CO-ORDINATE SYSTEM

CO-ORDINATE SYSTEM

Before going further into programming it is necessary to know some fundamental details
regarding directions of tool movement, sign convention followed for directions of tool travel and
axes co-ordinate system, different methods of dimensioning, units of dimensioning system etc.,

1. CO-ORDINATE AXES :
The directions of movement in a machine tool are based on a co-ordinate system allocated
to the axes of motion of the slides.
As in the conventional lathe there is movement of slides in two directions along two axes,
one axis being parallel to the spindle axis ( Z-AXIS) and the other axis perpendicular to the spindle
axis (X- AXIS).
The axis parallel to the spindle axis is called Z-axis. The axis perpendicular to the spindle
axis is called X-axis.
Since the machine co-ordinate system has two axes, X and Z, it is referred to as the X-Z
co-ordinate system

2. DIRECTIONS OF MOVEMENT :
Consider that a tool is positioned in I quadrant of X-Z co-ordinate system.
Conventionally speaking,
Along Z-axis any movement towards the spindle is considered as movement in the
negative direction and any movement away from the spindle is considered as movement in
the positive direction.
Along X-axis any movement towards the operator is considered as movement in the
negative direction and any movement away from the operator is considered as movement
in the positive direction.

TYPES OF CO-ORDINATE SYSTEMS:-

1. Absolute Co-Ordinate system
2. Incremental  Co-Ordinate system

Absolute Co-Ordinate system:-

In the figure, X and Z axes are divided into equal increments on either side of the origin.

To represent a point “P1” which is located at 3 divisions to the right of the origin along Zaxis

and 4 dimensioning above the origin along X-axis, it is written as P1(X4,Z3). The

positive value for X and Z is given because the point is located in the positive direction

with respect to origin in both the axes.

Similarly to represent P2, P2 is written as P2(X5,Z-3) as it is in the positive direction along

X-axis and in the negative direction along Z-axis. Thus all the points are referred to the

fixed origin. The origin is also called as ABSOLUTE ZERO or FIXED ZERO. Since all

the co-ordinate are defined with respect to fixed zero, this system is also called as FIXED

ZERO SYSTEM OF DIMENSIONING

INCREMENTAL SYSTEM 

With incremental system of dimensioning, target point co-ordinates do not refer to the

fixed zero. Target point co-ordinates will be defined with respect to present position.

Assuming that tool is positioned at point P0, if a reference is made for point P1, coordinates

of P1 are defined with respect to point P0.

Co-ordinates of P1 with respect to P0 are X4Z3.

Similarly if a reference is made for point P2, co-ordinates of P2 with respect to P1 are

X4Z5.

Again if a reference is made for P0, co-ordinates of P0 with respect to P2 are X-8Z-8.

Thus incremental system doesn’t have a fixed origin. The origin changes from point to

point. In other words the origin is floating and hence FLOATING ZERO SYSTEM OF

DIMENSIONING.

Co-ordinates of P1 with respect to P0 are X4 Z3

Co-ordinates of P2 with respect to P1 are X4 Z5

Co-ordinates of P0 with respect to P2 are X8 Z8

CNC PROGRAMMING INTRODUCTION

CNC programming is the language  which is understand by the cnc machines. If you want talk  to the machine you need to learn the language of  the CNC machines . If you want to move the machine in left, right, up & down you need to give the command to the machine in the language of the machine so that it will be under stand.

PROGRAM :
To machine a component on a CNC machine, information like co-ordinate values and other
technical data which indicate, how, a tool should be moved in relation to a work piece to
achieve a desired machining form, is to be given in the form of coded instructions to the
control unit. These information are called a “PART PROGRAM”.

AXIS NOMENCLATURE :



Standard right hand Cartesian co-ordinate system is used. Always cutting tool moves with
respect to the work piece. ( Lathe machine )

X-AXIS : Always parallel to the work-holding surface or perpendicular to main axis.

Z-AXIS : It is always the main spindle axis.

C-AXIS : It is rotating axis about Z -AXIS.

PROGRAM STRUCTURE :

Part program comprises of a string of blocks written one after the other. When writing a program,
a particular syntax is to be followed.
As per part program structure :

                    A. Program starts with program number.

                    B. Consists of series of blocks – dimensional and non-dimensional data like feed,                                         speed,auxiliary functions etc.,

                    C. Program ends with program end code.

Character for program start, precedes the first block in the part program.
Character for main program start is given by “O”
To start program 1 – O 0001
To start program 2 – O 0002
Program start can also be called as program numbering. The program number is useful in
identification of a program and calling a program.

PROGRAM BLOCKS :

Program blocks contain data required to execute an operation. It is possible to write the program
blocks with or without a sequence number. Sequence number is given at the block head. It need
not be consecutive. It is used for the convenience of the operator. Sequence number is of 4 digits.

Examples :
              * N0005 G00X20.Z5. ; Program block written with block number.
                  G00X20.Z5. ; Program block written without block number.

All the blocks end with block end character ; or ✫
If no block number is given or same block number is given to several blocks, then there cannot be
a defined program jump or block search.

PROGRAMMING WORD :

A program is made up a number of blocks. Similarly a block is made up a number of words.
A word consists of an address character and a string of digits (alphanumeric character).
An address character is normally an alphabet.
X,Z,S,F ….. are all address characters.

N         Address of block number
G         Preparatory function
X         Axes address
Z          Axes address
F         Feed rate
S         Spindle speed
T         Tool number
M        Miscellaneous function
;           Block end character

WHAT IS THE CNC

CNC  stands for Computer Numerical control  in this machines the motions of machine is contrilled by  numeric values .
Today  in industry the conventional machines has been replace  by  the CNC machines .

because the CNC machines takes less time to complete the jobs. these machines are more accurate than conventional machines. CNC machines not required more skill person to complete the job as compared to the conventional machines. So Today if you want to survive manufacturing industry knowledge of CNC  machines and CNC machine language  (G-coad  programming) is more important

Cnc lathe machines 

Conventional lathe machine

Conventional milling machine

Cnc milling machine

Advantages of CNC

CNC has many advantages over manual machining including:

- Setup Time Reduction

- Lead Time Reduction

- Accuracy and Repeat-ability

- Contouring of Complex Shapes

- Simplified Tooling and Work holding

- Cutting Time and Productivity Improvements

If are you want to learn cnc programming then it is the right place for you you just need to basic knowledge of cnc and most important interest in cnc programming .

we start learning cnc programming  of two axis (lathe)  then more then three axis machines ( vmc milling  machines)

Types of CNC Machines 

 CNC machines can be classified in many ways.

 According to NO. of Axis 

1 Two axis machines 

    for example  lathe machines grading machines etc.

2. More than two axis 

     for example milling machines (VMC) ,Hobbing machines