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{{Redirect|G-code|other uses|G-code (disambiguation)|and|G programming language (disambiguation)}} {{short description|Primary programming language used in CNC}}
{{other uses|G-code (disambiguation)|G programming language (disambiguation)}}
{{redirect|RS-274|the photoplotter format|Gerber format}}
{{Infobox programming language {{Infobox programming language
| name = G-code | name = G-code
| file ext = .gcode, .mpt, .mpf, .nc and several others
| logo =
| paradigm = ], ]
| caption =
| released = {{Start date|1963}} (RS-274)
| file ext = .mpt, .mpf .nc and several others
| designer = ]
| paradigm =
| developer = ] (RS-274), ] (ISO-6983)
| released = 1950s (first edition)<!-- {{Start date|YYYY}} -->
| implementations = Numerous; mainly ] Sinumerik, ], ], ], ], ]
| designer = ]
| dialects =
| developer =
| influenced by =
| latest release version =
| influenced =
| latest release date = <!-- {{start date and age|YYYY|MM|DD}} -->
| programming language =
| latest preview version =
| platform =
| latest preview date = <!-- {{start date and age|YYYY|MM|DD}} -->
| operating system =
| typing =
| license =
| implementations = many, mainly ] Sinumeric, ], ], ], ]. Generally there is one international standard - ] 6983.
| website =
| dialects =
| wikibooks =
| influenced by =
| influenced =
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| platform =
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'''G-code''' is the common name for the most widely used ] (CNC) ], which has many ]s. Used mainly in ], it is part of ]. G-code is sometimes called '''G programming language'''. (The names of the language are explained at "]".)


'''G-code''' (also '''RS-274''') is the most widely used ] (CNC) and ] ]. It is used mainly in ] to control automated ]s, as well as for ]. The ''G'' stands for geometry. G-code has many variants.
In fundamental terms, G-code is a language in which people tell computerized ]s what to make and how to make it. The "what" and "how" are mostly defined by instructions on where to move to, how fast to move, and through what path to move.


G-code instructions are provided to a ] (industrial computer) that tells the motors where to move, how fast to move, and what path to follow. The two most common situations are that, within a machine tool such as a ] or ], a ] is moved according to these instructions through a toolpath cutting away material to leave only the finished workpiece and/or an unfinished workpiece is precisely positioned in any of up to nine axes<ref>Karlo Apro (2008). ''''. Industrial Press Inc. {{ISBN|0-8311-3375-9}}.</ref> around the three dimensions relative to a toolpath and, either or both can move relative to each other. The same concept also extends to noncutting tools such as ] or ] tools, ], additive methods such as 3D printing, and measuring instruments.
==Implementations==
The first implementation of numerical control was developed at the MIT Servomechanisms Laboratory in the early 1950s. In the decades since, many implementations have been developed by many (commercial and noncommercial) organizations. G-code has often been used in these implementations. The main standardized version used in the United States was settled by the ] in the early 1960s.{{Citation needed|date=March 2010}} A final revision was approved in February 1980 as ''RS274D''. In the world, the standard ''] 6983'' is often used, although in varied states of Europe sometimes used other standards, example ''] 66025'' or PN-73M-55256, PN-93/M-55251 in Poland.


== History ==
Extensions and variations have been added independently by control manufacturers and machine tool manufacturers, and operators of a specific controller must be aware of differences of each manufacturer's product.


The first implementation of a numerical control programming language was developed at the ] in the 1950s. In the decades that followed, many implementations were developed by numerous organizations, both commercial and noncommercial. Elements of G-code had often been used in these implementations.<ref>{{cite book | last=Xu | first=Xun | date=2009 | url=https://books.google.com/books?id=habcATPQWJ4C | title=Integrating Advanced Computer-aided Design, Manufacturing, and Numerical Control: Principles and Implementations | publisher=Information Science Reference | page=166 | isbn=978-1-59904-716-4 | via=Google Books}}</ref><ref>{{cite book | last=Harik | first=Ramy | author2=Thorsten Wuest | date=2019 | url=https://books.google.com/books?id=O3h0EAAAQBAJ | title=Introduction to Advanced Manufacturing | publisher=SAE International | page=116 | isbn=978-0-7680-9096-3 | via=Google Books}}</ref> The first ] version of G-code used in the United States, ''RS-274'', was published in 1963 by the ] (EIA; then known as Electronic Industries Association).<ref>{{cite book | last=Evans | first=John M. Jr. | date=1976 | url=https://www.govinfo.gov/content/pkg/GOVPUB-C13-2ef4aaa5a150eedcb85a1e6985e90bfa/pdf/GOVPUB-C13-2ef4aaa5a150eedcb85a1e6985e90bfa.pdf | title=National Bureau of Standards Information Report (NBSIR) 76-1094 (R): Standards for Computer Aided Manufacturing | publisher=National Bureau of Standards | page=43}}</ref> In 1974, EIA approved ''RS-274-C'', which merged ''RS-273'' (variable block for positioning and straight cut) and ''RS-274-B'' (variable block for contouring and contouring/positioning). A final revision of ''RS-274'' was approved in 1979, as ''RS-274-D''.<ref>{{cite journal | last=Schenck | first=John P. | date=January 1, 1998 | url=https://link.gale.com/apps/doc/A20429590/GPS?sid=wikipedia | title=Understanding common CNC protocols | journal=Wood & Wood Products | publisher=Vance Publishing | volume=103 | issue=1 | page=43 | via=Gale}}</ref><ref>{{citation| title = EIA Standard RS-274-D Interchangeable Variable Block Data Format for Positioning, Contouring, and Contouring/Positioning Numerically Controlled Machines |publisher = Electronic Industries Association |location= Washington D.C. |date=February 1979}}</ref> In other countries, the standard ''] 6983'' (finalized in 1982) is often used, but many European countries use other standards.<ref>{{cite book | last=Stark | first=J. | author2=V.&nbsp;K. Nguyen | date=2009 | url=https://books.google.com/books?id=RIgLRe12RD4C | chapter=STEP-compliant CNC Systems, Present and Future Directions | title=Advanced Design and Manufacturing Based on STEP | editor-last=Xu | editor-first=Xun | editor2=Andrew Yeh Ching Nee | publisher=Springer London | page=216 | isbn=978-1-84882-739-4 | via=Google Books}}</ref> For example, ''] 66025'' is used in Germany, and PN-73M-55256 and PN-93/M-55251 were formerly used in Poland.
One standardized version of G-code, known as ''BCL'', is used only on very few machines.


During the 1970s through 1990s, many CNC machine tool builders attempted to overcome compatibility difficulties by standardizing on machine tool controllers built by ]. ] was another market dominator in CNC controls, especially in Europe. In the 2010s, controller differences and incompatibility are not as troublesome because machining operations are developed with CAD/CAM applications that can output the appropriate G-code for a specific machine tool. During the 1970s through 1990s, many CNC machine tool builders attempted to overcome compatibility difficulties by standardizing on machine tool controllers built by ]. ] was another market dominator in CNC controls, especially in Europe. In the 2010s, controller differences and incompatibility were mitigated with the widespread adoption of CAD/CAM applications that were capable of outputting machine operations in the appropriate G-code for a specific machine through a software tool called a post-processor (sometimes shortened to just a "post").


== Syntax ==
Some CNC machines use "conversational" programming, which is a ]-like programming mode that either hides G-code or completely bypasses the use of G-code. Some popular examples are Southwestern Industries' ProtoTRAK, Mazak's Mazatrol, Hurco's Ultimax, Haas' Intuitive Programming System (IPS), and Mori Seiki's CAPS conversational software.


G-code began as a limited type of language that lacked constructs such as loops, conditional operators, and programmer-declared variables with ]-word-including names (or the expressions in which to use them). It was thus unable to encode logic; it was essentially just a way to "connect the dots" where many of the dots' locations were figured out longhand by the programmer. The latest implementations of G-code include such constructs, creating a language somewhat closer to a ]. The more a programmer can tell the machine what end result is desired, and leave the intermediate calculations to the machine, the more (s)he uses the machine's computational power to full advantage. G-code began as a limited language that lacked constructs such as loops, conditional operators, and programmer-declared variables with ]-word-including names (or the expressions in which to use them). It was unable to encode logic but was just a way to "connect the dots" where the programmer figured out many of the dots' locations longhand. The latest implementations of G-code include macro language capabilities somewhat closer to a ]. Additionally, all primary manufacturers (e.g., Fanuc, Siemens, ]) provide access to ] (PLC) data, such as axis positioning data and tool data,<ref>{{cite web |archive-date=2014-05-03 |url=http://www.machinetoolhelp.com/Applications/macro/system_variables.html |title=Fanuc macro system variables |access-date=2014-06-30 |archive-url=https://web.archive.org/web/20140503030834/http://www.machinetoolhelp.com/Applications/macro/system_variables.html }}</ref> via variables used by NC programs. These constructs make it easier to develop automation applications.


== Specific codes == == Extensions and variations ==
G-codes are also called preparatory codes, and are any word in a CNC program that begins with the letter "G". Generally it is a code telling the machine tool what type of action to perform, such as:
* Rapid move (transport the tool through space to the place where it is needed for cutting; do this as quickly as possible)
* Controlled feed move in a straight line or arc
* Series of controlled feed moves that would result in a hole being bored, a workpiece cut (routed) to a specific dimension, or a profile (contour) shape added to the edge of a workpiece
* Set tool information such as offset
* Switch coordinate systems


Extensions and variations have been added independently by control manufacturers and machine tool manufacturers, and operators of a specific controller must be aware of the differences between each manufacturer's product.
There are other codes; the type codes can be thought of like ] in a computer.


One standardized version of G-code, known as ''BCL'' (Binary Cutter Language), is used only on very few machines. Developed at MIT, BCL was developed to control CNC machines in terms of straight lines and arcs.<ref>{{Cite book|url=https://books.google.com/books?id=GE8vBQAAQBAJ&q=binary+cutter+language+gcode&pg=PA321|title=Information Technology Standards: Quest for the Common Byte.|last=Martin.|first=Libicki|date=1995|publisher=Elsevier Science|isbn=978-1-4832-9248-9|location=Burlington|page=321|oclc=895436474}}</ref>
===Letter addresses===
Some letter addresses are used only in milling or only in turning; most are used in both. '''Bold''' below are the letters seen most frequently throughout a program.


Some CNC machines use "conversational" programming, which is a ]-like programming mode that either hides G-code or completely bypasses the use of G-code. Some popular examples are Okuma's Advanced One Touch (AOT), Southwestern Industries' ProtoTRAK, Mazak's Mazatrol, Hurco's Ultimax and Winmax, Haas' Intuitive Programming System (IPS), and Mori Seiki's CAPS conversational software.
Sources: Smid<ref name="Smid2008">{{Harvnb|Smid|2008}}.</ref>; Green et al.<ref name="Greenetal1996">{{Harvnb|Green|1996|pp=1162–1226}}.</ref>


== See also ==
{| class="wikitable" border="1"
* ]
|-
* ]
! Variable !! Description !! Corollary info
* ]
|-
* ]
| valign="top" | {{Visible anchor|A}} || Absolute or incremental position of A axis (rotational axis around X axis) ||
|-
| valign="top" | {{Visible anchor|B}} || Absolute or incremental position of B axis (rotational axis around Y axis) ||
|-
| valign="top" | {{Visible anchor|C}} || Absolute or incremental position of C axis (rotational axis around Z axis) ||
|-
| valign="top" | {{Visible anchor|D}} || Defines diameter or radial offset used for cutter compensation. D is used for depth of cut on lathes. ||
|-
| valign="top" | {{Visible anchor|E}} || Precision feedrate for threading on lathes ||
|-
| valign="top" | {{Visible anchor|F}} || Defines ] ||
|-
| valign="top" | '''{{Visible anchor|G}}''' || Address for preparatory commands || G commands often tell the control what kind of motion is wanted (e.g., rapid positioning, linear feed, circular feed, fixed cycle) or what offset value to use.
|-
| valign="top" | {{Visible anchor|H}} || Defines tool length offset; <br> Incremental axis corresponding to C axis (e.g., on a turn-mill) ||
|-
| valign="top" | {{Visible anchor|I}} || Defines arc size in X axis for ] or ] arc commands. <br> Also used as a parameter within some fixed cycles. ||
|-
| valign="top" | {{Visible anchor|J}} || Defines arc size in Y axis for ] or ] arc commands. <br> Also used as a parameter within some fixed cycles. ||
|-
| valign="top" | {{Visible anchor|K}} || Defines arc size in Z axis for ] or ] arc commands. <br> Also used as a parameter within some fixed cycles, equal to ] address. ||
|-
| valign="top" | {{Visible anchor|L}} || Fixed cycle loop count; <br> Specification of what register to edit using ] || ''Fixed cycle loop count:'' Defines number of repetitions ("loops") of a fixed cycle at ''each'' position. Assumed to be 1 unless programmed with another integer. Sometimes the ] address is used instead of L. With incremental positioning (]), a series of equally spaced holes can be programmed as a loop rather than as individual positions. <br> ''] use:'' Specification of what register to edit (work offsets, tool radius offsets, tool length offsets, etc.).
|-
| valign="top" | '''{{Visible anchor|M}}''' || Miscellaneous function || Action code, auxiliary command; descriptions vary. Many M-codes call for machine functions, which is why people often say that the "M" stands for "machine", although it was not intended to.
|-
| valign="top" | {{Visible anchor|N}} || Line (block) number in program; <br> System parameter number to be changed using ] || ''Line (block) numbers:'' Optional, so often omitted. Necessary for certain tasks, such as ] ] address (to tell the control which block of the program to return to if not the default one) or ] statements (if the control supports those). ] numbering need not increment by 1 (for example, it can increment by 10, 20, or 1000) and can be used on every block or only in certain spots throughout a program. <br> ''System parameter number:'' ] allows changing of system parameters under program control.
|-
| valign="top" | {{Visible anchor|O}} || Program name || For example, O4501. For many years it was common for CNC control displays to use ] glyphs to ensure effortless distinction of letter "O" from digit "0". Today's GUI controls often have a choice of fonts, like a PC does.
|-
| valign="top" | {{Visible anchor|P}} || Serves as parameter address for various G and M codes ||
* With ], defines dwell time value.
* Also serves as a parameter in some canned cycles, representing dwell times or other variables.
* Also used in the calling and termination of subprograms. (With ], it specifies which subprogram to call; with ], it specifies which block number of the main program to return to.)
|-
| valign="top" | {{Visible anchor|Q}} || Peck increment in canned cycles || For example, ], ] (peck drilling cycles)
|-
| valign="top" | {{Visible anchor|R}} || Defines size of arc radius or defines retract height in canned cycles ||
|-
| valign="top" | {{Visible anchor|S}} || Defines ], either spindle speed or surface speed depending on mode || Data type = integer. In ] mode (which is usually the default), an integer after S is interpreted as a number of ] (rpm). In ] mode (CSS), an integer after S is interpreted as ]—sfm (]) or m/min (]). See also ]. On multifunction (turn-mill or mill-turn) machines, which spindle gets the input (main spindle or subspindles) is determined by other M codes.
|-
| valign="top" | {{Visible anchor|T}} || Tool selection || To understand how the T address works and how it interacts (or not) with ], one must study the various methods, such as lathe turret programming, ATC fixed tool selection, ATC random memory tool selection, the concept of "next tool waiting", and empty tools. Programming on any particular machine tool requires knowing which method that machine uses. Ways of obtaining this training are mentioned in the comments for ].
|-
| valign="top" | {{Visible anchor|U}} || Incremental axis corresponding to X axis (typically only lathe group A controls) <br> Also defines dwell time on some machines (instead of "]" or "]"). || In these controls, X and U obviate ] and ], respectively. On these lathes, G90 is instead a fixed cycle address for roughing.
|-
| valign="top" | {{Visible anchor|V}} || Incremental axis corresponding to Y axis || Until the 2000s, the V address was very rarely used, because most lathes that used U and W didn't have a Y-axis, so they didn't use V. (Green et al 1996<ref name="Greenetal1996"/> did not even list V in their table of addresses.) That is still often the case, although the proliferation of live lathe tooling and turn-mill machining has made V address usage less rare than it used to be (Smid 2008<ref name="Smid2008"/> shows an example). See also ].
|-
| valign="top" | {{Visible anchor|W}} || Incremental axis corresponding to Z axis (typically only lathe group A controls) || In these controls, Z and W obviate ] and ], respectively. On these lathes, G90 is instead a fixed cycle address for roughing.
|-
| valign="top" | '''{{Visible anchor|X}}''' || Absolute or incremental position of X axis. <br> Also defines dwell time on some machines (instead of "]" or "]"). ||
|-
| valign="top" | '''{{Visible anchor|Y}}''' || Absolute or incremental position of Y axis ||
|-
| valign="top" | '''{{Visible anchor|Z}}''' || Absolute or incremental position of Z axis || The main spindle's axis of rotation often determines which axis of a machine tool is labeled as Z.
|}


== References ==
===List of G-codes commonly found on Fanuc and similarly designed controls===
{{Reflist}}


== Bibliography ==
Sources: Smid<ref name="Smid2008" />; Green et al.<ref name="Greenetal1996" />

{| class="wikitable" border="1"
! Code !! Description !! Milling <br> ( M ) !! Turning <br> ( T ) !! Corollary info
|-
| valign="top" | {{Visible anchor|G00}} || Rapid positioning || M || T || On 2- or 3-axis moves, G00 (unlike ]) traditionally does not necessarily move in a single straight line between start point and end point. It moves each axis at its max speed until its vector is achieved. Shorter vector usually finishes first (given similar axis speeds). This matters because it may yield a dog-leg or hockey-stick motion, which the programmer needs to consider depending on what obstacles are nearby, to avoid a crash. Some machines offer interpolated rapids as a feature for ease of programming (safe to assume a straight line).
|-
| valign="top" | {{Visible anchor|G01}} || ] || M || T || The most common workhorse code for feeding during a cut. The program specs the start and end points, and the control automatically calculates (]) the intermediate points to pass through that will yield a straight line (hence "]"). The control then calculates the angular velocities at which to turn the axis ]s via their servomotors or stepper motors. The computer performs thousands of calculations per second, and the motors react quickly to each input. Thus the actual toolpath of the machining takes place with the given feedrate on a path that is accurately linear to within very small limits.
|-
| valign="top" | {{Visible anchor|G02}} || Circular interpolation, clockwise || M || T || Very similar in concept to G01. Again, the control ] intermediate points and commands the servo- or stepper motors to rotate the amount needed for the leadscrew to translate the motion to the correct tool tip positioning. This process repeated thousands of times per minute generates the desired toolpath. In the case of G02, the interpolation generates a circle rather than a line. As with G01, the actual toolpath of the machining takes place with the given feedrate on a path that accurately matches the ideal (in G02's case, a circle) to within very small limits. In fact, the interpolation is so precise (when all conditions are correct) that milling an interpolated circle can obviate operations such as drilling, and often even fine boring. On most controls you cannot start ] or ] in ] or ] modes. You must already have compensated in an earlier ] block. Often a short linear lead-in movement will be programmed, merely to allow cutter compensation before the main event, the circle-cutting, begins.
|-
| valign="top" | {{Visible anchor|G03}} || Circular interpolation, counterclockwise || M || T || Same corollary info as for G02.
|-
| valign="top" | {{Visible anchor|G04}} || Dwell || M || T || Takes an address for dwell period (may be ], ], or ]). The dwell period is specified in '''milliseconds'''.
|-
| valign="top" | {{Visible anchor|G05}} P10000 || High-precision contour control (HPCC) || M || &nbsp; || Uses a deep look-ahead ] and simulation processing to provide better axis movement acceleration and deceleration during contour milling
|-
| valign="top" | {{Visible anchor|G05.1 Q1.}} || ] Nano contour control || M || &nbsp; || Uses a deep look-ahead ] and simulation processing to provide better axis movement acceleration and deceleration during contour milling
|-
| valign="top" | {{Visible anchor|G07}} || Imaginary axis designation || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G09}} || Exact stop check || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G10}} || Programmable data input || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G11}} || Data write cancel || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G12}} || Full-circle interpolation, clockwise || M || &nbsp; || Fixed cycle for ease of programming 360° circular interpolation with blend-radius lead-in and lead-out. Not standard on Fanuc controls.
|-
| valign="top" | {{Visible anchor|G13}} || Full-circle interpolation, counterclockwise || M || &nbsp; || Fixed cycle for ease of programming 360° circular interpolation with blend-radius lead-in and lead-out. Not standard on Fanuc controls.
|-
| valign="top" | {{Visible anchor|G17}} || XY plane selection || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G18}} || ZX plane selection || M || T || On most CNC lathes (built 1960s to 2000s), ZX is the only available plane, so no ] to ] codes are used. This is now changing as the era begins in which live tooling, multitask/multifunction, and mill-turn/turn-mill gradually become the "new normal". But the simpler, traditional form factor will probably not disappear—just move over to make room for the newer configurations. See also ] address.
|-
| valign="top" | {{Visible anchor|G19}} || YZ plane selection || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G20}} || Programming in ]es || M || T || Somewhat uncommon except in USA and (to lesser extent) Canada and UK. However, in the global marketplace, competence with both G20 and G21 always stands some chance of being necessary at any time. The usual minimum increment in G20 is one ten-thousandth of an inch (0.0001"), which is a larger distance than the usual minimum increment in G21 (one thousandth of a millimeter, .001&nbsp;mm, that is, one ]). This physical difference sometimes favors G21 programming.
|-
| valign="top" | {{Visible anchor|G21}} || Programming in ]s (mm) || M || T || Prevalent worldwide. However, in the global marketplace, competence with both G20 and G21 always stands some chance of being necessary at any time.
|-
| valign="top" | {{Visible anchor|G28}} || Return to home position (machine zero, aka machine reference point) || M || T || Takes X Y Z addresses which define the intermediate point that the tool tip will pass through on its way home to machine zero. They are in terms of part zero (aka program zero), NOT machine zero.
|-
| valign="top" | {{Visible anchor|G30}} || Return to secondary home position (machine zero, aka machine reference point) || M || T || Takes a P address specifying ''which'' machine zero point is desired, ''if'' the machine has several secondary points (P1 to P4). Takes X Y Z addresses which define the intermediate point that the tool tip will pass through on its way home to machine zero. They are in terms of part zero (aka program zero), NOT machine zero.
|-
| valign="top" | {{Visible anchor|G31}} || Skip function (used for probes and tool length measurement systems) || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G32}} || Single-point threading, longhand style (if not using a cycle, e.g., ]) || &nbsp; || T || Similar to ] linear interpolation, except with automatic spindle synchronization for ].
|-
| valign="top" | {{Visible anchor|G33}} || Constant-] threading || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G33}} || Single-point threading, longhand style (if not using a cycle, e.g., ]) || &nbsp; || T || Some lathe controls assign this mode to G33 rather than G32.
|-
| valign="top" | {{Visible anchor|G34}} || Variable-pitch threading || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G40}} || Tool radius compensation off || M || T || Cancels G41 or G42.
|-
| valign="top" | {{Visible anchor|G41}} || Tool radius compensation left || M || T || '''Milling:''' Given righthand-helix cutter and ] spindle direction, G41 corresponds to ]. Takes an address (] or ]) that calls an offset register value for radius. <br> '''Turning:''' Often needs no D or H address on lathes, because whatever tool is active automatically calls its geometry offsets with it. (Each turret station is bound to its geometry offset register.)

G41 and G42 for milling has become less frequently used since CAM programming has become more common. CAM systems allow the user to program as if with a zero-diameter cutter. The fundamental concept of cutter radius compensation is still in play (i.e., that the surface produced will be distance R away from the cutter center), but the programming mindset is different; the human does not choreograph the toolpath with conscious, painstaking attention to G41, G42, and G40, because the CAM software takes care of it.
|-
| valign="top" | {{Visible anchor|G42}} || Tool radius compensation right || M || T || Similar corollary info as for G41. Given righthand-helix cutter and M03 spindle direction, G42 corresponds to ].

See also the comments for ].
|-
| valign="top" | {{Visible anchor|G43}} || Tool height offset compensation negative || M || &nbsp; || Takes an address, usually H, to call the tool length offset register value. The value is ''negative'' because it will be ''added'' to the gauge line position. G43 is the commonly used version (vs G44).
|-
| valign="top" | {{Visible anchor|G44}} || Tool height offset compensation positive || M || &nbsp; || Takes an address, usually H, to call the tool length offset register value. The value is ''positive'' because it will be ''subtracted'' from the gauge line position. G44 is the seldom-used version (vs G43).
|-
| valign="top" | {{Visible anchor|G45}} || Axis offset single increase || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G46}} || Axis offset single decrease || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G47}} || Axis offset double increase || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G48}} || Axis offset double decrease || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G49}} || Tool length offset compensation cancel || M || &nbsp; || Cancels ] or ].
|-
| valign="top" | {{Visible anchor|G50}} || Define the maximum spindle speed || &nbsp; || T || Takes an ] address integer which is interpreted as rpm. Without this feature, ] mode (CSS) would rev the spindle to "wide open throttle" when closely approaching the axis of rotation.
|-
| G50 || Scaling function cancel || M || &nbsp; || &nbsp;
|-
| G50 || Position register (programming of vector from part zero to tool tip) || &nbsp; || T || Position register is one of the original methods to relate the part (program) coordinate system to the tool position, which indirectly relates it to the machine coordinate system, the only position the control really "knows". Not commonly programmed anymore because ] (WCSs) are a better, newer method. Called via G50 for turning, ] for milling. Those G addresses also have alternate meanings (which see). Position register can still be useful for datum shift programming.
|-
| valign="top" | {{Visible anchor|G52}} || Local coordinate system (LCS) || M || &nbsp; || Temporarily shifts program zero to a new location. This simplifies programming in some cases.
|-
| valign="top" | {{Visible anchor|G53}} || Machine coordinate system || M || T || Takes absolute coordinates (X,Y,Z,A,B,C) with reference to machine zero rather than program zero. Can be helpful for tool changes. Nonmodal and absolute only. Subsequent blocks are interpreted as "back to ]" even if it is not explicitly programmed.
|-
| valign="top" | {{Visible anchor|G54 to G59}} || Work coordinate systems (WCSs) || M || T || Have largely replaced position register (] and ]). Each tuple of axis offsets relates program zero directly to machine zero. Standard is 6 tuples (G54 to G59), with optional extensibility to 48 more via G54.1 P1 to P48.
|-
| valign="top" | {{Visible anchor|G54.1 P1 to P48}} || Extended work coordinate systems || M || T || Up to 48 more WCSs besides the 6 provided as standard by G54 to G59. Note floating-point extension of G-code data type (formerly all integers). Other examples have also evolved (e.g., ]). Modern controls have the ] to handle it.
|-
| valign="top" | {{Visible anchor|G70}} || Fixed cycle, multiple repetitive cycle, for finishing (including contours) || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G71}} || Fixed cycle, multiple repetitive cycle, for roughing (Z-axis emphasis) || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G72}} || Fixed cycle, multiple repetitive cycle, for roughing (X-axis emphasis) || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G73}} || Fixed cycle, multiple repetitive cycle, for roughing, with pattern repetition || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G73}} || Peck drilling cycle for milling - high-speed (NO full retraction from pecks) || M || &nbsp; || Retracts only as far as a clearance increment (system parameter). For when chipbreaking is the main concern, but chip clogging of flutes is not.
|-
| valign="top" | {{Visible anchor|G74}} || Peck drilling cycle for turning || &nbsp; || T || &nbsp;
|-
| G74 || Tapping cycle for milling, ], M04 spindle direction || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G75}} || Peck grooving cycle for turning || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G76}} || Fine boring cycle for milling || M || &nbsp; || &nbsp;
|-
| G76 || Threading cycle for turning, multiple repetitive cycle || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|G80}} || Cancel canned cycle || M || T || '''Milling:''' Cancels all cycles such as ], ], ], etc. Z-axis returns either to Z-initial level or R-level, as programmed (] or ], respectively). <br> '''Turning:''' Usually not needed on lathes, because a new group-1 G address (] to ]) cancels whatever cycle was active.
|-
| valign="top" | {{Visible anchor|G81}} || Simple drilling cycle || M || &nbsp; || No dwell built in
|-
| valign="top" | {{Visible anchor|G82}} || Drilling cycle with dwell || M || &nbsp; || Dwells at hole bottom (Z-depth) for the number of '''milliseconds''' specified by the ] address. Good for when hole bottom finish matters.
|-
| valign="top" | {{Visible anchor|G83}} || Peck drilling cycle (full retraction from pecks) || M || &nbsp; || Returns to R-level after each peck. Good for clearing flutes of ].
|-
| valign="top" | {{Visible anchor|G84}} || ] cycle, ], ] spindle direction || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G84.2}} || Tapping cycle, righthand thread, ] spindle direction, rigid toolholder || M || &nbsp; || &nbsp;
|-
| valign="top" | {{Visible anchor|G90}} || Absolute programming || M || T (B) || Positioning defined with reference to part zero. <br> '''Milling:''' Always as above. <br> '''Turning:''' Sometimes as above (Fanuc group type B and similarly designed), but on most lathes (Fanuc group type A and similarly designed), G90/G91 are not used for absolute/incremental modes. Instead, ] and ] are the incremental addresses and ] and ] are the absolute addresses. On these lathes, G90 is instead a fixed cycle address for roughing.
|-
| G90 || Fixed cycle, simple cycle, for roughing (Z-axis emphasis) || &nbsp; || T (A) || When not serving for absolute programming (above)
|-
| valign="top" | {{Visible anchor|G91}} || Incremental programming || M || T (B) || Positioning defined with reference to previous position. <br> '''Milling:''' Always as above. <br> '''Turning:''' Sometimes as above (Fanuc group type B and similarly designed), but on most lathes (Fanuc group type A and similarly designed), G90/G91 are not used for absolute/incremental modes. Instead, ] and ] are the incremental addresses and ] and ] are the absolute addresses. On these lathes, G90 is a fixed cycle address for roughing.
|-
| valign="top" | {{Visible anchor|G92}} || Position register (programming of vector from part zero to tool tip) || M || T (B) || Same corollary info as at ] position register. <br> '''Milling:''' Always as above. <br> '''Turning:''' Sometimes as above (Fanuc group type B and similarly designed), but on most lathes (Fanuc group type A and similarly designed), position register is ].
|-
| G92 || Threading cycle, simple cycle || &nbsp; || T (A) || &nbsp;
|-
| valign="top" | {{Visible anchor|G94}} || Feedrate per minute || M || T (B) || On group type A lathes, feedrate per minute is ].
|-
| G94 || Fixed cycle, simple cycle, for roughing (]-axis emphasis) || &nbsp; || T (A) || When not serving for feedrate per minute (above)
|-
| valign="top" | {{Visible anchor|G95}} || Feedrate per revolution || M || T (B) || On group type A lathes, feedrate per revolution is ].
|-
| valign="top" | {{Visible anchor|G96}} || Constant surface speed (CSS) || &nbsp; || T || Varies spindle speed automatically to achieve a constant surface speed. See ]. Takes an ] address integer, which is interpreted as ] in ] mode or as m/min in ] mode.
|-
| valign="top" | {{Visible anchor|G97}} || Constant spindle speed || M || T || Takes an S address integer, which is interpreted as rev/min (rpm). The default speed mode per system parameter if no mode is programmed.
|-
| valign="top" | {{Visible anchor|G98}} || Return to initial Z level in canned cycle || M || &nbsp; || &nbsp;
|-
| G98 || Feedrate per minute (group type A) || &nbsp; || T (A) || Feedrate per minute is ] on group type B.
|-
| valign="top" | {{Visible anchor|G99}} || Return to R level in canned cycle || M || &nbsp; || &nbsp;
|-
| G99 || Feedrate per revolution (group type A) || &nbsp; || T (A) || Feedrate per revolution is ] on group type B.
|-
|}

===List of M-codes commonly found on Fanuc and similarly designed controls===

Sources: Smid<ref name="Smid2008" />; Green et al.<ref name="Greenetal1996" />

{| class="wikitable" border="1"
! Code&nbsp;&nbsp; !! Description !! Milling <br> ( M ) !! Turning <br> ( T ) !! Corollary info
|-
| valign="top" | {{Visible anchor|M00}} || Compulsory stop || M || T || Non-optional—machine will always stop upon reaching M00 in the program execution.
|-
| valign="top" | {{Visible anchor|M01}} || Optional stop || M || T || Machine will only stop at M01 if operator has pushed the optional stop button.
|-
| valign="top" | {{Visible anchor|M02}} || End of program || M || T || No return to program top; may or may not reset register values.
|-
| valign="top" | {{Visible anchor|M03}} || Spindle on (clockwise rotation) || M || T || The speed of the spindle is determined by the address ], in either ] (] mode; default) or ] or meters per minute (] mode under either ] or ]). The ] can be used to determine which direction is clockwise and which direction is counter-clockwise.
Right-hand-helix screws moving in the tightening direction (and right-hand-helix flutes spinning in the cutting direction) are defined as moving in the M03 direction, and are labeled "clockwise" by convention. The M03 direction is always M03 regardless of local vantage point and local CW/CCW distinction.
|-
| valign="top" | {{Visible anchor|M04}} || Spindle on (counterclockwise rotation) || M || T || See comment above at M03.
|-
| valign="top" | {{Visible anchor|M05}} || Spindle stop || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M06}} || Automatic tool change (ATC) || M || T (some-times) || Many lathes do not use M06 because the ] address itself indexes the turret. <br> Programming on any particular machine tool requires knowing which method that machine uses. To understand how the T address works and how it interacts (or not) with M06, one must study the various methods, such as lathe turret programming, ATC fixed tool selection, ATC random memory tool selection, the concept of "next tool waiting", and empty tools. These concepts are taught in textbooks such as Smid,<ref name="Smid2008" /> and online multimedia (videos, simulators, etc); all of these teaching resources are usually ]ed to pay back the costs of their development. They are used in training classes for operators, both on-site and remotely (e.g., ]).
|-
| valign="top" | {{Visible anchor|M07}} || ] on (mist) || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M08}} || Coolant on (flood) || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M09}} || Coolant off || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M10}} || Pallet clamp on || M || &nbsp; || For machining centers with pallet changers
|-
| valign="top" | {{Visible anchor|M11}} || Pallet clamp off || M || &nbsp; || For machining centers with pallet changers
|-
| valign="top" | {{Visible anchor|M13}} || Spindle on (clockwise rotation) and coolant on (flood) || M || &nbsp; || This one M-code does the work of both ] and ]. It is not unusual for specific machine models to have such combined commands, which make for shorter, more quickly written programs.
|-
| valign="top" | {{Visible anchor|M19}} || Spindle orientation || M || T || Spindle orientation is more often called within cycles (automatically) or during setup (manually), but it is also available under program control via '''M19'''. The abbreviation OSS (oriented spindle stop) may be seen in reference to an oriented stop within cycles.

The relevance of spindle orientation has increased as technology has advanced. Although 4- and 5-axis contour milling and CNC ] have depended on spindle position encoders for decades, before the advent of widespread live tooling and mill-turn/turn-mill systems, it was seldom relevant in "regular" (non-"special") machining for the operator (as opposed to the machine) to know the angular orientation of a spindle except for within a few restricted contexts (such as ], or ] fine boring cycles with choreographed tool retraction). Most milling of features indexed around a turned workpiece was accomplished with separate operations on ] setups; in a sense, indexing heads were invented as separate pieces of equipment, to be used in separate operations, which could provide precise spindle orientation in a world where it otherwise mostly didn't exist (and didn't need to). But as CAD/CAM and multiaxis CNC machining with multiple rotary-cutter axes becomes the norm, even for "regular" (non-"special") applications, machinists now frequently care about stepping just about ''any'' spindle through its 360° with precision.
|-
| valign="top" | {{Visible anchor|M21}} || Mirror, ]-axis || M || &nbsp; || &nbsp;
|-
| M21 || Tailstock forward || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M22}} || Mirror, ]-axis || M || &nbsp; || &nbsp;
|-
| M22 || Tailstock backward || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M23}} || Mirror OFF || M || &nbsp; || &nbsp;
|-
| M23 || Thread gradual pullout ON || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M24}} || Thread gradual pullout OFF || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M30}} || End of program with return to program top || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M41}} || Gear select - gear&nbsp;1 || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M42}} || Gear select - gear&nbsp;2 || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M43}} || Gear select - gear&nbsp;3 || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M44}} || Gear select - gear&nbsp;4 || &nbsp; || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M48}} || Feedrate override allowed || M || T || &nbsp;
|-
| valign="top" | {{Visible anchor|M49}} || Feedrate override NOT allowed || M || T || This rule is also called (automatically) within tapping cycles or single-point threading cycles, where feed is precisely correlated to speed. Same with spindle speed override and feed hold button.
|-
| valign="top" | {{Visible anchor|M52}} || Unload Last tool from spindle || M || T || Also empty spindle.
|-
| valign="top" | {{Visible anchor|M60}} || Automatic pallet change (APC) || M || &nbsp; || For machining centers with pallet changers
|-
| valign="top" | {{Visible anchor|M98}} || Subprogram call || M || T || Takes an address ] to specify which subprogram to call, for example, "M98 P8979" calls subprogram O8979.
|-
| valign="top" | {{Visible anchor|M99}} || Subprogram end || M || T || Usually placed at end of subprogram, where it returns execution control to the main program. The default is that control returns to the block following the M98 call in the main program. Return to a different block number can be specified by a P address. M99 can also be used in main program with block skip for endless loop of main program on bar work on lathes (until operator toggles block skip).
|-
|}

==Example program==
]

This is a generic program that demonstrates the use of G-Code to turn a 1" diameter X 1" long part. Assume that a bar of material is in the machine and that the bar is slightly oversized in length and diameter and that the bar protrudes by more than 1" from the face of the chuck. (Caution: This is generic, it might not work on any real machine! Pay particular attention to point 5 below.)
{{clear}}

{| class="wikitable"
|+ Sample
!Line
!Code
!Description

|-
|%|| ||
|-
|O4968|| || (Sample face and turn program)
|-
|N01||M216 || (Turn on load monitor)
|-
|N02||G20 G90 G54 D200 G40|| (Inch units. Absolute mode. Call work offset values. Moving coordinate system to the location specified in the register D200. Cancel any existing tool radius offset.)
|-
|N03||G50 S2000 || (Set maximum spindle speed rev/min - preparing for G96 CSS coming soon)
|-
|N04||M01|| (Optional stop)
|-
|N05||T0300 || (Index turret to tool 3. Clear wear offset (00).)
|-
|N06||G96 S854 M42 M03 M08 || (Constant surface speed , 854 sfm, select spindle gear, start spindle CW rotation, turn on the coolant flood)
|-
|N07||G41 G00 X1.1 Z1.1 T0303 || (Call tool radius offset. Call tool wear offset. Rapid feed to a point ''about'' 0.100" from the end of the bar and 0.050" from the side)
|-
|N08||G01 Z1.0 F.05 || (Feed in horizontally until the tool is standing 1" from the datum i.e. program Z-zero)
|-
|N09||X-0.002 || (Feed down until the tool is slightly past center, thus facing the end of the bar)
|-
|N10||G00 Z1.1 || (Rapid feed 0.1" away from the end of the bar - clear the part)
|-
|N11||X1.0 || (Rapid feed up until the tool is standing at the finished OD)
|-
|N12||G01 Z0.0 F.05 || (Feed in horizontally cutting the bar to 1" diameter all the way to the datum, feeding at 0.050" per revolution)
|-
|N13||G00 X1.1 M05 M09 || (Clear the part, stop the spindle, turn off the coolant)
|-
|N14||G91 G28 X0 || (Home X axis - return to machine X-zero passing through no intermediate X point )
|-
|N15||G91 G28 Z0 || (Home Z axis - return to machine Z-zero passing through no intermediate Z point )
|-
|N16||G90 M215 || (Return to absolute mode. Turn off load monitor)
|-
|N17||M30 || (Program stop, rewind to beginning of program)
|-
|%|| ||
|}

Several points to note:

# There is room for some programming style, even in this short program. The grouping of codes in line N06 could have been put on multiple lines. Doing so may have made it easier to follow program execution.
# Many codes are "modal", meaning that they stay in effect until they are cancelled or replaced by a contradictory code. For example, once variable speed cutting (CSS) had been selected (G96), it stayed in effect until the end of the program. In operation, the spindle speed would increase as the tool neared the center of the work in order to maintain a constant surface speed. Similarly, once rapid feed was selected (G00), all tool movements would be rapid until a feed rate code (G01, G02, G03) was selected.
# It is common practice to use a load monitor with CNC machinery. The load monitor will stop the machine if the spindle or feed loads exceed a preset value that is set during the set-up operation. The jobs of the load monitor are various:
## Prevent machine damage in the event of tool breakage or a programming mistake.
### This is especially important because it allows safe "lights-out machining", in which the operators set up the job and start it running during the day, then go home for the night, leaving the machines running and cutting parts during the night. Because no human is around to hear, see, or smell a problem such as a broken tool, the load monitor serves an important sentry duty. When it senses overload condition, which semantically suggests a dull or broken tool, it commands a stop to the machining. Technology is available nowadays to send an alert to someone remotely (e.g., the sleeping owner, operator, or owner-operator) if desired, which can allow them to come intercede and get production going again, then leave once more. This can be the difference between profitability or loss on some jobs, because lights-out machining reduces labor hours per part.
## Warn of a tool that is becoming dull and needs to be replaced or sharpened. Thus an operator who is busy tending multiple machines will be told by a machine, essentially, "Hey, pause what you're doing over there, and come attend to a need over here."
# It is common practice to bring the tool in rapidly to a "safe" point that is close to the part - in this case 0.1" away - and then start feeding the tool. How close that "safe" distance is, depends on the skill of the programmer and maximum material condition for the raw stock.
# If the program is wrong, there is a high probability that the machine will ''crash'', or ram the tool into the part under high power. This can be costly, especially in newer machining centers. It is possible to intersperse the program with optional stops (M01 code) which allow the program to be run piecemeal for testing purposes. The optional stops remain in the program but they are skipped during the normal running of the machine. Fortunately, most CAD/CAM software ships with CNC simulators that will display the movement of the tool as the program executes. Many modern CNC machines also allow programmers to execute the program in a simulation mode and observe the operating parameters of the machine at a particular execution point. This enables programmers to discover semantic errors (as opposed to syntax errors) before losing material or tools to an incorrect program. Depending on the size of the part, wax blocks may be used for testing purposes as well.
# For pedagogical purposes, line numbers have been included in the program above. They are usually not necessary for operation of a machine, so they are seldom used in industry. However, if branching or looping statements are used in the code, then line numbers may well be included as the target of those statements (e.g. GOTO N99).
# Some machines do not allow multiple M codes in the same line.

==Programming environments==
G-code's programming environments have evolved in parallel with those of general programming—from the earliest environments (e.g., writing a program with a pencil, typing it into a tape puncher) to the latest environments that ] CAD (]), CAM (]), and richly featured G-code editors. (G-code editors are analogous to ]s, using colors and indents semantically to aid the user in ways that basic ]s can't. CAM packages are analogous to ] in general programming.)

Two high-level paradigm shifts have been (1) abandoning "manual programming" (with nothing but a pencil or text editor and a human mind) for ] systems that generate G-code automatically via postprocessors (analogous to the development of ] techniques in general programming), and (2) abandoning hardcoded constructs for parametric ones (analogous to the difference in general programming between hardcoding a constant into an equation versus declaring it a variable and assigning new values to it at will; and to the ] approach in general). Macro (parametric) CNC programming uses human-friendly variable names, ]s, and loop structures much as general programming does, to capture information and logic with machine-readable semantics. Whereas older manual CNC programming could only describe particular instances of parts in numeric form, parametric CAM programming describes abstractions which can be flowed with ease into a wide variety of instances. The difference has many analogues, both from before the computing era and from after its advent, such as (1) creating text as bitmaps versus using ] with ]s; (2) the abstraction level of tabulated ]s, with many part dash numbers parametrically defined by the one same drawing and a parameter table; or (3) the way that ] passed through a phase of using content markup for presentation purposes, then matured toward the ] model. In all of these cases, a higher layer of abstraction was introduced in order to pursue what was missing semantically.

] reflects the same theme, which can be viewed as yet another step along a path that started with the development of machine tools, jigs and fixtures, and numerical control, which all sought to "build the skill into the tool". Recent developments of G-code and STEP-NC aim to build the information and semantics into the tool. The idea itself is not new; from the beginning of numerical control, the concept of an end-to-end CAD/CAM environment was the goal of such early technologies as ] and ]. Those efforts were fine for huge corporations like GM and Boeing. However, for ], there had to be an era in which the simpler implementations of NC, with relatively primitive "connect-the-dots" G-code and manual programming, ruled the day until CAD/CAM could improve and disseminate throughout the economy.

Any machine tool with a great number of axes, spindles, and tool stations is difficult to program well manually. It has been done over the years, but not easily. This challenge has existed for decades in CNC screw machine and rotary transfer programming, and it now also arises with today's newer machining centers called "turn-mills", "mill-turns", "multitasking machines", and "multifunction machines". Now that ] systems are widely used, CNC programming (such as with G-code) requires CAD/CAM (as opposed to manual programming) to be practical and competitive in the market segments served by these classes of machines.<ref name="MMS_2010-12-20_CAM_Sys">{{Citation |last=MMS editorial staff |date=2010-12-20 |title=CAM system simplifies Swiss-type lathe programming |journal=Modern Machine Shop |volume=83 |issue=8 |pages=100–105 |url=http://www.mmsonline.com/articles/cam-system-simplifies-swiss-type-lathe-programming |doi= |id= |postscript=. ''Online ahead of print.'' }}</ref> As Smid says, "Combine all these axes with some additional features, and the amount of knowledge required to succeed is quite overwhelming, to say the least."<ref name="Smid2008p457">{{Harvnb|Smid|2008|p=457}}.</ref> At the same time, however, programmers still must thoroughly understand the principles of manual programming and must think critically and second-guess some aspects of the software's decisions.

{{pov-section|date=November 2011}}
Since about the mid-2000s, the era has finally arrived when conventional wisdom, among the hasty or incompletely informed, has begun to declare the death of manual programming (writing lines of G-code without CAM assistance). In this view, manual programming is a thing of the past. However, this is clearly not accurate; although it is true that plenty of programming can and does take place nowadays among people who are rusty on, or incapable of, manual programming, it is not true that ''all'' CNC programming can be done, or done ''well'' or ''efficiently'', without being able to speak the language of G-code.<ref name="Lynch_MMS_2010-01-18">{{Citation |last=Lynch |first=Mike |date=2010-01-18 |title=When programmers should know G code |journal=Modern Machine Shop |edition=online |url=http://www.mmsonline.com/columns/when-programmers-should-know-g-code |doi= |id= |ref=harv |postscript=.}}</ref><ref name="Lynch_MMS_2011-10-19">{{Citation |last=Lynch |first=Mike |date=2011-10-19 |title=Five CNC myths and misconceptions |journal=Modern Machine Shop |edition=online |url=http://www.mmsonline.com/columns/five-cnc-myths-and-misconceptions |doi= |id= |ref=harv |postscript=.}}</ref> Tailoring and refining the CNC program at the machine is one of the main reasons why someone who knows G-code well has a real advantage over someone who must send the whole program back to CAM, explain what's needed (and why) to the CAM user, and hope that the CAM user has adequate machining knowledge to know how to make the right tweaks.

==Etymology==
Students and hobbyists have pointed out over the years that the term "G-code" referring to the language overall (using the ] sense of "code") is imprecise. It comes ]ically from the literal sense of the term, referring to one letter address among many in the language (G address, for preparatory commands) and to the specific codes (] sense) that can be formed with it (for example, G00, G01, G28). But every letter of the English alphabet is ] (although some letters' use is less common), so the name seems unfitting to people searching for strictly logical etymology. Nevertheless, the general sense of the term is indelibly established as the common name of the language.

The resistance among some users to the name "G programming language" may come from the fact that historically G-code was not a "language" in the same sense that ] or ] are—that is, ]s. However, G-code has by now been ] to the point that it can function as a high-level language, so the objection, to the extent that it still exists, rests now only on what people grew used to hearing in decades past.

==See also==
===Extended developments===
*] (DNC)
*]
*]
===Similar concepts===
*]
===Concerns during application===
*], cutter compensation, offset parameters
*]s

==References==
{{Reflist|30em}}

==Bibliography==
* {{MachinerysHandbook25e}} * {{MachinerysHandbook25e}}
* {{Smid2008}} * {{Smid2008}}
* {{Smid2010}}
* {{Citation |last=Smid |first=Peter |year=2004 |title=Fanuc CNC Custom Macros |publisher=Industrial Press |url=https://books.google.com/books?id=YKvH-zYd3VwC&pg=PR11 |isbn=978-0-8311-3157-9 |postscript=.}}


==External links== == External links ==
*
*
* {{Citation |last1=Kramer |first1=T. R. |last2=Proctor |first2=F. M. |last3=Messina |first3=E. R. |title=The NIST RS274NGC Interpreter – Version 3 |date=1 Aug 2000 |id=NISTIR 6556 |journal=] |url=https://www.nist.gov/manuscript-publication-search.cfm?pub_id=823374 |ref=none}}
*
* http://museum.mit.edu/150/86 {{Webarchive|url=https://web.archive.org/web/20160319102859/http://museum.mit.edu/150/86 |date=2016-03-19 }} Has several links (including history of MIT Servo Lab)
*
* at reprap.org
* also available as a
*
* http://museum.mit.edu/150/86 Has several links (including history of MIT Servo Lab)
*
*
*
*


{{Metalworking navbox|machopen}} {{Metalworking navbox|machopen}}


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Latest revision as of 00:15, 17 December 2024

Primary programming language used in CNC For other uses, see G-code (disambiguation) and G programming language (disambiguation). "RS-274" redirects here. For the photoplotter format, see Gerber format.
G-code
ParadigmProcedural, imperative
Designed byMassachusetts Institute of Technology
DeveloperElectronic Industries Association (RS-274), International Organization for Standardization (ISO-6983)
First appeared1963 (1963) (RS-274)
Filename extensions.gcode, .mpt, .mpf, .nc and several others
Major implementations
Numerous; mainly Siemens Sinumerik, FANUC, Haas, Heidenhain, Mazak, Okuma

G-code (also RS-274) is the most widely used computer numerical control (CNC) and 3D printing programming language. It is used mainly in computer-aided manufacturing to control automated machine tools, as well as for 3D-printer slicer applications. The G stands for geometry. G-code has many variants.

G-code instructions are provided to a machine controller (industrial computer) that tells the motors where to move, how fast to move, and what path to follow. The two most common situations are that, within a machine tool such as a lathe or mill, a cutting tool is moved according to these instructions through a toolpath cutting away material to leave only the finished workpiece and/or an unfinished workpiece is precisely positioned in any of up to nine axes around the three dimensions relative to a toolpath and, either or both can move relative to each other. The same concept also extends to noncutting tools such as forming or burnishing tools, photoplotting, additive methods such as 3D printing, and measuring instruments.

History

The first implementation of a numerical control programming language was developed at the MIT Servomechanisms Laboratory in the 1950s. In the decades that followed, many implementations were developed by numerous organizations, both commercial and noncommercial. Elements of G-code had often been used in these implementations. The first standardized version of G-code used in the United States, RS-274, was published in 1963 by the Electronic Industries Alliance (EIA; then known as Electronic Industries Association). In 1974, EIA approved RS-274-C, which merged RS-273 (variable block for positioning and straight cut) and RS-274-B (variable block for contouring and contouring/positioning). A final revision of RS-274 was approved in 1979, as RS-274-D. In other countries, the standard ISO 6983 (finalized in 1982) is often used, but many European countries use other standards. For example, DIN 66025 is used in Germany, and PN-73M-55256 and PN-93/M-55251 were formerly used in Poland.

During the 1970s through 1990s, many CNC machine tool builders attempted to overcome compatibility difficulties by standardizing on machine tool controllers built by Fanuc. Siemens was another market dominator in CNC controls, especially in Europe. In the 2010s, controller differences and incompatibility were mitigated with the widespread adoption of CAD/CAM applications that were capable of outputting machine operations in the appropriate G-code for a specific machine through a software tool called a post-processor (sometimes shortened to just a "post").

Syntax

G-code began as a limited language that lacked constructs such as loops, conditional operators, and programmer-declared variables with natural-word-including names (or the expressions in which to use them). It was unable to encode logic but was just a way to "connect the dots" where the programmer figured out many of the dots' locations longhand. The latest implementations of G-code include macro language capabilities somewhat closer to a high-level programming language. Additionally, all primary manufacturers (e.g., Fanuc, Siemens, Heidenhain) provide access to programmable logic controller (PLC) data, such as axis positioning data and tool data, via variables used by NC programs. These constructs make it easier to develop automation applications.

Extensions and variations

Extensions and variations have been added independently by control manufacturers and machine tool manufacturers, and operators of a specific controller must be aware of the differences between each manufacturer's product.

One standardized version of G-code, known as BCL (Binary Cutter Language), is used only on very few machines. Developed at MIT, BCL was developed to control CNC machines in terms of straight lines and arcs.

Some CNC machines use "conversational" programming, which is a wizard-like programming mode that either hides G-code or completely bypasses the use of G-code. Some popular examples are Okuma's Advanced One Touch (AOT), Southwestern Industries' ProtoTRAK, Mazak's Mazatrol, Hurco's Ultimax and Winmax, Haas' Intuitive Programming System (IPS), and Mori Seiki's CAPS conversational software.

See also

References

  1. Karlo Apro (2008). Secrets of 5-Axis Machining. Industrial Press Inc. ISBN 0-8311-3375-9.
  2. Xu, Xun (2009). Integrating Advanced Computer-aided Design, Manufacturing, and Numerical Control: Principles and Implementations. Information Science Reference. p. 166. ISBN 978-1-59904-716-4 – via Google Books.
  3. Harik, Ramy; Thorsten Wuest (2019). Introduction to Advanced Manufacturing. SAE International. p. 116. ISBN 978-0-7680-9096-3 – via Google Books.
  4. Evans, John M. Jr. (1976). National Bureau of Standards Information Report (NBSIR) 76-1094 (R): Standards for Computer Aided Manufacturing (PDF). National Bureau of Standards. p. 43.
  5. Schenck, John P. (January 1, 1998). "Understanding common CNC protocols". Wood & Wood Products. 103 (1). Vance Publishing: 43 – via Gale.
  6. EIA Standard RS-274-D Interchangeable Variable Block Data Format for Positioning, Contouring, and Contouring/Positioning Numerically Controlled Machines, Washington D.C.: Electronic Industries Association, February 1979
  7. Stark, J.; V. K. Nguyen (2009). "STEP-compliant CNC Systems, Present and Future Directions". In Xu, Xun; Andrew Yeh Ching Nee (eds.). Advanced Design and Manufacturing Based on STEP. Springer London. p. 216. ISBN 978-1-84882-739-4 – via Google Books.
  8. "Fanuc macro system variables". Archived from the original on 2014-05-03. Retrieved 2014-06-30.
  9. Martin., Libicki (1995). Information Technology Standards: Quest for the Common Byte. Burlington: Elsevier Science. p. 321. ISBN 978-1-4832-9248-9. OCLC 895436474.

Bibliography

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