CNC Letters NOTE: The following will be a listing and description of Computer Numerical Control (CNC) Codes and Letter designations. We will try to stick with only “generic” codes that will work on most machines. Some examples may be specifically for the machines we have at South Adams / Area 18 Machine Trades. Please contact the instructor if you find any errors, missing items, or anything you would like to see added. jdailey@southadams.k12.in.us

You should already have a list of G&M Codes and CNC Letters as shown. If you do not have one, see your instructor, or download one off of the South Adams / Area 18 Machine Trades

Letter Meaning

A Rotary indexing axis around the "X" axis

B Rotary indexing axis around the "Y" axis

C Rotary indexing axis around the "Z" axis

D Cutter Radius / Diameter offset number

E Feedrate in inches per revolution (Lathe)

F Feedrate in inches per minute (can be used on lathes)

G Preparatory commands

H Offset Number (Mill - tool length)(Lathe - Position offset)

I Arc center location in the "X" axis

J Arc center location in the "Y" axis

K Arc center location in the "Z" axis

L Fixed Cycle repetition count / subprogram repetition count

M Miscellaneous function

N Block / Sequence number

O Program Number

P Subprogram / Macro Number call

P Dwell time in milliseconds

P Block number in main program when used with M99

Q Depth of peck in fixed cycles (G73and G83)

Q Shift amount in fixed cycle (G76 and G87)

R Retract point in fixed cycles

R Arc Radius designation

S Spindle speed in RPMs

T Tool function

U Incremental move in "X" axis

V Incremental move in "Y" axis

W Incremental move in "Z" axis

X "X" axis coordinate value designation

Y "Y" axis coordinate value designation

Z "Z" axis coordinate value designation

CNC Alphabet- We learned our A-B-C’s at home with our

parents, in pre-school or kindergarten but I bet you never knew they could be this powerful.

- Most of what we are going to start with will be based around a Fanuc 3 Axis CNC Vertical Milling Machine

X – Y – Z We are going to start with the end of the alphabet first since you have been using the Cartesian coordinate system in math class for several yearsZ = The axis that is parallel to the spindleX = The axis which is normally the longest Linear movement that crosses the “Z” axisY = The last axis on a 3-axis machine, normally the shorter linear movement that crosses the “Z” axis and is perpendicular to “X” axis

A-B-C- A, B, C axes are used when you want to rotate or

index the part

- A = The Rotary axis around the X axis- B = The Rotary axis around the Y axis- C = The Rotary axis around the Z axis

X Y ZA B C

X-

Z-

Z+

X+

Y+/-

A

C

B

D- Cutter Diameter Compensation Number

- Some machines may require the Radius of the tool- The Number associated with the “D” refers to

where in the “Offsets” page the program will look to find the right number to use.

Example: G41 D14

E- Feedrate on a CNC Lathe

- Specified as IPR (Inches Per Revolution)

Example: G01 X1.0 E.006

F- Feedrate on a CNC Mill or Lathe

- Milling = Specified as IPM (Inches Per Minute)- Lathe = Specified as IPR (Inches Per Revolution)

Example: Mill = G01 X1.0 F12.0 (12 IPM)Lathe = G01 X1.0 F0.006 (.006 IPR)

G- Preparatory Commands

- The “G” codes typically prepare or prompt the machine to do something

- Preparatory Definition (according to www.dictionary.com)

1. Serving or designed to prepare2. Preliminary; Introductory

Example: G17 G20 G40 G80 G90

H- Height Offset- Cutter Compensation typically used to

compensate for the Length of the tool - G43 or G44

- Typically the distance the tool would need to travel to get from the “Z” home position to the top of the part

- The Number associated with the “H” refers to where in the “Offsets” page the program will look to find the right number to use.

Example: G43 H14

I-J-K- I, J, K axis are used when you need to specify the

point from where the tool is currently at to the centerline of the arc when using G02 or G03

- I = Radius centerline location on the X axis- J = Radius centerline location on the Y axis- K = Radius centerline location on the Zaxis

X Y ZI J K

L1. Canned or Fixed Cycle Repetition Count

- Example: 10 holes 1” apart, .250 deep- G81 X1.0 Y2.0 Z-.250 R.100- G91 X1.0 L9

2. Sub-Program Repetition Count- Example: Call up Program o1001 and repeat 10 times

- M98 P1001 L10

M1. Miscellaneous Functions

- Typically turns something ON or OFF- M30 = turns OFF program- M03 = turns ON spindle- M05 = turns OFF spindle- M98 = turns ON a sub-program- M99 = turns OFF a sub program- M07 = turns ON mist coolant- M09 = turns OFF coolant

N- Line Number

- Typically by Ten’s- Example:

- N0010- N0020- N0030- N0040

- Reason it is by Ten’s…..- What if you had a 3000 line program and realized you

forgot something between line N0030 and N0040…- Answer: You could number lines N0031, N0032, N0033,

N0034, N0035, N0036, N0037, N0038, N0039- You do not have to renumber the whole program! (but you can)

O- Program Number

- On most older machines it must be:- the letter O and any four digits

- No more… no less

- Nowadays, most machines will take about anything as a program name

- Most program numbers would benefit by being the same number as the part number

P1. Sub-Program call number – when used with M98

- Used in the place of “O”

2. Work Offset Number – when used with G10

3. Dwell time in milliseconds: G4 and Canned cycles- to renumber the whole program! (but you can)

4. Block Number in main program - When used with M99

Q1. Depth of peck in Canned or Fixed Cycles

- G73 or G83- G83 X2.0 Y3.0 Z-1.50 R.100 Q.250 F6.0

2. Shift amount in Canned or Fixed Cycles- G76 or G87

R1. Retract point in Canned or Fixed Cycles

- G83 X2.0 Y3.0 Z-1.50 R.100 Q.250 F6.0

2. Arc Radius Designation- G02 X1.0 Y1.0 R1.0

S- Spindle Speed in RPMs

- M03 S1500

T- Tool Function

- Specifies what tool number you want to use- M06 T10

U-V-W- U, V, W axes are used when you an auxiliary axis

parallel to the XYZ axes- Incremental move parallel to the XYZ axes

- U = Incremental move in the “X” axis- V = Incremental move in the “Y” axis- W = Incremental move in the “Z” axis

X Y ZU V W

X-Y-Z- X, Y, and Z are probably the 3 most popular

letters in CNC Programming even though they are last!

- Don’t forget, there are a lot of other letters that are directly related to the XYZ axes X Y Z

A B CI J KU V W