, G85, G86, G87, G88, G89 Group 2 (plane selection – XY, YZ, ZX): G17, G18, G19 Group 3 (absolute/incremental mode): G90, G91 Group 5 (feed rate mode): G93, G94 Group 6 (units – inches/millimeters): G20, G21 Group 7 (cutter radius compensation – CRC): G40, G41, G42 Group 8 (tool length offset – TLO): G43, G49 Group 10 (return mode in canned cycles): G98, G99 Group 12 (work coordinate system selection – WCSS): G54, G55, G56, G57, G58, G59)
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