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1. Computer Numerical Control
Programming Basics
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Definitions
CAD – COMPUTER-AIDED-DESIGN
■ Designing the part to be machined by CNC machine
CAM – COMPUTER-AIDED-MANUFACTURING
■ Developing the toolpaths, feeds and speeds for the CNC Machines
CNC – COMPUTER-NUMERICAL-CONTROLLED
■ Computer controlled machine controlled by a Machine Control Unit
(MCU)
Programming Process
CAD - DRAW PART IN AUTOCAD OR AUTODESK INVENTOR
Program Transfer – Load drawing file into MasterCAM
CAM – PROGRAM CUTTERS, TOOLPATHS, SPEEDS, FEEDS, ETC. IN
MASTERCAM
Post Processor - A software link in the CAD/CAM chain that communicates
instructions from CAM to a CNC machine.
.
Program data transfer - PC to Machine Control Unit which runs the CNC machine
CNC – MACHINE PART ON A CNC MACHINE USING INSTRUCTIONS FORM
CAD/CAM PROGRAMMING

2. CNC Machine Types
CNC Milling Center
CNC Turning Center
CNC Gantry Router

3. What is a CNC Machine?
CNC : Computer and Numeric Control:
Conventionally, an operator decides and adjusts various machines parameters like feed ,
depth of cut etc depending on type of job , and controls the slide movements by hand. In
a CNC Machine functions and slide movements are controlled by motors using computer
programs.
● Programmed instructions are converted into output signals which in turn control
machine operations such as spindle speeds, tool selection, tool movement, and
cutting fluid flow.
● A numerical control, or “NC”, system controls many machine functions and
movements which were traditionally performed by skilled machinists.
● Numerical control developed out of the need to meet the requirements of high
production rates, uniformity and consistent part quality.
Advantages:
● High Repeatability and Precision e.g. Aircraft parts
● Volume of production is very high
● Complex contours/surfaces need to be machined. E.g. Turbines
● Flexibility in job change, automatic tool settings, less scrap
● More safe, higher productivity, better quality
● Less paper work, faster prototype production, reduction in lead times
Disadvantages:
● Costly setup, skilled operators
● Computers, programming knowledge required
● Maintenance is difficult
How CNC works:
● Controlled by G and M codes.
● These are number values and co-ordinates.
● Each number or code is assigned to a particular operation.
○ Typed in manually to CAD by machine operators.
○ G&M codes are automatically generated by the computer software.
● The tool or material moves.
● Tools can operate in 1-5 axes.
● Larger machines have a machine control unit (MCU) which manages operations.
● Movement is controlled by a motor (actuators).
● Feedback is provided by sensors (transducers) Closed loop?
● Tool magazines are used to change tools automatically.

4. Tool Paths, and Cutting Motions:
● Tool paths describe the route the cutting tool takes.
● Motion can be described as point to point, or contouring.
● Speeds are the rate at which the tool operates e.g. rpm.
● Feeds are the rate at which the cutting tool and work piece move in relation to
each other. Expressed in IPM (inches per minute)
● Feeds and speeds are determined by cutting depth, material and quality of finish
needed. e.g. harder materials need slower feeds and speeds.
● Rouging cuts remove larger amounts of material than finishing cuts.
● Rapid traversing allows the tool or work piece to move rapidly when no
machining is taking place
Point to Point and Contour Tool Paths:
Point to Point Toolpath Contour ToolPath
Point to Point toolpaths cut following lines Contour toolpaths cut follow surfaces
Linear Interpolation :( Point to Point)
Linear interpolation consist of a programmed point linked together by straight lines
Circular Interpolation: (Contour) Circular interpolation is the process of programming
arcs and circles.
.
Circular interpolation requires endpoints, a feed rate, a
center, a radius, and a direction of movement.

5. CNC Programming Basics
Block of Information:
When running, a part program is interpreted one command line at a time until all lines are
completed.
N001 G01 X1.2345 Y.06789 MO3
N001 Represents the sequence number of the operation
G01 Represents linear operation (tool movement)
X12345 Will move the tool or table 1.2345 in. a positive direction along the X axis
Y6789 Will move the tool or table 0.6789 in. along the Y axis
M03 Turns spindle on clockwise
Commands, which are also referred to as blocks, are made up of words which each begin
with a letter address and end with a numerical value.
Each letter address relates to a specific machine function. “G” and “M” letter addresses
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

6. G- CODES (Preparatory Functions) which cause some movement of the machine table
or head.
G00 – Rapid Movement
G01 Linear Interpolation (movement)
G02 Circular Interpolation, CW
G03 Circular Interpolation, CCW
G17 XY Plane,G18 XZ Plane,G19 YZ Plane
G20/G70 Inch units
G21/G71 Metric Units
G40 Cutter compensation cancel
G41 Cutter compensation left
G42 Cutter compensation right
G43 Tool length compensation (plus)
G43 Tool length compensation (plus)
G44 Tool length compensation (minus)
G49 Tool length compensation cancel
G80 Cancel canned cycles
G81 Drilling cycle
G82 Counter boring cycle
G83 Deep hole drilling cycle
G90 Absolute positioning

7. G91 Incremental positioning
M-CODES (Miscellaneous) which turn ON or OFF different functions
M00 Program stop
M01 Optional program stop
M02 Program end
M03 Spindle on clockwise
M04 Spindle on counterclockwise
M05 Spindle stop
M06 Tool change
M08 Coolant on
M09 Coolant off
M10 Clamps on
M11 Clamps off
M30 Program stop, reset to start
Important things to know:
Feed rate and spindle speed
● Feed and Speed Codes: F and S- Specify feed and spindle speed
Coolant Control: On/Off, Flood, Mist
Tool Control: Tool and tool parameters
● Tool codes: T – specify tool number
Programming consists of a series of instructions in form of letter codes
Preparatory Codes:
● G codes- Initial machining setup and establishing operating conditions

8. ● N codes- specify program line number to executed by the MCU
Axis Codes: X,Y,Z - Used to specify motion of the slide along X, Y, Z direction
Program Example
O1234 (Program Number)
N5 G90 G20 (ABSOLUTE COORDINATE. IN INCHES)
N10 M06 T3 (TOOLCHANGE TO TOOL #3)
N15 M03 S1250 (SPINDLE ON CW AT 1250RPM)
N20 G00 X1 Y1 (RAPID OVER TO X1 Y1)
N25 Z0.1 (RAPID DOWN TO Z0.1)
N30 G01 Z-0.125 F5 (FEED DOWN TO Z-0.125 AT 5IPM)
N35 X3 Y2 F10 (FEED DIAGONALLY TO X3 Y2 AT 10IPM)
N40 G00 Z1 (RAPID UP TO Z1)
N45 X0 Y0 (RAPID OVER TO X0 Y0)
N50 M05 (SPINDLE OFF)
N55 M30 (PROGRAM END