Introduction to G-CODES used in CNC Programming
A G-code is defined using the G address letter and a two
digit number in NC Programming, example: G00
G-Code is mostly used common name in NC Programming language
since they prepare the machine for a certain type of motion. G-codes instruct
the machine where to move, how fast to move and which path to move. G-codes are
called as Preparatory codes which prepare machine to move.
There are two types of G-codes,
1)
Modal G-code.
2)
Non-Modal
G-code.
1). Modal G-code: the G-codes for motions are called Modal
G-code. The modal G-code once called it stays till it is cancelled with another
G-code. If G1 (Linear Move) command is
called it will be executed again on the next line unless some other command called
which cancels G1.
Additionally, modal G codes are further split into groups
according to their task and function. A modal G code will remain active until
another G code from the same group is programmed into a block, or it is
cancelled. Example units of programming inches (G21) and millimetres (G20) are
modal. Model groups are as shown below.
Group 1
|
{G0,
G1, G2, G3, G80, G81, G82, G83, G84, G85, G86, G87, G88, G89} - motion
|
Group 2
|
{G17,
G18, G19} - plane selection
|
Group 3
|
{G90,
G91} - distance mode
|
Group 5
|
{G93,
G94} - spindle speed mode
|
Group 6
|
{G20,
G21} - units
|
Group 7
|
{G40,
G41, G42} - cutter diameter compensation
|
Group 8
|
{G43,
G49} - tool length offset
|
Group 10
|
{G98,
G99} - return mode in canned cycles
|
Group 12
|
{G54,
G55, G56, G57, G58, G59, G59.1, G59.2, G59.3} coordinate system selection
|
2). Non-Modal G-codes: The Non-Modal G-codes effect only the
lines on which they occur. Example: G04 (Dwell) is Non-Modal. The machine
suspends machine motions code, dwells for the programmed time, and then returns
to normal movements.