cnc machining

ME 3480 CNC Machining (Self-Study)
Basic components of CNC machining system- Machine Control Unit, Part
Programming methods, machine tools, automatic tool changing systems,
automatic work holding systems, interpolators ( Mid sem portion)
Sequential controllers-manual part programming and machining of rotational
and prismatic components with two and three axes MNC machine tools- Tools
presetting and work setting procedures- Computer assisted part programming-
Complex surface machining- Tool path generation for rough and finish
machining of complex surfaces- Quality aspects in CNC machining of
different surfaces.
References:
1. Yoram Koren, Computer control of manufacturing systems, McGraw Hill,
New York 1983
2. James Madison, CNC Machining Handbook, Industrial Press, New York,
1996.

Numerical Control (NC) Defined
Programmable automation in which the mechanical actions of a ‘machine
tool’ are controlled by a program containing coded alphanumeric data
that represents relative positions between a work head (e.g., cutting
tool) and a work part
Machine
Control Unit
Power
Program
Instructions
Transformation
Process

NC Coordinate Systems
For flat and prismatic (block-like) parts:
• Milling and drilling operations
• Conventional Cartesian coordinate system
• Rotational axes about each linear axis
For rotational parts:
• Turning operations
• Only x- and z-axes

Motion Control Systems
Point-to-Point systems
• Also called position systems
• System moves to a location and performs an
operation at that location (e.g., drilling)
• Also applicable in robotics
Continuous path systems
• Also called contouring systems in machining
• System performs an operation during movement
(e.g., milling and turning)

Interpolation Methods
1. Linear interpolation
– Straight line between two points in
space
2. Circular interpolation
– Circular arc defined by starting point,
end point, center or radius, and
direction
3. Helical interpolation
– Circular plus linear motion
4. Parabolic and cubic interpolation
– Free form curves using higher order
equations

Absolute vs. Incremental Positioning
Absolute positioning
Move is: x = 40, y = 50
Incremental positioning
Move is: x = 20, y = 30.

• Computer Numerical Control machining is a
subtractive method
• Mostly 5 axes of control at most, 3 axes of
control
• Tolerance limits are determined by accuracy of
x-y tables
• CNC has the highest relative tolerances of any
manufacturing method
CNC Overview

Computer Numerical Control
• Numerical control is a method of automatically
operating a manufacturing machine based on a code
of letters, numbers, and special characters.
• The numerical data required to produce a part is
provided to a machine in the form of a program,
called part program or CNC program.
• The program is translated into the appropriate
electrical signals for input to motors that run the
machine.

 Increase production throughput
 Improve the quality and accuracy of manufactured
parts
 Stabilize manufacturing costs
 Manufacture complex or otherwise impossible jobs -
2D and 3D contours
Why Use CNC Machines?

Advantages of CNC
• Flexibility of operation is improved, as is the ability to
• Produce complex shapes with good dimensional accuracy,
• Repeatability, reduced scrap loss, and high production
rates,
• Tooling costs are reduced, since templates and other
fixtures are not required.
• Machine adjustments are easy to make with
microcomputers
• More operations can be performed with each setup, and
less
• lead time for setup and machining is required compared to
• conventional methods. Design changes are facilitated, and
• inventory is reduced.

Computer Numerical Control (CNC)
• Storage of more than one part program
• Various forms of program input
• Program editing at the machine tool
• Fixed cycles and programming subroutines
• Interpolation
• Acceleration and deceleration computations
• Communications interface
• Diagnostics

DNC
• Direct numerical control (DNC) – control of multiple
machine tools by a single (mainframe) computer
through direct connection and in real time
– 1960s technology
– Two way communication
• Distributed numerical control (DNC) – network
consisting of central computer connected to machine
tool MCUs, which are CNC
– Present technology
– Two way communication

Distributed Numerical Control
Machine
Control Unit
Transformatio
n
Process
Machine
Control Unit
Machine
Control Unit
Central
Computer NC Pgms
BTR BTR BTR
Computer Network

Cost-Benefits of NC
Costs
• High investment cost
• High maintenance effort
• Need for skilled programmers
• High utilization required
Benefits
• Cycle time reduction
• Nonproductive time reduction
• Greater accuracy and repeatability
• Lower scrap rates
• Reduced parts inventory and floor space
• Operator skill-level reduced

CNCs comprises: CNC unit，
feed motion servo subsystem，
spindle servo subsystem
and some auxiliary control cells.
Operation panel
I/O Devices
CNC
Control Unit
PLC
Keyboard
Spindle servo cell
Machine tool I/O circuits and devices
Spindle driver
Feed motion
servo cells
Detect device
Feed drivers
Machine
tool

Functions and features of CNC
Controlling function
Number of control axes and synchronously control axes:
linear axes and rotate axes, basic axes and auxiliary
axes.(The more the number of controlled axes，especially
the number of axes being controlled synchronously，the
more powerful functions of the CNC unit, and the more
complex structure of the CNC unit，the more difficulty of
programming.)
Preparatory function
G function, describes the motion modes of CNC machine
The motion modes comprise instructions of basic motionsdwell plane
selections, coordinate system settings，tool compensations，
reference point return fixed operation circles，and metric/inch unit
transfer，etc．

Interpolation function
interpolation by using software real-time calculations．
Linear interpolation，circular interpolation，helical interpolation，
and polar coordinate interpolation
Feed function
Feed rate designation
(machining centers only allow the feed rate to be specific in per-minute
format: inches or millimeters per minute;
Turning centers，which have position encoders in their spindles，also
allow feed rate to be specified in per-revolution format: inches or
millimeters per revolution)
Feed Rate Override: multiple position switch on control panel
allows the operator to change the programmed feed rate during cutting
(The switch is usually segmented in 10 percent increments
that range from 0 percent through 200 percent )
Functions and features of CNC

Rapid motion
to minimize non-productive time during the machining cycle
↑
to command motion at the machine’s fastest possible rate．
• Common uses for rapid motion: non-cutting motion
| include :
positioning the tool to and from cutting positions，
moving to clear clamps and other obstructions

Spindle function
specify the spindle speed
On operation panel，there is a button to turn the spindle
on and off，as well as a rheostat to control spindle
speed．
Miscellaneous function
allow a variety of special functions
Miscellaneous functions are typically used as
programmable switches
∣
(spindle on/off，coolant on/off，and so on)

Compensation function
allow the CNC user to
allow for unpredictable conditions related to tooling
Tool length compensation，cutter radius compensation，
and tool nose radius compensation→
enable the CNC machine to adjust cutting tool to zero in the right
position
when wear occurs on cutter tool or changing of cutting tool
Technical parameters compensation,
( fixture offset，
NRZ(Non-return-to-Zero) of axis while counter-moving，
distortion of machine tool
any unpredictable situations during programming
∣
a form of compensation to deal with the problem

Enhanced function
graphic display function
CRT or LCD displayer: show programs，parameters，various
compensation data，coordinates，
fault information，
part graphs;
monitor dynamic cutter tool paths while
machining
Self-diagnosis function
various diagnosis programs : prevent faults occurring
or going worse
to shorten the time of broken-down
Communication function
RS-232-C communications (serial) port←→ personal computers
Some form of communications software →allow transmissions

Programming function
Manual programming，
all CNC programmers should have a good understanding of
manual programming techniques regardless of whether or
not they are used．
conversational (shop-floor) programming，
created using graphic and menu-driven functions
visual check
and CAM system programming
helps the programmer in three major areas：
keeps the programmer from having to do math calculations，
makes easy to program different kinds of machines with
the same basic language，
helps with certain basic machining practice functions

Functional interface
between hardware and software in CNC unit
CNC unit : hardware + software
↓
work together to perform all functions of CNC unit
different characters:
Hardware→ higher speed ，more expensive；
software → flexible ，slow on processing
→
proportion between hardware and software is determined
by cost-performance of the CNC unit
(In the earlier NC equipments，all functions were implemented by hardware;
computer was introduced into CNC system)
↓
participations of computer different in different CNC units
in different time

four different functional interfaces between hardware and
software:
Program
Input
Interpolation
Position
Pretreatment
Speedcontrol
Servomotor
Detector
Hardware
Software Hardware
Hardware
Hardware
Software
Software
1
2
3
4 Software Hardware

Holononic CNC lath system of this architecture
modules can be connected together by industry standard bus: IPC (Industry PC) bus or STD
bus

Open Loop vs. Closed Loop controls

Components of Servo-motor controlled CNC
Motor speed control
Two types of encoder configurations
Motor lead screw rotation table moves
position sensed by encoderfeedback

Motion Control and feedback
Encoder outputs: electrical pulses (e.g. 500 pulses per revolution)
Rotation of the motor  linear motion of the table: by the leadscrew
The pitch of the leadscrew: horizontal distance between successive threads
One thread in a screw  single start screw: Dist moved in 1 rev = pitch
Two threads in screw  double start screw: Dist moved in 1 rev = 2* pitch

Example 1
A Stepping motor of 20 steps per revolution moves a machine table through
a leadscrew of 0.2 mm pitch.
(a) What is the BLU of the system ?
(b) If the motor receives 2000 pulses per minute, what is the linear
velocity in inch/min ?

Example 2
A DC servo-motor is coupled to a leadscrew (pitch 5mm) of a machine table. A digital
encoder, which emits 500 pulses per revolution, is mounted on the leadscrew. If the
motor rotates at 600 rpm, find
(a) The linear velocity of the table
(b) The BLU of the machine
(c) The frequency of pulses emitted by the encoder.

Types of CNC machines
Based on Motion Type:
Point-to-Point or Continuous path
Based on Control Loops:
Open loop or Closed loop
Based on Power Supply:
Electric or Hydraulic or Pneumatic
Based on Positioning System
Incremental or Absolute

Source : Dr.Dimiritis moutrzis

CNC WORK HOLDING DEVICES
With the advent of CNC technology, machining cycle times were drastically
reduced and the desire to combine greater accuracy with higher productivity has
led to the reappraisal of work holding technology. Loading or unloading of the
work will be the non-productive time which needs to be minimized. So the work is
usually loaded on a special work holder away from the machine and then
transferred it to the machine table. The work should be located precisely and
secured properly and should be well supported.
Turning center work holding methods
Machining operations on turning centers or CNC lathes are carried out mostly
for axi-symmetrical components. Surfaces are generated by the simultaneous
motions of X and Z axes. For any work holding device used on a turning centre
there is a direct "trade off" between part accuracy and the flexibility of work
holding device used.

Work holding methods Advantages Disadvantages
Automatic Jaw &
chuck changing
Adaptable for a range of work-piece
shapes and sizes
High cost of jaw/chuck changing automation.
Resulting in a more complex & higher cost
machine tool
Indexing chucks
Figure 28.1
Very quick loading and unloading of
the workpiece can be achieved.
Reasonable range of work piece
sizes can be loaded automatically
Expensive optional equipment. Bar-feeders
cannot be incorporated. Short/medium
length parts only can be incorporated. Heavy
chucks.
Pneumatic/Magnetic
chucks
Figure 28.3
Simple in design and relatively
inexpensive. Part automation is
possible. No part distortion is caused
due to clamping force
Limited to a range of flat parts with little
overhang. Bar-feeders cannot be
incorporated. Parts on magnetic chucks
must be ferrous. Heavy cuts must be
avoided.
Automatic Chucks with
soft jaws
Adaptable to automation. Heavy cuts
can be taken. Individual parts can be
small or large in diameter
Jaws must be changed manually & bared, so
slow part change-overs. A range of jaw
blanks required.
Expanding mandrels &
collets
Figure 28.2
Long & short parts of reasonably
large size accommodated.
Automation can be incorporated.
Clamping forces do not distort part.
Simple in design
Limitation on part shape. Heavy cuts should
be avoided.
Dedicated Chucks
Excellent restraint & location of a
wide range of individual & irregular -
shaped parts can be obtained.
Expensive & can only be financially justified
with either large runs or when extremely
complex & accurate parts are required. Tool
making facilities required. Large storage
space.
WORK HOLDING DEVICES

WORK HOLDING DEVICES FOR
MACHINING CENTER

VISE
Magnetic chucks
Indexing chucks
Pallets
Mandrels
WORK HOLDING DEVICES

Work holding methods Advantages Disadvantages
Modular Fixtures
Highly adaptable. Can be purchased in
stages to increase its sophistication.
Reasonable accuracy. Speedily
assembled. Small stores area is required.
Can be set-up to a machine more than
one part. Proven technology
Costly for a complete system. Difficult to
automate. Skills required in kit assembly
Automatic Vices
Relatively inexpensive. Can be operated
by mechanical, pneumatic, or by
hydraulic control. Quick to operate with
ease of set-up. Reasonable accuracy.
Easily automated. Simplicity of design.
Using multi-vices allows many parts to be
machined. Proven Technology
Work holding limitations. Clamping force
limitations. Jaws can become strained.
Work location problems. Limitations on
part size.
Pneumatic/Magnetic Work holding
devices
Relatively inexpensive. Reasonable
accuracy. Can machine large areas of the
work piece. Quick setups. Easily
automated. Simplicity of design. Many
parts can be machined at one set up.
Large surface area is required. Swarf can
be a problem. Nonferrous material
limitation on magnetic devices.
4/5 axis CNC work holding devices
Allows complex geometric shapes to be
machined. High accuracy. Opportunity for
"one hit" machining. Easily automated.
Costly & limited part geometry clamping.
Part size limitations. Usually only one
part can be machined. Cannot be fitted to
all machines.
Dedicated Fixturing
Large & small parts are easily
accommodated. High accuracy of part
location. Easily automated. Simplicity of
design. Proven technology. Many parts
can be machine at one setup good
vibration damping capacity
Large storage space required. No part
flexibility. Heavy fixtures. Tool making
facilities required.
Work holding devices for Machining center

• Program
– A program is a set of instructions or commands
given to a computer.
• Part program
– A program that is used for machining a part.
– Program consists of
• Dimensional data - the size and shape of the
component
• Technological data – Sequence of operations, Cutting
speed, feed rate etc.
• Miscellaneous data – Coolant ON / OFF, Spindle ON /
OFF, Tool CLAMP /UNCLAMP etc.
Part Programming

Axis and Motion Nomenclature
Machine coordinate system?
• The direction of each finger
represents the positive direction of
motion.
• The axis of the main spindle is
always Z, and the positive direction
is into the spindle.
• On a mill the longest travel
slide is designated the X axis and is
always perpendicular to the Z axis.
• If you rotate your hand looking
into your middle finger, the
forefinger represents the Y axis.
• The base of your fingers is
the start point or (X0, Y0, Z0).

Rotary Motion
• The right-hand rule for
determining the correct axis on a CNC
machine may also be used to determine
the clockwise rotary motion about X, Y,
and Z.
• To determine the positive, or
clockwise, direction about an axis, close
your hand with the thumb pointing out.
- The thumb may represent the X, Y,
or Z direction and the curl of the fingers
may represent the clockwise, or positive,
rotation about each axis.
- These are known as A, B, and C
and represent the rotary motions about X,
Y, and Z, respectively.

1. CNC Mill
2. Vertical CNC Knee
Mill
3. CNC Lathe
4. Five Axis CNC
contour Mill

CNC Milling Fundamentals
Three Cartesian Planes
• The three planes in the Cartesian coordinate system are XY,
XZ, and YZ.
• These are referred to as G17, G18, and G19, respectively, on
the mill.

The Part Reference Zero (PRZ)
• There are two reference points on a CNC
Machine: Machine Reference Zero (MRZ) and the
Part Reference Zero (PRZ). All coordinates are
based on these two points.
- All CNC machine tools require a reference
point from which to base coordinates.
- It is generally easier to use a point on the
workpiece itself for reference, because the
coordinates apply to the part anyway – thus the
PRZ designation
- The PRZ is defined as the lower left-hand
corner and the top of the stock of each part

The Part Reference Zero (PRZ)
• The advantages of having the PRZ at the lower left top
corner are:
- Geometry creation is in the positive XY plane for
CAD/CAM systems
- The corner of the workpiece is easy to find.
- All negative Z depths are below the surface of the
workpiece.

The Cartesian Graph
• Cartesian coordinates
were invented by René
Descartes, who is famous for
the phrase "I think, therefore
I am."
• Most Cartesian graphs
for milling and turning use a
three-axis coordinate
system, denoted by the X, Y,
and Z axes.
• These coordinates are
used to instruct the machine
tool where to move on the
workpiece

Absolute Coordinates
• Absolute coordinates
use the origin as the
reference point.
• This means that any
point on the Cartesian
graph can be plotted
accurately by measuring
the distance from the origin
to the point
• First in the X direction,
then in the Y direction, and
then, if applicable, in the Z
direction.

Incremental Coordinates
• Incremental coordinates use
the present position as the
reference point for the next
movement.
• This means that any point
in the Cartesian graph can be
plotted accurately by
measuring the distance between
points, generally starting at the
origin.

Cartesian Coordinates

CNC Milling
Fundamentals
Absolute Coordinates – Exercise 1
Fill in the X and Y blanks with the appropriate absolute
coordinates for
points A through H.

Incremental Coordinates – Exercise 2
Fill in the X and Y blanks with the appropriate incremental coordinates
for points A through H.

CNC Turning Fundamentals
Axis Coordinate System
• CNC lathes share the same two-axis coordinate
system.
• This allows for the transfer of CNC programs
among different machines, as all measurements are
derived from the same reference points.
• In CNC turning there is a primary, or horizontal, axis
and a
secondary, or vertical, axis. Because the major axis
always runs through the spindle(horizontally), the Z
axis is usually the longer one. The X axis is
perpendicular to the Z axis (or vertical).
• It is important to remember that on most CNC lathes
the
tool post is on the top, or backside, of the machine,
unlike on a conventional lathe.

Cartesian Graph for Turning
•When measuring X and Z
coordinates, use a central
reference point.
• Start all measurements at
this reference point, the
origin point (X0, Z0).
• For all our examples the
origin is located at the
center right-hand endpoint
of the workpiece.
• Keep in mind that at
times the center left-hand
endpoint of the workpiece
may be used

Diameter Programming
•Diameter (or diametrical)
programming relates the
X axis to the diameter of
the workpiece.
• For example, if the
workpiece has a 5-in
outside diameter and you
want to command an
absolute move to the
outside, you would
program
X5.0

Radial Programming
• Radius (or radial)
programming relates the
X axis to the radius of the
workpiece.
• For example, for the
same 5-in. outside
diameter workpiece, you
would program X2.5 to
move the tool to the
outside.

Absolute Coordinates
• When plotting points using
absolute coordinates, always
start at the origin
(X0, Z0).
• Then travel along the Z axis
until you reach a point directly
below the point that you are
trying to plot.
• Write down the Z value and
then go up until you reach
your point.
• Write down the X value.
You now have the XZ (or ZX)
coordinate for that point.

CNC Turning
Fundamentals
Incremental Coordinates
• The second method for
finding points in a
Cartesian coordinate
system is by using
incremental coordinates.
• Incremental, or relative,
coordinates use each
successive point to
measure the next
coordinate.
• Instead of constantly
referring back to the origin,
the incremental method
refers to the previous point

Incremental Coordinates – Exercise 3
Using Incremental Coordinates. Find the diametrical X and Z
coordinates for points A through E.

Absolute Coordinates – Exercise 4
Using Absolute Coordinates. Find the diametrical X and Z
coordinates for points A through E.

Letter Codes
• Each instruction to the
machine consists of a letter
followed by a number.
• Each letter is associated with
a
specific type of action or piece
of information needed by the
machine.
• Letters used in Codes
N,G,X,Y,Z,A,B,C,I,J,K,F,S,T,R
,M
CNC Program Codes

CNC Program Codes
Letter Codes – G Codes

Letter Codes – G & M Codes
• G-codes: Preparatory
Functions
– involve actual tool moves
• M-codes: Miscellaneous
Functions
– involve actions necessary
for machining (i.e. spindle
on/off, coolant on/off)
CNC Program Codes

Letter Codes – M Codes
CNC Program Codes

CNC Program Codes
Tool Motion Codes
• Generally, three types of tool motion are used on a CNC
machine:
G00 Rapid tool move. Non-machining command.
Each axis trajectory is exhausted as fast as the
motor can drive the axes.
G01 Straight-line feed move. Linear interpolation.
Coordinated moves at a controlled feedrate
G02/G03 Two-dimensional arc feed moves. Circular
interpolation.

Letter Codes – N Codes
• N-codes: Gives an identifying
number for each block of
information.
• It is generally good practice
to increment each block number
by 5 or 10 to allow additional
blocks to be inserted if future
changes are required.
CNC Program Codes

CNC Program Codes
Letter Codes – X Y & Z Codes
• X, Y, and Z codes are used to
specify the coordinate axis.
• Number following the code
defines the coordinate at the end
of the move relative to an
incremental or absolute reference
point.
• The number may require that
a specific format be used (i.e. 3.4
means three numbers before the
decimal and four numbers after
the decimal).

CNC Program Codes
Letter Codes – I J & K Codes
• I, J, and K Codes are used to
specify the coordinate axis when
defining the centre of a circle.
• Number following the code
defines the coordinate at the end
of the move relative to an
incremental or absolute reference
point.
• The number may require that a
specific format be used (i.e. 3.4
means three numbers before the
decimal and four numbers after
the decimal).

CNC Program Codes
Letter Codes – F S & T Codes
• F-Code: used to specify the
feedrate
• S-Code: used to specify the
spindle speed
• T-Code: used to specify the
tool identification number
associated with the tool to be
used in subsequent operations.

Letter Codes – R & P Codes
• R-Code:
- Retract distance when
used with G81, 82, and 83.
- Radius when used with
G02 and G03.
• P-Code: Used to specify
the dwell time associated
with G04.
CNC Program Codes

CNC Program Codes
Modal G Codes
• Most G Codes set the
machine in
a mode which stays in effect
until it is changed or
cancelled by another G Code
• These commands are called
modal
• In the example, G00 and
G01 are modal

CNC Program Codes
Modal G Codes

Format: N_ G02 X_ Y_ Z_ I_ J_ K_ F_ N_ G02 X_ Y_ Z_ R_ F_
G02 Circular Interpolation CW
•Circular Interpolation
is more commonly known
as radial (or arc) feed
moves.
• The G02 command
is specifically used for all
clockwise radial feed
moves, whether they are
quadratic arcs, partial
arcs, or complete circles,
as long as they lie in any
one plane.
• The G02 command
is modal and is subject to
a user-definable feed rate.
CNC Milling Programming

•The G02 command requires an
endpoint and a radius in order to
cut the arc.
• The start point of this arc is
(X1,Y4) and the endpoint is
(X4,Y1).
• To find the radius, simply
measure the incremental distance
from the start point to the center
point.
• This radius is written in
terms of the X and Y
distances.
• To avoid confusion, these
values are assigned variables,
called I and J, respectively.

EXAMPLE: G02 X2 Y1 I0 J-1
• The G02 command requires
an endpoint and a radius in order
to cut the arc.
(X1,
Y2) and the end-point is (X2,
Y1).
• To find the radius,
simply measure the relative, (or
incremental), distance from the
start point to the center point.
• This radius is written in terms
of the X and Y distances.
values are assigned variables

EXAMPLE: G02 X2 Y1 R1
• You can also specify G02 by entering the X and Y
endpoints and then R for the radius. Note: The use of
an R value for the radius of an arc is limited to a
maximum movement of
90°.
• To find I , calculate difference b/w arc start point
and center point in the X direction. In this case, both X
values are 1, so the I value is 0.
• To find J value, calculate difference b/w arc start
point and center point in Y direction. In this case, the
difference between Y2 and Y1 is down 1 inch, so the J
value is –1.

G02 Circular Interpolation Clockwise
Sample Program (G02):
Workpiece Size: X4, Y3, Z1
Tool: Tool #2, 1/4" Slot Drill
Tool Start Position: X0, Y0, Z1
%
:1003
N5 G90 G20
N10 M06 T2
N15 M03 S1200
N20 G00 X1 Y1
N25 Z0.1
N30 G01 Z-0.1 F5
N35 G02 X2 Y2 I1 J0 F20 (Arc feed CW, radius I1,J0 at 20 ipm)
N40 G01 X3.5
N45 G02 X3 Y0.5 R2 (Arc feed CW, radius 2) N50 X1 Y1 R2
(Arc feed CW, radius 2) N55 G00 Z0.1
N60 X2 Y1.5
N65 G01 Z-0.25
N70 G02 X2 Y1.5 I0.25 J-0.25 (Full circle arc feed move CW)
N75 G00 Z1
N80 X0 Y0
N85 M05
N90 M30

Format: N_ G03 X_ Y_ Z_ I_ J_ K_ F_or N_ G03 X_ Y_ Z_ R_ F_
•The G03 command is
used for all counter
clockwise radial feed
moves, whether they are
quadratic arcs, partial
arcs, or complete circles,
as long as they lie in any
one plane.
• The G03 command is
modal and is subject to a
user-definable feed rate

EXAMPLE: G03 X1 Y1 I0 J-1
•The G03 command requires an
endpoint and a radius in order to
cut the arc.
(X2, Y2) and the end-point is
(X1, Y1).
• To find the radius,
simply measure the incremental
distance from the start point to the
center point of the arc.
• This radius is written in terms
of the X and Y distances.
values are assigned variables

EXAMPLE: G02 X2 Y1 R1
• You can also specify G02 by entering the X and Y
endpoints and then R for the radius. Note: The use of an
R value for the radius of an arc is limited to a maximum
movement of 90°.
• To find I value, calculate difference b/w the arc start
point and center point in the X direction. In this case,
both X values are 2 so the I value is 0.
• To find J value, calculate difference b/w the arc start
point and center point in the Y direction. In this case, the
difference between Y2 and Y1 is down 1 inch, so the J
value is –1.

•The G03 command requires
an endpoint and a radius in
order to cut the arc.
(X4,Y1) and the endpoint
is(X1,Y4).
• To find the radius, simply
measure the incremental
distance from the start point to
the center point.
• This radius is written in
terms of the X and Y distances.
values are assigned variables I
and J, respectively.

Sample Program (G03). Workpiece Size: X4, Y4, Z0.25
Tool: Tool #2, 1/4" Slot Drill
Tool Start Position: X0, Y0, Z1
%
:1004
N5 G90 G20
N10 M06 T2
N15 M03 S1200
N20 G00 X2 Y0.5
N25 Z0.125
N30 G01 Z-0.125 F5
N35 X3 F15
N40 G03 X3.5 Y1 R0.5 (G03 arc using R value) N45 G01 Y3
N50 G03 X3 Y3.5 I-0.5 J0 (G03 arc using I and J) N55 G01 X2
N60 G03 X2 Y1.5 I0 J-1 (180° arc using I and J)
N65 G01 Y0.5
N70 G00 Z0.1
N75 X1.5 Y2.5
N80 G01 Z-0.25 F5
N85 G03 X1.5 Y2.5 I0.5 J0 (Full circle using I and J)
N90 G00 Z1
N95 X0 Y0
N100 M05
N105 M30

G02/G03 Circular Interpolation
• Command Format with IJK Method
(GI7) G02 (or G03) Xx Yy li Ji Ff on XY-plane
(G18) G02 (or G03) Xx Zz li Kk Ff on ZX-plane
(G19) G02 (or G03) Yy Zz Jj Kk Ff on YZ-plane
• Command Format with R Method
(GI7) G02 (or G03) Xx Yy Rr Ff on XY-plane
(G18) G02 (or G03) Xx Zz Rr Ff on ZX-plane
(G19) G02 (or G03) Yy Zz Rr Ff on YZ-plane

G17 = XY plane
G18 = XZ plane
G19 = YZ plane
G02/G03 Circular Interpolation

G28 Automatic Return to Reference
Format: N_ G28 X_ Y_ Z_
primarily used before
automatic tool changing.
• It allows the existing
tool to be positioned to the
predefined reference point
automatically via an
intermediate position.
• This ensures that when
the tool changer is engaged,
it is properly aligned with
the spindle head.
NOTE: When this command is being used, it is advisable for safety reasons to
cancel any tool offset or cutter compensation.

G29 Automatic Return from Reference
•The G29 command can be
used immediately after an
automatic tool change.
• It allows the new tool to be
returned from the predefined
reference point to the specified
point via an intermediate point
specified by the previous G28
command.
NOTE: When this command is being used, it is advisable for safety reasons to
cancel any tool offset or cutter compensation.

G54-G59 Workpiece Coordinate System
Format: N_ G54 Through G59
•The G54 – G59 commands are
used to reposition the origin per
a user- defined working
coordinate system.
• In CNCs six register sets in
the controller hold the values
for the working coordinate
systems.
• The G54 – G59 commands
are very useful when multiple
workpiece fixtures are used.
• On real CNC controllers
these values are held in
parameter fields which are
normally set in the parameters
entry screen of the controller.

G92 Repositioning Origin Point
used to reposition the
origin point.
• The origin point is not a
physical spot on the
machine tool, but rather a
reference point to which the
coordinates relate.
• Generally, the
origin point is located at a
prominent point or object
(for example, front top
left corner of the part) so
that it is easier to
measure from.

G02 Circular Interpolation (CW)
Format: N_ G02 X_ Z_ I_ K_ F_ N_ G02 X_ Z_ R_ F_
• G02 command executes all
circular or radial cuts in a
clockwise motion.
• It is specified by the G02
command, followed by the
endpoint for the move, the radius
(the distance from startpoint to
the centerpoint), and a feedrate.
• 3 requirements for cutting arcs
are:
- The endpoint.
- The radius R or I for X and K
for Z values that represent the
incremental distance from the
startpoint to the centerpoint. The
R value is limited to a maximum
of 90°.
- The feedrate.
CNC Lathe Programming

EXAMPLE: N05 G01 X2 Z-1 F0.012
N10 G02 X0 Z0 I-1 K0 or N10 G02 X0 Z0 R0.5

Sample Program G02
Work piece Size: Length 4", Diameter 2"
Tool: Tool #2, Right-hand Facing Tool
Tool Start Position: X2, Z3
%
:1002
N5 G20 G40
N10 T0202
N15 M03
N20 G00 X1.7
N22 Z0.1 M08
N25 G01 Z-0.5 F0.012
N30 G00 X2
N35 Z0.1
N40 X1.4
N45 G01 Z-0.25
N50 G00 X2.1
N55 Z-1
N60 G01 X2.0
N65 G02 X0 Z0 I-1.0 K0 (90° CW arc feed move)
N70 G00 X2.1
N75 Z-1.0
N80 G01 X2.0
N85 G02 X2.0 Z-2 I0.5 K-0.5 (Partial CW arc feed move)
N90 G00 X4.0 Z3.0 M09
N95 T0200 M05
N100 M30

G03 Circular Interpolation (CCW)
•G03 command executes all radial
cuts in a counter clockwise motion.
• It is specified by the G03
command, followed by the
endpoint for the move, the radius
(the distance from the startpoint to
the center point), and a feed rate.
• The radius is specified by
defining the incremental distance
from the arc’s start-point to its
center-point in both the X and Z
directions. These values are
identified by I and K variables,
respectively. The R word, the value
of the radius of the arc, can also be
used.

EXAMPLE: N10 G01 X0 Z0 F0.012
N15 G03 X2.0 Z-1.0 I0 K-1.0
In this example, the tool cuts a counterclockwise arc from its present
position to (X2, Z–1) at a feedrate of 0.012 ipr

Sample Program G03:
Workpiece Size: Length 4", Diameter 2"
Tool: Tool #2, Right-hand Facing Tool
%
:1003
N5 G20 G40
N10 T0202
N15 M03
N20 G00 X1.7
N22 Z0.1 M08
N25 G01 Z-0.5 F0.012
N30 G00 X2.0
N35 Z0.1
N40 X1.4
N45 G01 Z-0.25
N50 G00 X1.5
N55 Z0.1
N60 X0
N65 G01 Z0
N70 G03 X2.0 Z-1.0 I0 K-1.0 (90° CCW arc feed move)
N75 G01 Z-2.0
N80 G03 X2.0 Z-1.0 I0.5 K0.5 (Partial CCW arc feed move)
N85 G00 X4.0 Z3.0 M09
N90 T0200 M05
N95 M30

G28 Automatic Return to Reference Point
Format: N_ G28 X_ Z_
commonly used prior to an
automatic tool change.
• It allows the existing tool
to be positioned to the
predefined reference point
automatically via an
intermediate position.
• This ensures that when
the tool turret is engaged, it
is properly aligned and
clears the work piece.

The G28 command is commonly used prior to an automatic tool change. It
allows the existing tool to be positioned to the predefined reference point
automatically via an intermediate position. This ensures that when the tool
turret is engaged, it is properly aligned and clears the workpiece.

Sample Program G28:
Workpiece Size: Length 4", Diameter 2.5"
Tool: Tool #1, Right-hand Tool
Tool Start Position: X2", Z3"
Zero Return Position: X2", Z3"
%
:1028
N5 G20 G40
N10 T0101
N12 M03 M08
N15 G00 X2.25
N20 Z0.1
N25 G01 Z-2.0 F0.012
N30 G28 X4.0 Z0.5 M09 (Rapid move to zero return position)
N35 T0100 M05
N40 M30

G29 Automatic Return from Reference Point
The G29 command can
be used immediately
after an automatic tool
change. It allows the new
tool to be returned from
the predefined reference
point to the specified
point via an intermediate
point specified by the
previous G28 command.

Sample Program G29:
Workpiece Size: Length 4", Diameter 2.5"
Tools: Tool #1, Right-hand Tool
Tool #2, Finishing Tool
Tool Start Position: X2", Z3“
Zero Return Position: X2", Z3"
%
:1029
N5 G20
N10 T0101
N12 M03 M08
N15 G00 X2.25
N20 Z0.1
N25 G01 Z-2.0 F0.012
N30 G28 X4.0 Z0.5 M09
N35 T0100 M05
N40 T0202
N45 M03 M08
N50 G29 X2.25 Z0.1 (Return from zero return position)
N55 G01 Z-2.0
N60 G28 X4 Z0.5 M09
N65 T0100 M05
N70 M30

G54 – G59 Working Coordinate System
Format: N_ G54 through G59
•The G54 – G59 commands
are used to reposition the
origin as per a user- defined
working coordinate system.
• Six register sets in the
controller which hold the
values for the working
coordinate systems.
• The G54 – G59 commands
are very useful when
multiple workpiece fixtures
are used.

G98 Set Initial Plane Rapid Default
Format: N_ G98
• The G98 command forces
the tool to return to the Z
initial plane a drilling
operation.
• This forces the tool up
and out of the workpiece.
• This setting is normally
used when a workpiece has
clamps or other obstacles
that could interfere with
tool movement.
• The G98 command is
also
the system default.
CNC Milling Cycles

CNC Milling Cycles
G99 Set Rapid to Retract Plane
Format: N_ G99
•The G99 command forces the
tool to return to the retract
plane after a drilling operation.
• This forces the tool up and
out of the workpiece to the
retract plane specified in the
drilling cycle, overriding the
system default.
• This command is usually
used on drilling cycles within a
pocket, or on workpieces that
do not have surface obstacles.
• It is quicker than the
G98 command because the tool
moves only to the retract plane.

CNC Milling Cycles
G73 High-Speed Peck Drilling Cycle
Format: N_ G73 X_ Y_ Z_ R_ Q_ F_
• During a G73 high-speed peck drilling cycle, the tool
feeds in to the peck distance or depth of cut, then retracts
a small pre-determined distance, which is the chip-
breaking process, and then feeds to the next peck, which
takes the tool deeper.
• This process is repeated until the final Z depth is
reached. Because the tool doesn't retract fully from the
hole, as in the G83 cycle, it minimizes cycle time and
improves total part machining time.

G80 Cancel Canned Cycle
Format: N_ G80
• The G80 command cancels all previous canned cycle
commands. Because the canned cycles are modal (refer to
the canned cycles on the following pages), they will remain
active until canceled by the G80 command.
• Canned cycles include tapping, boring, spot facing, and
drilling.
Note: On most controllers the G00 command will also
cancel any canned cycles.
CNC Milling Cycles

G81 Drilling Cycle
Format: N_ G81 X_ Y_ Z_ R_ F_
• The G81 command invokes a
drill cycle at specified locations.
• This cycle can be used for bolt
holes, drilled patterns, and mold
sprues, among other tasks.
• This command is modal and so
remains active until overridden by
another move command or
cancelled by the G80 command.
Invoking the G81 command requires invoking the Z initial plane, Z
depth and Z retract plane parameters
CNC Milling Cycles

CNC Milling Cycles
G82 Spot Drilling or Counter Boring Cycle
Format: N_ G82 X_ Y_ Z_ R_ P_F_
•This cycle follows the same
operating procedures as the G81
drilling cycle, with the addition of a
dwell.
• The dwell is a pause during
which the Z axis stops moving but the
spindle continues rotating.
• This pause allows for chip
clearing and a finer finish on the
hole.
• The dwell time is measured in
seconds.
• The dwell is specified by the P
letter address, followed by the dwell
time in seconds.
The same Z levels apply to the G82 cycle as to the
G81 cycle: Z initial plane, Z depth and Z retract.

G82 Deep Hole Drilling Cycle
Format: N_ G83 X_ Y_ Z_ R_ Q_F_
• The G83 command involves individual
peck moves in each drilling operation.
• When this command is invoked, the tool
positions itself as in a standard G81 drill
cycle.
• The peck is the only action that
distinguishes the deep hole drilling cycle from
the G81 cycle.
• When pecking, the tool feeds in the
specified distance (peck distance or depth of
cut), then rapids back out to the Z Retract
plane.
• The next peck takes the tool deeper, and
then it rapids out of the hole. This
process is repeated until the final Z depth
is reached.
In the G83 cycle, Q is the
incremental depth of cut.
CNC Milling Cycles

CNC Lathe Cycles
G32 Simple Thread Cycle
Format: N_ G32 Z_ K_ F_
The G32 command invokes a
simple or basic thread cycle. It
automatically synchronizes
spindle and axis movements to
achieve the desired thread
pitch defined by the F word
address.

G32 Simple Thread Cycle
Sample Program G32EX32:
Tool: Tool #4, Neutral Tool / Threading Tool
%
:1040
N5 G20 G40 (Set TNR cancel at beginning)
N10 T0101
N15 M03 M08
N20 G00 Z0.1
N25 X2.1
N30 G01 X1.0 F0.012
N35 G32 Z-2.0 F.05 (Machine a single-pass thread)
N40 G00 X4.0
N45 T0100 M05
N50 M30
CNC Lathe Cycles

G70 Finishing Cycle
Format: N_ G70 P_ Q_
•The G70 command is used
immediately after a roughing
cycle, such as a G71 Rough
Turning, or G72 Rough Facing
cycle command.
• The remaining material is
machined as specified by the P
and Q block number values,
which point to the start and
finish blocks of the desired part
profile contour
CNC Lathe Cycles

G70 FINISHING CYCLE Format: N_ G70 P_ Q_
P Start block of segment
Q End block of segment
F Feedrate
G71 ROUGH TURNING CYCLE Format: N_ G71_
P_ Q_ U_ W_ D_ F
P Start block of segment
Q End block of segment
U Amount of stock to be left for finishing in X
W Amount of stock to be left for finishing in Z
D Depth of cut for each pass in thousandths
F Feedrate for finish pass
CNC Lathe Cycles

G71 Rough Turning Cycle
Format: N_ G71_ P_ Q_ U_ W_ D_ F _
•The G71 command automatically
generates roughing passes to turn a
workpiece to a specified profile,
leaving an allowance for finishing.
• It reads a program segment
specified by the P and Q letter
addresses and determines the number
of passes, the depth of cut for each
pass, and the number of repeat passes
for the cycle.
• Cutting is done parallel to the Z
axis. The U and W signs determine
the direction of the cuts.
CNC Lathe Cycles

G71 Rough Turning Cycle
Sample Program G71:
Workpiece Size: Length 4", Diameter 2" Tools:
Tool #1, Right-hand Facing Tool
Tool #2, Right-hand Finishing Tool
%
:1071
N5 G90 G20
N10 T0101
N15 M03
N20 G00 X2 Z0.1 M08
N35 G71 P40 Q55 U0.05 W0.05 D625 F0.012 (Rough turning)
N40 G01 X0 Z0
N45 G03 X1 Z-0.5 I0 K-0.5
N50 G01 Z-1.0
N55 X2.1 Z-1.5
N60 T0100 G00 X4 Z3
N65 T0202
N70 G00 X2 Z0.1
N75 G70 P40 Q55 F0.006
N80 G00 X4 Z3 M09
N85 T0200 M05
N90 M30
CNC Lathe Cycles

CNC Lathe Cycles
G72 Rough Facing Cycle
P Start block
Q End block
U Amount of stock to be left for finishing in X
W Amount of stock to be left for finishing in Z
D Depth of cut for finish pass
F Feedrate (this is optional)
The G72 command automatically faces off a part to a
predefined depth of cut, with preset offsets and feed rates.

• The G72 command
automatically faces off a part to
a predefined profile, with preset
offsets and feedrates leaving an
allowance for finishing.
• It reads a program segment
specified by the P and Q letter
addresses and determines the
number of passes, the depth of cut
for each pass, and the number of
repeat passes for the cycle.
• Cutting is done parallel to
the X axis. The U and W signs
determine the direction of the
cuts.
CNC Lathe Cycles

Sample Program G72:
Tools: Tool #1, Right-hand Facing Tool
Tool #2, Right-hand Finishing Tool
%
:1072
N5 G90 G20
N10 T0101
N15 M03
N20 G00 X1 Z0.1 M08
N25 G72 P30 Q50 U0.05 W0.05 D500 F0.012 (Rough facing)
N30 G01 X0 Z0.1
N35 X0.25
N40 Z-0.125
N45 X0.5 Z-0.25
N50 G02 X1 Z-0.5 I0.25 K0
N55 G00 X4 Z3 T0100
N60 T0202
N65 G00 X1 Z0.1
N70 G70 P30 Q50 F0.006
N75 G00 X4
N80 Z3 M09
N85 T0200 M05
N90 M30
CNC Lathe Cycles

CNC Lathe Cycles
G74 Peck Drilling Cycle
Format: N_ G74_ X0 Z_ K_ F _
EXAMPLE: N20 G74 X0 Z-1.0 K0.125 F0.015
In this example, a hole is peck drilled to a total depth of 1 in., using 0.125 in.
for each peck
•The G74 command executes
a peck drilling cycle
with automatic retracts and
incremental depths of cut. The
G74 command is specified by
several letter addresses:
X0 X always 0
Z Total depth
K Peck depth
F Feed rate

G74 Peck Drilling Cycle
Sample Program G74:
Workpiece Size: Length 4", Diameter 1" Tools: Tool #12, Center Drill
Tool #10, 1/2" Drill
%
:1074
N5 G20 G98
N10 T1212 M08
N15 M03 S2000
N20 G00 X0
N25 Z0.1
N30 G01 Z-0.2 F2
N35 G00 Z3
N40 X3 T1200
N45 T1010
N50 G00 X0
N55 Z0.1
N60 G74 X0 Z-1.5 K0.125 F0.5 (Drilling cycle) N65 G00 Z3
N70 X4 M09
N75 T1000 M05
N80 M30
CNC Lathe Cycles

CNC Lathe Cycles
G75 Grooving Cycle
Format: N_ G75 X_ Z_ F_ D_ I_ K_
X Diameter of groove
Z Z position of groove
F Incremental retract
D Depth/X offset
K Z movement
I X movement
The G75 command is used to machine
grooves.
EXAMPLE: N25 G75 X0.25 Z-0.75 F0.125 I0.125 K0.125
This command defaults to the last specified feedrate. The F address is used
to specify the retract distance, so the feedrate cannot be set within the
grooving cycle

CNC Lathe Cycles
G75 Grooving Cycle
Sample Program G75:
Tool: Tool #5, Grooving Tool
%
:1075
N5 G90 G20
N10 T0505 F0.015
N15 M03
N20 G00 Z-0.5 M08
N25 X1.2
N30 G75 X0.5 Z-0.75 F0.125 D0 I0.125 K0.125 (Grooving cycle)
N35 G00 X4
N40 Z3 M09
N45 T0500 M05
N50 M30

G76 Threading Cycle
Format: N_ G76 X_ Z_ F_ D_ IA_ K_
The G76 command performs all threading operations in a cycle, with
automatic depth change and tool path calculation. The G76 command is
specified by several letter addresses:
X Minor diameter of thread
Z Position at end of thread
D Depth of first pass in thousandths (the control uses the first depth
of cut to determine the number of passes)
K Depth of thread
F Pitch of thread (thread pitch = 1/thread/in.)
A Tool angle (If the tool angle is given, the tool will continue to cut
on the leading edge of the tool; if no tool angle is given, the tool
will cut on both sides.)
EXAMPLE: N25 G76 X0.5 Z-1.0 D625 K0.25 A55 F0.1
In this example, the tool cuts a thread, starting at its present location and
ending at the specified XZ endpoint. The D value specifies each cut depth,
and the K value defines the overall depth. The A value defines the tool angle,
and the F value defines pitch
CNC Lathe Cycles

G76 Threading Cycle
Format: N_ G76 X_ Z_ F_ D_ IA_ K_
CNC Lathe Cycles

G76 Threading Cycle
Sample Program G76:
Tool: Tool #6, Neutral Tool
%
:1076
N5 G90 G20
N10 T0606 M08
N15 M03
N20 G00 X1
N25 Z0.1
N25 G76 X0.96 Z-2 D625 K0.125 A55 F0.1 (Threading cycle)
N30 G00 X4
N35 Z3 M09
N35 T0600 M05
N40 M30
CNC Lathe Cycles

N10 G17 G54 ;Working plane X/Y, workpiece zero
N20 TRANS X20 Y10 ;Absolute offset
N30 L10 ;Subprogram call
N40 TRANS X55 Y35 ;Absolute offset
N50 AROT RPL=45 ;Rotation of the coordinate system through 45°
N70 TRANS X20 Y40 ;Absolute offset; (cancels all previous offsets)
N80 AROT RPL=60 ;Additive rotation through 60°
N100 G0 X100 Y100 ;Retraction
N110 M30 ;End of program
Advanced programming command
1. TRANS, ATRANS
2. ROT, AROT
Example using the command:
A feature(ex:pocket) can be translated
or rotated as shown in the figure.

1. SCALE, ASCALE
2. MIRROR, AMIRROR
Advanced programming command
Ex for TRANS, AROT and ASCALE Command Ex for MIRROR, AMIRROR Command
Ex for SCALE, ASCALE Command
A feature(ex:pocket) can be scaled or
mirrored as shown in the figure.

Automatic Part Programming
Software programs can automatic generation of CNC data
Make 3D model
Define Tool
CNC data
Simulate
cutting

Programming is where all the machining data are compiled and where the
data are translated into a language which can be understood by the
control system of the machine tool. The machining data is as follows
CNC PART PROGRAMMING
(a) Machining sequence classification of process, tool start up point,
cutting
depth, tool path, etc.
(b) Cutting conditions, spindle speed, feed rate, coolant, etc.
(c) Selection of cutting tools

While preparing a part program, need to perform the following steps :
(a) Determine the startup procedure, which includes the extraction of
dimensional data from part drawings and data regarding surface
quality
requirements on the machined component.
(b) Select the tool and determine the tool offset.
(c) Set up the zero position for the workpiece.
(d) Select the speed and rotation of the spindle.
(e) Set up the tool motions according to the profile required.
(f) Return the cutting tool to the reference point after completion of
work.
(g) End the program by stopping the spindle and coolant.

Manual Part Programming
The programmer first prepares the program manuscript
in a standard format. Manuscripts are typed with a
device known as flexo writer, which is also used to type
the program instructions
To be able to create a part program manually, need the following
information :
(a)Knowledge about various manufacturing processes and machines.
(b) Sequence of operations to be performed for a given component.
(c) Knowledge of the selection of cutting parameters.
(d) Editing the part program according to the design changes.
(e) Knowledge about the codes and functions used in part programs.

Computer Aided Part Programming
If the complex-shaped component requires calculations to produce the
component are done by the programming software contained in the
computer. The programmer
communicates with this system through the system language, which is
based on words.
There are various programming languages developed in the recent
past, such as APT (Automatically Programmed Tools), ADAPT,
AUTOSPOT, COMPAT-II, 2CL, ROMANCE, SPLIT is used for writing a
computer programme, which has English like statements. A translator
known as compiler program is used to translate it in a form
acceptable to MCU.
The programmer has to do only following things :
(a) Define the work part geometry.
(b) Defining the repetition work.
(c) Specifying the operation sequence.

Interactive Graphic System in Computer Aided Part Programming
Computer Aided Part Programming

Element for developing part program
Type of Dimensioning System
We determine what type of dimensioning system the machine uses, whether an
absolute or incremental dimensional system
CNC Machines
Axis Designation
The programmer also determines how many axes are availed on machine tool.
Whether machine tool has a continuous path and point-to-point control system.
NC Words
The NC word is a unit of information, such as a dimension or feed rate and so on. A
block is a collection of complete group of NC words representing a single NC
instruction. An end of block symbol is used to separate the blocks. NC word is where
all the machining data are compiled and where the data are translated in to a
language, which can be understood, by the control system of the machine tool.
Block of Information
NC information is generally programmed in blocks of words. Each word conforms to
the EIA standards and they are written on a horizontal line. If five complete words
are not included in each block, the machine control unit (MCU) will not recognize
the information; therefore the control unit will not be activated. It consists of a
character N followed by a three digit number raising from 0 to 999.

Standard G and M Codes
The most common codes used when programming NC machines
tools are G-codes (preparatory functions), and M codes
(miscellaneous functions). Other codes such as F, S, D, and T are
used for machine functions such as feed, speed, cutter diameter
offset, tool number, etc. G-codes are sometimes called cycle codes
because they refer to some action occurring on the X, Y, and/or Z-
axis of a machine tool. The G-codes are grouped into categories
such as Group 01, containing codes G00, G01, G02, G03, which
cause some movement of the machine table or head. Group 03
includes either absolute or incremental programming. A G00 code
rapidly positions the cutting tool while it is above the workpiece from
one point to another point on a job. During the rapid traverse
movement, either the X or Y-axis can be moved individually or both
axes can be moved at the same time. The rate of rapid travel varies
from machine to machine.

Tape Programming Format
Both EIA and ISO use three types of formats for compiling of NC data into
suitable blocks of information with slight difference.
Word Address Format
This type of tape format uses alphabets called address, identifying the function of
numerical data followed. This format is used by most of the NC machines, also
called variable block format. A typical instruction block will be as below :
N20 G00 X1.200 Y.100 F325 S1000 T03 M09 <EOB>
or
N20 G00 X1.200 Y.100 F325 S1000 T03 M09;
The MCU uses this alphabet for addressing a memory location in it.
Tab Sequential Format
Here the alphabets are replaced by a Tab code, which is inserted between two
words. The MCU reads the first Tab and stores the data in the first location then
the second word is recognized by reading the record Tab. A typical Tab sequential
instruction block will be as below :
>20 >00 >1.200 >.100 >325 >1000 >03 >09
Fixed Block Format
In fixed block format no letter address of Tab code are used and none of words
can be omitted. The main advantage of this format is that the whole instruction
block can be read at the same instant, instead of reading character by character.
This format can only be used for positioning work only. A typical fixed block
instruction block will be as below: 20 00 1.200 .100 325 1000 03 09 <EOB>

Machine Tool Zero Point Setting
The machine zero point can be set by two methods by the operator,
manually by a programmed absolute zero shift, or by work coordinates, to
suit the holding fixture or the part to be machined.
Manual Setting
The operator can use the MCU controls to locate the spindle over the
desired part zero and then set the X and Y coordinate registers on the
console to zero.
Absolute Zero Shift
The absolute zero shift can change the position of
the coordinate system by a command in the CNC
program. The programmer first sends the machine
spindle to home zero position by a command in the
program. Then another command tells the MCU
how far from the home zero location, the coordinate
system origin is to be positioned

Coordinate Word
A co ordinate word specifies the target point of the tool movement or the
distance to be moved. The word is composed of the address of the axis to
be moved and the value and direction of the movement.
Example
X150 Y-250 represents the movement to (150, 250). Whether the
dimensions are absolute or incremental will have to be defined previously
using G-Codes.
Parameter for Circular Interpolation
These parameters specify the distance measured from the start point of the
arc to the center. Numerals following I, J and K are the X, Y and Z
components of the distance respectively.
Spindle Function
The spindle speed is commanded under an S address and is always in
revolution per minute. It can be calculated by the following formula :
Surface cutting speed in m/min = 1000 Spindle Speed / π × Cutter
Diameter in mm

Feed Function
The feed is programmed under an F address except for rapid traverse. The
unit may be in mm per minute or in mm per revolution. The unit of the federate
has to be defined at the beginning of the programme. The feed rate can be
calculated by the following formula :
Feet Rate = Chip Load /Tooth × No. of tooth x Spindle speed
Example
F100 represents a feed rate of 100 mm/min.

Work Settings and offset
All NC machine tools require some form of work setting, tool setting, and offsets
to place the cutter and work in the proper relationship. Compensation allows the
programmer to make adjustments for unexpected tooling and setup conditions.
A retraction point in the Z-axis to which the end of the cutter retracts above the
work surface to allow safe table movement in the X-Y axes. It is often called the
rapid-traverse distance, retract or work plane. Some manufacturers build a
workpiece height distance into the MCU (machine control unit) and whenever
the feed motion in the Z-axis will automatically be added to the depth
programmed.
When setting up cutting tools, the operator generally places a tool on top of the
highest surface of the work piece. Each tool is lowered until it just touches the
workpiece surface and then its length is recorded on the tool list. Once the work
piece has been set, it is not generally necessary to add any future depth
dimensions since most MCU do this automatically.

Rapid Positioning
This is to command the cutter to move
from the existing point to the target point at
the fastest speed of the machine.
Linear Interpolation
This is to command the cutter to move
from the existing point to the target point
along a straight line at the speed
designated by the F address
This is to command the cutter to move from
the existing point to the target point along a
circular arc in clockwise direction or counter
clockwise direction. The parameters of the
center of the circular arc is designated by I,
J and K addresses. I is the distance along
the X-axis, J along the Y, and K along the
Z. This parameter is defined as the vector
from the starting point to the center of the
arc.

Circular Interpolation
Tool Path without Cutter Compensation Tool Path with Cutter Compensation
In NC machining, if the cutter axis is moving along the programmed path,
the dimension of the workpiece obtained will be incorrect since the
diameter of the cutter has not be taken in to account. What the system
requires are the programmed path, the cutter diameter and the position of
the cutter with reference to the contour. The cutter diameter is not
included in the programme. It has to be input to the NC system in the tool
setting process

Symbols used
% – Main Programme (1 to 9999)
L – Sub program (1 to 999)/Home position
N – Sequence of block number.
Lf – Block end (EOB) means “; or *”
T – Tool number or Tool station number
D – Tool offset
S – Spindle speed
F – Feed
M – Switching function
G – Transverse commands
R – Parameters
I, J, K – Circle parameters
B/U/R – Radius
X/Y/Z – Axis coordinates
P – Passes.

The CNC lathe operation such as simple facing, turning, taper turning,
thread, boring, parting off etc. The X-axis and Z-axis are taken as the
direction of transverse motion of the tool post and the axis of the spindle
respectively. To prepare part programs using G-codes and M-codes. The
following examples illustrated the part program for different components.
Lathe programming Examples

The CNC milling machine, the motion is possible in three axes, X-axis, Y-axis
and Z-axis. The movement of Z-axis is taken as positive when tool moves
away from the job or vice versa

FIXED CYCLE/CANNED CYCLE
Machining holes is probably the most common operation, mainly done on CNC
milling machines and machining centers. Machining on simple hole may require
only one tool but a precise and complex hole may require several tools to be
completed. Number of holes required for a given job is important for selection of
proper programming approach. In the majority of programming applications,
hole operations offer a great number of similarities from one job to another.
These sequences are referred to in a number of ways like cycle, subroutines
and loops, etc.
A fixed cycle is a combination of machine moves resulting in a particular
machining function such as drilling, milling, boring and tapping. By programming
one cycle code number, as many as distinct movements may occur. These
movements would take blocks of programme made without using Fixed or
Canned cycles. The corresponding instructions of a fixed cycle are already
stored in the system memory. The advantages of writing a part programme with
these structures are :
(a) Reduced lengths of part programme.
(b) Less time required developing the programme.
(c) Easy to locate the fault in the part programme.
(d) No need to write the same instructions again and again in the programme.
(e) Less memory required in the control unit.

The following examples are some basic and fixed cycle codes
available with a number of machines, assigned by EIA
01 (G81 Drilling Cycle) (All dimensions are in mm).
R00 – Dwell time at the starting point for chip removal.
R02 – Reference plane absolute with sign.
R03 – Final depth of hole absolute with sign.
R04 – Dwell time at the bottom of drilled hole for chip breaking.
R10 – Retract plane without sign.
R11 – Drilling axis number 1 to 3.
% 400;

In a few jobs some portion of the programme needs to be repeated, which do not
fit into standardized category. Some of the non-standardized cycles are Do-loops
and Subroutines. Do-loop is a number of operations repeated over a number of
equal steps for a previously fixed number of times.
Do-loops always are implemented on incremental mode because each previous
position becomes reference for next iteration. Do-loop is actually jumping back to
an already written initial portion of the program for the number of times a loop
count
DO LOOP

A subroutine is a portion of a programme, complete in itself, which is
stored in computer after programming once. It is called with required
data when required again in a programme.
SUBROUTINE

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