Cnc Letter Addresses

Front 1

A

Back 1

Absolute or incremental position of A axis (rotational axis around X axis).

Front 2

B

Back 2

Absolute or incremental position of B axis (rotational axis around Y axis).

Front 3

C

Back 3

Absolute or incremental position of C axis (rotational axis around Z axis).

Front 4

D

Back 4

Defines diameter or radial offset used for cutter compensation. D is used for depth of cut on lathes.

Front 5

E

Back 5

Precision feed rate for threading on lathes.

Front 6

F

Back 6

Defines feed rate.

Common units are distance per time for mills (inches per minute, IPM, or millimeters per minute, mm/min) and distance per revolution for lathes (inches per revolution, IPR, or millimeters per revolution, mm/rev).

Front 7

G

Back 7

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.

Front 8

H

Back 8

Defines tool length offset; Incremental axis corresponding to C axis (e.g., on a turn-mill).

Front 9

I

Back 9

Defines arc center in X axis for G02 or G03 arc commands.

Front 10

J

Back 10

Defines arc center in Y axis for G02 or G03 arc commands.

Front 11

K

Back 11

Defines arc center in Z axis for G02 or G03 arc commands.

Front 12

L

Back 12

Fixed cycle loop count; Specification of what register to edit using G10.

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 K address is used instead of L. With incremental positioning (G91), a series of equally spaced holes can be programmed as a loop rather than as individual positions. G10 use: Specification of what register to edit (work offsets, tool radius offsets, tool length offsets, etc.).

Front 13

M

Back 13

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.

Front 14

N

Back 14

Line (block) number in program; System parameter number to be changed using G10.

Line (block) numbers: Optional, so often omitted. Necessary for certain tasks, such as M99 P address (to tell the control which block of the program to return to if not the default one) or GoTo statements (if the control supports those). N 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. System parameter number: G10 allows changing of system parameters under program control.

Front 15

O

Back 15

Program name

Front 16

P

Back 16

Serves as parameter address for various G and M codes.

With G04, 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 M98, it specifies which subprogram to call; with M99, it specifies which block number of the main program to return to.)

Front 17

Q

Back 17

Peck increment in canned cycles. For example, G73, G83 (peck drilling cycles)

Front 18

R

Back 18

Defines size of arc radius, or defines retract height in milling canned cycles.

For radii, not all controls support the R address for G02 and G03, in which case IJK vectors are used. For retract height, the "R level", as it's called, is returned to if G99 is programmed.

Front 19

S

Back 19

Defines speed, either spindle speed or surface speed depending on mode.

Data type = integer. In G97 mode (which is usually the default), an integer after S is interpreted as a number of rev/min (rpm).

In G96 mode (CSS), an integer after S is interpreted as surface speed—sfm (G20) or m/min (G21).

On multifunction (turn-mill or mill-turn) machines, which spindle gets the input (main spindle or subspindles) is determined by other M codes.

Front 20

T

Back 20

Tool selection.

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. Programming on any particular machine tool requires knowing which method that machine uses

Front 21

U

Back 21

Incremental axis corresponding to X axis (typically only lathe group A controls).

Also defines dwell time on some machines (instead of "P" or "X").

In these controls, X and U obviate G90 and G91, respectively. On these lathes, G90 is instead a fixed cycle address for roughing.

Front 22

V

Back 22

Incremental axis corresponding to Y axis.

Front 23

W

Back 23

Incremental axis corresponding to Z axis (typically only lathe group A controls).

Front 24

X

Back 24

Absolute or incremental position of X axis.

Front 25

Y

Back 25

Absolute or incremental position of Y axis.

Front 26

Z

Back 26

Absolute or incremental position of Z axis.