Chapter 4 cnc part programming

Chapter 4
CNC Part Programming
Prepared by: Prof. Rahul Thaker (ACET)

Reference systems
 M - Machine Zero or home: This is set by the
manufacturer as the origin of the coordinate system of the
machine.

Reference systems
W - Part zero or point of origin of the part: This is the
origin point that is set for programming the measurements of
the part. It can be freely selected by the programmer.
 R - Machine Reference point : This is a point on the
machine established by the manufacturer around which the
synchronization of the system is done. The control positions
the axis on this point.

CNC PROGRAMMING
CNC is the part program is a set of encoding information,
giving co-ordinates and other details to indicate how a tool
should move in a relation to a work piece in a machine
should perform desirable operation on the job. CNC controls
will be the program and execute the operations. The program
is prepared by co-ordinate values (XYZ) of the entire tool
path as suited to machine to complete the component and it
also contains the following basic information.
•Preparatory function (G code)
•Miscellaneous function (M code)
•Spindle speed (S)
•Feed rate (F)
•Tool number (T)

Programming Key Letters
O - Program number (Used for program identification)
N - Sequence number (Used for line identification)
G - Preparatory function
X - X axis designation
Y - Y axis designation
Z - Z axis designation
R - Radius designation
F – Feed rate designation
S - Spindle speed designation
H - Tool length offset designation
D - Tool radius offset designation
T - Tool Designation
M - Miscellaneous function

Word Address 1
N – Sequence or line number
• A tag that identifies the beginning of a block of
code. It is used by operators to locate specific lines of a
program when entering data or verifying the program
operation.
G – Preparatory function
• G words specify the mode in which the milling
machine is to move along its programmed axes.

Word Address 2
• Dimension Words
X – Distance or position in X direction
Y – Distance or position in Y direction
Z – Distance or position in Z direction
• M – Miscellaneous functions
• M words specify CNC machine functions not
related to dimensions or axial movements.

Word Address 3
• F – Feed rate (inches per minute or millimeters per
minute)
The feed function F is the speed at which the tool center
point moves.
The programmed F is effective working in linear (G01) or
circular (G02, G03).
The maximum F value is limited by the machine parameters.
Rate at which cutting tool moves along an axis.
• S – Spindle speed (rpm – revolutions per minute)
Controls spindle rotation speed.
• T – Tool number
Specifies tool to be selected.Prepared by: Prof. Rahul Thaker (ACET)

Word Address 4
• I – Circular cutting reference for x axis
• J – Circular cutting reference for y axis
• K – Circular cutting reference for z axis

G Word
• G words or codes tell the machine to perform
certain functions. Most G words are modal
which means they remain in effect until
replaced by another modal G code.

Common G Codes
• G00 – Rapid positioning mode
• Tool is moved along the shortest route to
programmed X,Y,Z position. Usually NOT used
for cutting.
• G01 – Linear Interpolation mode
• Tool is moved along a straight-line path at
programmed rate of speed.
• G02 – Circular motion clockwise (cw)
• G03 – Circular motion counter clockwise (ccw)

Common G Codes, con.,
• G17 – XY plane
• G18 – XZ plane
• G19 – YZ plane
• G20 – Inch Mode
• G21 – Metric Mode
• G28 – Return to axis machine Zero (Home)

G Codes: G90, G91
G90 – Absolute Coordinate Reference
References the next position from an absolute zero
point which is set once for the entire program.
G91 – Incremental Coordinate Reference
References the next position from the previous
position.

G Codes: Cutter Compensation
• G40 – Cancel cutter diameter compensation.
• G41 – Cutter compensation left.
• G42 – Cutter compensation right.

M Word
• M words tell the machine to perform certain
machine related functions, such as: turn
spindle on/off, coolant on/off, or stop/end
program.
Professional Development ID Code: 6006

Common M words
• M00 – Programmed pause
• Automatically stops machine until operator pushes a button
to resume program.
• M01 – Optional stop
• A stop acted upon by the machine when operator has
signaled this command by pushing a button.
• M02 – End of program
• Stops program when all lines of code are completed. Must
be last command in program.

Common M words
• M03 – Turn spindle on
• In clockwise direction
• M04 – Turn spindle on
• In counter clockwise direction
• M05 – Stop spindle
• Usually used prior to tool change or at end of program.
• M06 – Tool change
• Stops program and calls for a tool change, either
automatically or manually.

Common M words
• M08 – Turns Accessory 1 on.
• M09 – Turns Accessory 1 off.
• M10 – Turns Accessory 2 on.
• M11 – Turns Accessory 2 off.
• M30 – End of program
• Similar to M02 but M30 will also “rewind” the
program. Must be last statement in program. If used, DO
NOT use M02.

N02 G21 Metric programming
N03 M03 S1000 Spindle start clockwise with 1000rpm
N04 G00 X0 Y0 Rapid motion towards (0,0)
N05 G00 Z-10.0 Rapid motion towards Z=-10 plane
N06 G01 X50.0 Linear interpolation
N07 G01 Y20.0 Linear interpolation
N08 G02 X25.0
Y45.0 R25.0 Circular interpolation clockwise(cw)
N09 G03 X-25.0
Y45.0 R25.0 Circular interpolation counter clockwise(ccw)
N10 G02 X-50.0
Y20.0 R25.0 Circular interpolation clockwise(cw)
N11 G01 Y0.0 Linear interpolation
N12 G01 X0.0 Linear interpolation
N13 G00 Z10.0 Rapid motion towards Z=10 plane
N14 M05 M09 Spindle stop and program end
EXAMPLE

N01 G91 G71 M03 S800 (incremental mode,metric, spindle start with a speed of 800 rpm)
N02 G00 X1.0 (tool away from work piece 1mm, rapid)
N03 G00 Z-1.0 (tool to left 1mm for facing)
N04 G01 X-16.0 F200 (facing cut at a feed rate 200mm/min)
N05 G00 Z1.0 (move tool to right 1mm from that position)
N06 G00 X10.0 (move 10 mm away from the centre in x direction)
N07G01 Z-36.0 (plane turning over a length of 35 mm)
N08 G01 X5.0 Z-30.0 (simultaneous movement in X and Z directions for taper turning)
N09 G00 X1.0 Z66.0 (move to the starting position)
N10 M02 (end of program) Prepared by: Prof. Rahul Thaker (ACET)

N01 G90 G71 M03 S800 (absolute, metric, start spindle at a speed 800 rpm)
N02 G00 X0.0 Y0.0 (move tool to the beginning of cut)
N03 G02 X10.0 Z-10.0 I 0.0 K-10.0 F150 (clockwise circular interpolation, I&K are
offsets, feed rate 150mm/min)
N04 G00 Z-30.0 (move from point B to point C)
N05 G03 X15.0 Z-35.0 I5.0 K0.0 (counterclockwise interpolation, I&K are
offsets, move to point D)
N06 M02 (end of program)

Subroutines
 Any frequently programmed order of instruction or
unchanging sequences can benefit by becoming a subprogram.
Typical applications for subprogram applications in CNC
programming are :
• Repetitive machining motions
• Functions relating to tool change
• Hole patterns
• Grooves and threads
• Machine warm-up routines
• Pallet changing
• Special functions and others

Subroutines
 Structurally, subprograms are similar to standard programs. They use the same
syntax rules. The benefits of subroutines involve the reduction in length of
program, and reduction in program errors. There is a definition statement and
subroutine call function.
Standard sub-routine
N10
N20
N30
….
N70 G22 N5
N80
N90
….
N100 G24
….
N160 G20 N5
 In the above example G22 statement defines the start block of the sub-routine and G24
marks the end of the sub-routine statement. The subroutine is called by another code
G20 identified by the label N5.Prepared by: Prof. Rahul Thaker (ACET)

Canned Cycles
A canned cycle is a preprogrammed sequence of events
/ motions of tool / spindle stored in memory of
controller. Every canned cycle has a format. Canned
cycle is modal in nature and remains activated until
cancelled. Canned cycles are a great resource to make
manual programming easier. Often underutilized,
canned cycles save time and effort.

Chapter 4 cnc part programming

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Chapter 4 cnc part programming