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G-code instructions are provided to a [[Programmable logic controller|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 [[Metal lathe|lathe]] or [[Milling (machining)|mill]], a [[cutting tool (machining)|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<ref>Karlo Apro (2008). ''[https://books.google.com/books?id=Ws228Aht0bcC Secrets of 5-Axis Machining]''. 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 [[Forming (metalworking)|forming]] or [[Burnishing (metal)|burnishing]] tools, [[Gerber format|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.<ref>{{cite book | last=Xu | first=Xun | date=2009 | url=https://www.google.com/books/edition/Integrating_Advanced_Computer_Aided_Desi/habcATPQWJ4C | title=Integrating Advanced Computer-aided Design, Manufacturing, and Numerical Control: Principles and Implementations | publisher=Information Science Reference | page=166 | isbn=9781599047164 | via=Google Books}}</ref><ref>{{cite book | last=Harik | first=Ramy | author2=Thorsten Wuest | date=2019 | url=https://www.google.com/books/edition/Introduction_to_Advanced_Manufacturing/O3h0EAAAQBAJ | title=Introduction to Advanced Manufacturing | publisher=SAE International | page=116 | isbn=9780768090963 | via=Google Books}}</ref> The first [[Technical standard|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).<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 | work=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 ''[[International Organization for Standardization|ISO]] 6983'' (finalized in 1982) is often used, but many European countries use other standards.<ref>{{cite book | last=Stark | first=J. | author2=V. K. Nguyen | date=2009 | url=https://www.google.com/books/edition/Advanced_Design_and_Manufacturing_Based/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=9781848827394 | via=Google Books}}</ref> For example, ''[[Deutsches Institut für Normung|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 are not as troublesome because machining operations are usually developed with CAD/CAM applications that can output 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 language|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,<ref>{{cite web |url-status=dead |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.▼
== 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.<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=9781483292489|___location=Burlington|pages=321|oclc=895436474}}</ref>
▲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 are not as troublesome because machining operations are usually developed with CAD/CAM applications that can output the appropriate G-code for a specific machine through a software tool called a post-processor (sometimes shortened to just a "post").
Some CNC machines use "conversational" programming, which is a [[wizard (software)|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.
▲G-code began as a limited language that lacked constructs such as loops, conditional operators, and programmer-declared variables with [[Natural language|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,<ref>{{cite web |url-status=dead |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.
== See also ==
{{too many see alsos}}
* [[3D printing]]
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* [[Coordinate system]]
* [[Cutter ___location]]
* [[Direct Numerical Control]]
* [[Drill file (disambiguation)]]
* [[Gerber file]]
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