This document provides details about a summer training project report on computer numerical control (CNC) machines completed by Amarkant Anchal at Bharat Heavy Electricals Limited in Jhansi, India under the guidance of Mr. Sateesh Soni. The report includes sections on CNC construction details, coordinate systems, positioning of the machine origin, motion control systems, part programming, and advantages of CNC machines. It also provides acknowledgements, a preface, index, and several chapters discussing topics like numerical control and applications of CNC.

1. SUMMER TRAINING & PROJECT REPORT
ON
CNC
DEVELOPED
AT
BHARAT HEAVY ELECTRICALS LIMITED,
JHANSI
UNDER THE GUIDANCE OF-
MR. SATEESHSONI
(DPT.MANAGER)
BHEL, JHANSI
SUBMITTED TO- SUBMITTED BY-
DR. MD. AFTAB ALAM AMARKANT ANCHAL
( HRD) B.TECH(branch-E.C.E)
B.H.E.L JHANSI (UP) IETBU JHANSI

2. CERTIFICATE
This is to certify that project report entitled “COMPUTER
NUMERICAL CONTROL” submitted by “AMARKANT
ANCHAL” (B.Tech 3rd year ELECTRONICS &
COMMUNICATION ENGINEERING) in the partial fulfillment
of the requirement for the certificate of training completion with
excellence in knowledge at “BHARAT HEAVY
ELECTRICALS LIMITED, JHNASI” is an authentic work
carried out by him under my supervision during the month of
June 2019.
Date:
Mr.Sateesh Soni
Place: JHANSI BHEL, JHANSI

3. ACKNOWLEDGEMENT
I am highly thankful to B.H.E.L. engineers and technical staff for providing us
vital and valuable information about the different facets of an industrial
management system.
We express our gratitude to Human Resource and Development department for
giving us a chance to feel the industrial environment and its working in B.H.E.L.
and we are thankful to Mr. Md. Aftab Alam, DGM, HRD for giving his precious
time and help us in understanding various theoretical and practical aspect of our
project on PLC under whose kind supervision we accomplished our project. We
are also thankful to Mr. Sateesh Soni for his kind support.
AmarkantAnchal
B.TECH (Electronics &
Communication
Engineering)

4. PREFACE
At very outset of the prologue it becomes imperative to insist that vocational
training is an integral part of engineering curriculum. Training allows us to gain an
insight into the practical aspects of the various topics, with which we come across
while pursuing our B.E. i.e. vocational training gives us practical implementation
of various topics we already have learned and will learn in near future. Vocational
training always emphasizes on logic and commonsense instead of theoretical
aspects of subject.
On my part, I pursued 2 weeks training at B.H.E.L. Jhansi. The training involved a
study of various departments of the organization as per the time logically
scheduled and well planned given to us. Italso involved a project on PLC under
the guidanceof Mr. Sateesh Soni (Sr. Engineer in W, E & S Department).
The rotation in various departments was necessary in order to get an overall idea
about the working of the organization.
Amarkant Anchal
BE(Electronics
&Communication
Engineering)

5. INDEX
CHAPTER NO & TITLE PAGE NO.-
1-Computer Numeric Control (CNC) 07
-CNC Constructional details 08
-CNC coordinate systems 11
-Positioning of machine origin 12
-CNC motion control systems 14
-Part programming 25
-Advantages of CNC machine 26
2-Numerical control (NC) and computer numerical
control (CNC) 27
3-Applications 39
4-References 40

6. PROJECT REPORT ON
computer numerical control
machines (cnc)

7. CHAPTER-1
C.N.C (COMPUTER NUMERIC CONTROL)
Many of the achievement in computer numeric control have a common origin in numerical control
(abbreviated nc). The conceptual framework established during the development of numerical control is
still undergoing further refinement and enhancement. Modern nc systems rely heavily on computer
technology.
Nc (numerical control):-
Numerical control can be defined as a form of programmable automation in which the process is
controlled by numbers, letters, and symbols. Numerical control is the combination of mechanical,
electrical and electronic devices, controlled by numerical data. In nc, the numbers form a program of
instructions designed for a particular work part or job. When the job changes, the program of instructions
is changed. This capability to change the program for each new job is what gives nc its flexibility. It is
much easier to write new programs than to make major changes in the production equipment.
Nc technology has been applied to a wide variety of operations, including drafting, assembly, inspection,
sheet metal press working, and spot welding. However numerical control finds its principal applications
in metal machining processes. The machined work parts are designed in various sizes and shapes, and
most machined parts produced in industry today are made in small to medium-size batches. To produce
each part, a sequence of drilling operations may be required, or a series of turning or milling
operations. The suitability of nc or these kinds of jobs is the reason for the tremendous growth of
numerical control in the metal working industry over the last 25 years.

8. Constructional details of c.n.c machines
In general, a cnc machine tool consists of the following units:
(i) Computers
(ii) Control system
(iii) Drive motors
(iv) Tool changers
According to the construction of cnc machine tools, it works in the following (simplified) manner:-
1. The cnc machine controlled by the computer reads the program and translates it into machine language,
which is a programming language of binary notation used on computers, not on cnc machines.
2. When the operator starts the execution cycle, the computer translates the binary codes into electronic pulses
which are automatically sent to the machine’s power units. The control unit compares the number of
pulses sent and received.
3. When the motor receives each pulse, they automatically transform the pulses into rotations that drive the
spindle and lead screw, causing the spindle to rotate and slide or move the table. The part on the milling
machine table or the tool in the lathe turret is driven to a position specified by the program.
Computers:-
Cnc machines introduced in the late 1970s were less dependent on hardware and more dependent on
software. These machines store a program into memory when it is first read in. This facilitates faster
operation when producing number of identical parts, since the program can be recalled from memory
repeatedly without having to read it again. Cnc machines use an on-board computer that allows the
operator to read,

9. analyze and edit programmed instruction, while nc machines require operators to make a new tape to alter
a program. In essence,the computer distinguishes cnc from nc.as with all computers, the cnc machines
computer also works on a binary principle using only two characters,1 and 0 (machine language) for
information processing. When creating the program, the programmer does not care about the machine
language, instead he or she simply uses a list of codes i.e. g&m codes and keys in meaningful
information. Special built-in software compiles the program into machine language and the machine
moves the tools by servomotors. However,the ability to program the machine is dependent on whether
there is a computer in the machine control. Modern cnc machines use 32-bit processors in their computers
to allow fast and accurate processing of information. This results in considerable saving of machining
time.
Control system:-
There are two types of control systems on nc/cnc machines. The overall accuracy of the machine is
determined by the type of control loop used.
Open loop:-the open loop control system does not provide positioning feedback to the control unit. The
movement pulses are sent out by the control unit and are received by a special type of servomotor called a
stepper motor. The stepper motor then proceeds with the next movement command. Since this control
system only counts pulses and cannot identify discrepancies in positioning, the control has no way of
knowing whether the tool has reached the proper location or not. The machine will continue this
inaccuracy until some body finds the error.the open loop control can be used in applications in which
there is no change in load conditions, such as the cnc drilling machine. The advantage of the open loop
control system is that it is less expensive, since it does not require the additional hardware and electronics
needed for positioning feedback. The disadvantage is the difficulty of detecting positioning error.
Closed loop:-in the closed loop control system, the electronic movement pulses are sent from the control
to the servomotor, enabling the motor to rotate with each pulse. The pulses are detected and counted by a
feedback device called a transducer. With each step of movement, a transducer sends a signal back to the
control, which compares the current position of the driven axis with the programmed position. When the
number of pulses sent and received match, the control starts sending out pulses for the next movement.
Closed loop systems are very accurate. Most have an automatic compensation for error, since the
feedback device indicates the error and the control

10. makes the necessary adjustments to bring the slide back to its position. They use ac, dc or hydraulic
servomotors.
Drive motors:-the drive motors control the machine slide movement on cnc equipment.they are classified
into four basic types as follows:-
Stepper motor:-these convert a digital pulse, generated by the microcomputer unit (mcu i.e. machine
control unit) into small step rotation. Stepper motors have a certain number of steps that they can
travel. The number of pulses that the mcu sends to the stepper motor controls the amount of rotation of
the motor. Stepper motors are mostly used in applications where low torque is required. Stepper motors
are used in open loop control system, while ac, dc or hydraulic servomotors are used in closed loop
control systems.
Dc servomotor:- these are variable speed motors that rotate in response to the applied voltage. They are
used to drive a lead screw and gear mechanism. Dc servos provide high torque output than stepper
motors.
Ac servomotor:-these are controlled by varying the voltage frequency to control the speed. They can
develop more power than a dc servo. They are also used to drive a lead screw and gear mechanism.
Fluid servomotor:-it is also a variable speed motor. They are able to produce more power or more speed
in the case of pneumatic motors than electric servomotors. The hydraulic pump provides energy to valves
which are controlled by the mcu.
Tool changers:-most of the time, different cutting tools are used to produce one part of a machine. The
tools have to be replaced quickly for the next machining operation. Owing to this reason, the majority of
cnc machine tools are equipped with automatic tool changers, such as magazines on machining centers
and turrets on turning centers fig. They allow tool changing without the intervention of the operator.
Typically an automatic tool changer grips the tool in the spindle, pulls it out, and replaces it with another
tool.on most machines with automatic tool changers,the turret or magazine can rotate in either forward or
reverse direction. Tool changers may be equipped for either random or sequential tool selection. In
random tool selection, there is no specific pattern of tool selection on the machining centre,when the
program calls for the tool, it isautomatically indexed into waiting position, where

11. it can be retrieved by the tool handling device. On the turning centre, the turret automatically rotates,
bringing tools into position.
In sequential tool selection, the tools must be loaded in the exact order in which they are called for in the
program (fig.). Even if the tools are not in the correct order, the next tool is automatically selected,
whether it is suitable or not for the next machining operation. When it is necessary to use a tool twice, the
operator must load another tool with the same purpose. The advantage of sequential tool selection is that
less time is needed for indexing the tool into the waiting position. The disadvantage is that more time is
needed for setup when switching to a job with a different order of tools. This means that although the
same tools are to be used, they have to be preloaded (rearranged) because of a different order in the
program. This eliminates the time advantage of sequential tool selection, making random tool selection a
standard feature on today’s cnc machine tools.
Cnc coordinate systems
1. for milling:-
In order for the part programmer to plan the sequence of positions and movements of the cutting tool
relative to the work piece, it is necessary to establish a standard axis system by which the relative
positions can be specified. However,to make things easier for the programmer, we adopt the view point
that the work piece is stationary while the drill bit is moved relative to table. Accordingly, the coordinate
system of axes is established with respect to the machine table. Two axes,x and y, are defined in the
plane of the table, as shown in figure. The z axis is perpendicular to this plane and movement in the z
direction is controlled by the vertical motion of the spindle. The positive and negative directions of
motion of tool relative to table along these axes are as shown in figure. Cnc drill presses are classified as
either two- axes

12. or three- axes machines, depending on whether or not they have the capability to control the z axis.
A numerical control milling machine and similar machine tools (boring mill, for example) use an axis
system similar to that of the drill press. However, in addition to the three linear axes, these machines may
possess the capacity to control one or more rotational axes. Three rotational axis axes are defined in cnc:
the, b, and c axis. These axes specify angle about the x, y, and z axes, respectively. To distinguish positive
from negative angular motions, the “right-hand rule” can be used. Using the right hand with the thumb
pointing in the positive linear axis direction (x, y, or z), the fingers of the hand is curled to point in the
positive rotational direction.
2. For turning:-
For turning operations, two axes are normally all that are required to command the movement of the tool
relative to the rotating work piece. The z axis is the axis of rotation of the work part, and x axis defines
the radial location of the cutting tool. This arrangement is illustrated in figure.the purpose of the
coordinate system is to provide a means of locating the tool in relation to the work piece. Depending on
the cnc machine, the part programmer may have several different options available for specifying this
location.
Positioning of machine origin
Fixed zero:- the programmer must determine the position of the tool relative to the origin (zero point) of
the coordinate system. Cnc machines have either of two

13. methods for specifying the zero point. The first possibility is for the machine to have a fixed zero. In this
case,the origin is always located at the some position on the machine table. Usually, that position is the
southwest corner (lower left-hand corner) of the table and all tool locations will be defined by positive x
and y coordinates.
Floating zero:-the second and more common feature on modern cnc machines allows the machine
operator to set the zero point at any position on the machine table. This feature is called floating zero.the
part programmer is the one who decides where the zero point should be located. The decision is based on
part programming convenience. For example, the work part may be symmetrical and the zero point
should be established at the center of symmetry. The location of the zero point is communicated to the
machine operator. At the beginning of the job, the operator moves the tool under manual control to some
“target point” on the table. The target point is some convenient place on the work piece or table for the
operator to position the tool. For example, it might be a predrilled hole in the work piece. The target point
has been referenced to the zero point by the part programmer. In fact, the programmer may have selected
the target point as the zero point for tool positioning. When the tool has been positioned at the target
point, the machine operator presses a “zero” button on the machine tool console, which tells the machine where
the origin is located for subsequent tool movements.
Mode of positioning
Absolute positioning:-

14. Another option sometimes available to the part programmer is to use either an absolute system of tool
positioning or an incremental system. Absolute positioning means that the tool locations are always
defined in relation to the zero point. If a hole is to be drilled at a spot that is 8 in. Above the x axis and 6
in. To the right of the y axis, the coordinate location of the hole would be specified as x=+6.000 and
y=.+8.000.
Incremental positioning :-
Positioning means that the next tool location must be defined with reference to the previous tool location
must be defined with reference to the previous tool location. If in our drilling example, suppose that the
previous hole had been drilled at an absolute position of x=+4.000 and y=+5.000. Accordingly, the
incremental position instructions would be specified as x=+2.000 and y=+3.000 in order to move the drill
to the desired spot.figure illustrates the difference between absolute and incremental positioning.
CNC motion control systems
In order to accomplish the machining process, the cutting tool and work piece must be moved relative to
each other. In cnc, there are three basic types of motion control systems:-

15. 1. Point- to- point cnc:-point-to-point (ptp) is also sometimes called a positioning system. In ptp,
the objective of the machine tool control system is to move the cutting tool to a predefined location. The
speed or path by which this movement is accomplished is not important in point-to-point cnc.
Once the tool reaches the desired location, the machining operation is performed at that position. Cnc drill
presses are a good example of ptp systems. The spindle must first be positioned at a particular location on
the work piece. This is done under ptp control.then the drilling of the hole is performed at the location,
and so forth. Since no cutting is performed between holes, there is no need for controlling the relative
motion of the tool and work piece between whole locations. Figure illustrates the point-to-point type of
control.
2. Straight-cut cnc:- straight-cut control systems are capable of moving the cutting tool parallel to
one of the major axes at a controlled rate suitable for machining. It is therefore appropriate for performing
milling operations to fabricate work pieces of rectangular configurations. With this type of cnc system it
is not possible to combine movements in more than a single axis direction. Therefore, angular cuts on the
work piece would not be possible. An example of a straight-cut operation is shown in figure. A cnc
machine capable of straight cut movements is also capable of ptp movements.
3. Contouring cnc: - contouring is the most complex, the most flexible, and the most expensive type
of machine tool control. It is capable of performing both ptp and straight-cut operations. In addition, the
distinguishing feature of contouring cnc systems is their capacity for simultaneous control of more than
one axis movement of the machine tool. The path of the cutter is continuously controlled to generate the
desired geometry of the work piece. For this reason, contouring systems are also called continuous-path
cnc systems. Straight or plane surfaces at any orientation, circular paths, conical shapes, or most any other
mathematically definable form are possible under contouring control. Figure illustrates the versatility of
continuous path cnc. Milling and turning operations are common examples of the use of contouring
control.
G CODES
CODE FUNCTION
G00 POINT TO POINT POSITIONING MODE OF CONTROL(RAPID
TRANSVERSE)

16. G01 LINEAR INTERPOLATION MODE OF CONTROL(LINEAR TRANSVERSE)
G02 CIRCULAR INTERPOLATION ARC CLOCKWISE(NORMAL DIMENSION)
G03 CIRCULAR INTERPOLATION ARC COUNTER CLOCKWISE(USED FOR
NORMAL DIMENSION)
G04 DWELL-A PREDETERMINED TIME DELAY BEFORE EXECUTING
(CURRENT BLOCK INSTRUCTIONS.)
G05 HOLD-AN INFINITE DELAY BEFORE EXECUTING CURRENT BLOCK
INSTRUCTIONS TERMINATED ONLY BY OPERATOR OR INTERLOCK
SWITCH.
G06 UNASSIGNED-MAY ACQUIRE STANDARD USE.
G07 AVOID ACCELERATION
G08 REACCELERATION
G09 LINEAR INTERPOLATION USED FOR LONG DIMENSIONS
G10 LINEAR INTERPOLATION USED FOR SHORT DIMENSION
G11 3-D-INTERPOLATION
G12 TO
16
AXIS SELECTION
G17 XY PLANE SELECTION
G18 ZX PLANE SELECTION
G19 YZ PLANE SELECTION
G20 CIRCULAR INTERPOLATION ARC CW(INCHES MODE)(USED FOR LONG
DIMENSIONS)
G21 CIRCULAR INTERPOLATION ARC CW FOR (MM) MODE (USED FOR
SHORT DIMENSIONS)
G22 COUPLED MOTION-
G23 COUPLED MOTION-
G24 UNSIGNED
G25 START OF SUB ROUTINE
G26 END OF SUB ROUTINE
G27 TO
29
UNASSIGNED
G30 RESERVED FOR CONTOURING CCW(LONG DISTANCE)
G31 RESERVED FOR CONTOURING CCW (SHORT DISTANCE)
G32 UNASSIGNED
G33 THREAD CUTTING (CONSTANT LEAD)
G34 THREAD CUTTING (INCREASING LEAD)
G35 THREAD CUTTING (DECREASING LEAD)
G36 USED FOR CONTROL PURPOSE ONLY
G37 CALLING OF SUBROUTINE
G38

17. G39 PERMANENTLY UNASSIGNED
G40 CUTTER COMPENSATION (CANCEL)
G41 CUTTER COMPENSATION (LEFT)
G42 CUTTER COMPENSATION (RIGHT)
G43 CUTTER COMPENSATION (POSITIVE)
G44 CUTTER COMPENSATION (NEGATIVE)
G45 TO
51
UNASSIGNED
G52 UNASSIGNED AND RESERVED FOR ADAPTIVE CONTROL
G53 LINEAR SHIFT CAN EL
G54 LINEAR SHIFT (X)
G55 LINEAR SHIFT(Y)
G56 LINEAR SHIFT(Z)
G57 LINEAR SHIFT(XY)
G58 LINEAR SHIFT(XZ)
G59 LINEAR SHIFT(YZ)
G60 TO
61
UNASSIGNED
G62 POSITIONING FAST
G63 TAPPING
G64 CHANGE OF RATE
G65 CASSETTE LOAD
G66 CASSETTE SAVE
G67 CASSETTE SEARCH
G68 TO
69
UNASSIGNED
G70 INCH PROGRAMMING ON CNC TOOLS WHICH ACCEPT DIMENSIONS IN
INCHES AS WELL AS MILLIMETERS

18. G71 METRIC PROGRAMMING
G72 TO
77
UNASSIGNED
G78 MILL CYCLE
G79 MILL CYCLE
G80 FIXED CYCLE CANCEL
G81 REPEAT FUNCTION-FIXED TURNING CYCLE/DRILLING CYCLE.
G82 CIRCULAR CYCLE/DRILL DWELL
G83 DRILLING CYCLE
G84 RECTANGULAR CYCLES(THREADING CYCLE)
G85 TO
89
UNASSIGNED
G90 ABSOLUTE DIMENSION PROGRAMMING
G91 INCREMENTAL DIMENSION PROGRAMMING
G92 POSITION PRESET
G93 UNASSIGNED
G94 FEET RATE IN MM/MIN(INCHES/MM)
G95 FEET RATE IN MM/REV(INCHES/REV)
G96 CONSTANT SURFACE SPEED (MM/MIN)
G97 SPEED (REV/MIN)
G98 SPEED (REV/MIN)
G99 FLOATING DATUM
M CODES
M00 PROGRAM STOP
M01 OPTIONAL (PLANNED) STOP
M02 END OF PROGRAM
M03 SPINDLE START IN CLOCKWISE DIRECTION.
M04 SPINDLE START IN ACW DIRECTION.
M05 SPINDLE STOP
M06 TOOL CHANGE
M07 COOLANT ON (TYPE 2-FLUID COOLING)
M08 COOLANT ON (TYPE 1-MIST COOLING)
M09 COOLANT OFF
M10 CLAMP
M11 UNCLAMP

19. M12 UNASSIGNED
M13 CW SPINDLE START-COOLANT ON
M14 ACW SPINDLE START + COOLANT ON
M15 MOTION + VE
M16 MOTION – VE
M17 UNASSIGNED
M18
M19 ORIENTED SPINDLE STOP
M20 AUXILIARIES.
M21 INPUT
M22 TO
29
UNASSIGNED
M30 END OF TAP, SIMILAR TO M02 EXCEPT THAT IT MUST INCLUDE
REWINDINGOF TAPE TO END OF RECORD,THUS READY FOR NEXT WORK
PIECE.
M31 INTERLOCK BY-PASS
M32 TO
35 CONSTANT CUTTING SPEED (USED WITH TURNING)
M36 FEED RANGE 1
M37 FEED RANGE 2
M38 SPINDLE SPEED RANGE 1
M39 SPINDLE SPEED RANGE 2

20. M40 TO
47
GEAR CHANGE
M48 CANCEL M49
M49 BYPASS OVERRIDE
M50 COOLANT NO.3 ON
M51 COOLANT NO.4 ON
M52 TO
54
UNASSIGNED
M55 LINEAR TOOL SHIFT POSITION 1
M56 LINEAR TOOL SHIFT POSITION 2
M57 TO
59
UNASSIGNED
M60 WORK PIECE CHANGE
M61 LINEAR WORK PIECE SHIFT POSITION 1
M62 LINEAR WORK PIECE SHIFT POSITION 2
M63 TO
67
UNASSIGNED
M68 CLAMP WORK PIECE
M69 UNCLAMP WORK PIECE
M70 UNASSIGNED
M71 ANGULAR WORK PIECE SHIFT POSITION 1
M72 ANGULAR WORK PIECE SHIFT POSITION 2
M73 TO
77
UNASSIGNED
M78 CLAMP SLIDE
M79 UNCLAMP SLIDE
M80 TO
89
UNASSIGNED

21. STOCK DEFINATION
l - Stock length
d1 - cylinder diameter
d2 - hole diameter
z - Origin z
The stock reference point (origin) is the center of the right face. Origin z indicates the z position of the
program origin relative to the stock origin.
If the stock has more complicated shape than cylinder it may be defined by sequence of g-code lines
prefixed with the character your cnc controller uses for a comment line. This sequence must be placed
between stock/begin and stock/end commands.
TOOL DEFINITIONS.
Standard od tool:
TOOL/STANDARD, BA, A, R, IC, ITP
Standard id tool has the same definition (back angle instruct cut viewer to the orientation of the tool):

22. Note: the ic (inside circle) is the diameter for which the tool insert geometry is created about. The IC is an
industry standard term used by all insert manufactures. The itp (imaginary tool point) is the intersection of
the vertical and horizontal edges of the tool and this point often is used for tool path programming.

23. the itp is a value indicating the tip position of the imaginary tool point with respect to the tool nose radius
center point as illustrated below.
It p=0 if the tool nose radius center point is used for tool path programming.
Grooving od tool:
Tool/groove, r1, r2, l, w, a1, a2, oa, itp
Oa=90
Grooving id tool:
Tool/groove, r1, r2, l, w, a1, a2, oa, itp
Oa=270

24. For face tool oa=0
Note: to change control point (left or right tool corner) simply changes sign of w value.
Threading od tool:
tool/thread, a, l, w, oa
Drill:
Tool/drill, d, a, l

25. PART PROGRAMMING
the programmer carefully converts the sequence of operations to a set of instructions, i.e., (part
program). Part programming consists of sequence of blocks. each block has a specific function to
perform. Machine read one block & commands the tool or other slides to perform that operation. After
this controller shifts to the next block. in this way complete machining is performed which consists of
small step operation define by each block. let us take example of some blocks.
Format: g02 x__ z__ i__ k__ f__( i, k format)
Or g02 x__ z__ r__ f__
Here in first syntax,
i = distance between start point & center point of arc along x-axis.
k= distance between start point & center point of arc along z-axis.
& in second syntax
r = radius of the arc.
The g02 command is utilized to move the tool in the circular arc profile. with g02 the movement will be
in the clockwise direction. the movement taken will be at the programmed feed rate.
Manual part program:-
the program contains g and m codes. g codes are called preparatory codes. they prepare the machine for
cutting operation e.g. linear interpolation, circular interpolation, rapid etc. m codes are called
miscellaneous codes.they perform all other operation except for cutting like spindle on/off, coolant on/off,
tools changing etc.the manual part program looks like the following statement.
n10 g90 g00 x + 100 y – 100 z + 50; (single block)
Programming tips
programming is just like any other work- with good knowledge and appositive attitude; it can be done
right and with first class results. here are some tips to get the best
result from any programming effort.

26. 1. Approach cnc programming in a logical and methodological way.
2. always calculate unknown values – never guess.
3. Standardize a programming style and adhere to it.
4. program dimensional values in absolute mode whenever possible.
5. make a setup sheet and/or tooling sheet before programming, not after.
6. Program as many machining operations in a single setup as possible.
7. Use minimum numbers of tools for maximum number of jobs- standardize.
8. always program for the safety of cnc machining.
9. document your work and store everything relating to the program development.
10. watch for programming errors- syntax and logical- all errors are avoidable.
Advantages of CNC machine
Most of the advantages derived from cnc technology are due to the high level of automation, high
flexibility of cnc machines and their ability to combine multifunction machining requirements in
minimum number of workstations and setups.
The significant advantages are as follows:
High accuracy and repeatability:
reduced inspection:
 ease of assembly and interchangeability.
 less scrap and rework
 Reduction in floor space/number of men/handling, results in better management control over the
production.
 Development of new work is done faster with the usage of cnc machines.
 saving in jigs and fixtures as well as in dead time;
 less material handling.
 Cost accounting and production control becomes very precise.
 Dependence on skilled operators can be dispensed with.
 Optimum utilization of horse power of the machine.
 increase effective machine utilization:
 reduced usage of tools.
 less paper work.

27. CHAPTER-2
NUMERICAL CONTROL (NC) AND COMPUTER NUMERICAL
CONTROL (CNC)
Numerical control refers to the operation of machine tools from numerical data. Data for the operations
may be stored on paper tape, magnetic tape, magnetic disks, etc. because numerical information is used,
the concept is called numerical control. Numerical control is the operation of machine tools and other
processing machines by a series of coded instructions. with a built-in computer controlling the machine
tool functions and the system is known as computer numerical control (cnc).
A typical numerical control machine tool system contains three basic
components:
1. A program, that is, a set of instructions
2. A machine control unit (mcu)
3. The machine tool.
figure shows these three basic components.

28. Fig-1-basic components of nc machine in the nc system, all the information which is required for
producing a component, viz. dimensional information. Speed, feed, and cutting speed is stored in the
coded form as a part program.
the mcu is further divided into two elements: the data processing unit (dpu) and
control loops unit (clu). the dpu processes the coded data read from the tape or other storage media and
passes information on (i) the position of each axis, (ii) required direction of motion, (iii) speed, feed, and
(iv) auxiliary function control signals to clu. For example, a typical part program may contain an
instruction
x + 100, y + 50, s + 90
this instruction is interpreted as: to move by a distance of 100 mm in the x-positive direction, 50 mm in
the y-positive direction and rotate the spindle at 90 rpm clockwise. these information pieces are decoded
by the dpu and sent to clu.
the clu operates the drive mechanisms of the machine to move the table in x and y directions, and to rotate
the spindle as specified. then it receives feedback signals concerning the actual position and velocity of
each of the axes, and signals for completion of the operation. when execution of one line (instruction) as
noted by the clu is complete, another instruction is read. a data processing unit consists of some or all of
the following parts:
• Data input device such as a paper tape reader,magnetic tape reader,etc.
• Data reading circuits and parity checking logic
• decoding circuits for distributing data among the controlled axes
• An interpolator, which supplies machine-motion commands between data points for tool motion.
• A control loops unit, on the other hand, consists of the following:
• Position control loops for all the axes of motion, where each axis has a separate control loop
• Velocity control loops, where feedback control is required
• Deceleration and backlash take up circuits
• Auxiliary functions control, such as coolant on/off, gear changes, spindle on/off control.
Geometric and kinematics data are fed from the dpu to the clu. the clu then governs the physical system
based on the data received from the dpu.
Processing equipment is the third basic component of the nc system.
it is the machine tool that performs the useful work. the machine tool is designed or modified to be
controlled, operated, and interfaced with the control loop unit (clu).

29. Advantages of NC system
NC systems offer several advantages over the conventional manufacturing methods. These are:
1. High machine utilization
2. Need for special tooling is mostly eliminated
3. High quality products can be manufactured
4. Consistency in quality
5. Quality is not dependent on the operator's skill
6. Lesser production cost per unit
7. Reduced scrap
8. Reduced in-process inventory
9. Higher productivity
10. Reduced set-up time.
Disadvantages of NC system
1. Very high initial investment on specialized equipment
2. Redundancy of labour
3. Downtime of NC is highly expensive
4. Special skill is required for programming and operating equipment.
Comparison between CONVENTIONAL MACHINES and NC
MACHINES
1. The NC machine differs from a conventional machine in many ways. Different aspects of the two are
compared here.
2. New NC machines cost around two to five times more than the similar capacity conventional
machines,
depending upon the sophistication of the control system and the size of the machine.
3. Conventional machines require a high order of skill and trained personnel to operate to produce
complex
Contours.
4. The machine hour rate is generally higher for the NC machines or the down time of these machines is
Very costly.
5. Maintenance of NC machine is costlier than the conventional machine.
6. The production rate of NC machines is higher than that of the conventional machines and they can
produce complicated profiles consistently with good accuracy.

30. 7. NC machines require special tooling. Because, these machines are designed to operate at the very high
Operating conditions (today, NC machines are capable of operating at 50,000 rpm) Tools made from
Carbon tool steel and HSS cannot be used at such a high speed.
8. Use of automatic tool changers to change the tool automatically and simultaneous machining by
multiple
tools are the features available with high-end NC machines. These features help to reduce down
time set-up time.
Coordinate systems and Program Zero Point
To describe the geometry of a workpiece for NC programming, we use coordinate systems with X-, Y- and Z-axes. The origin of
the frame and the alignment of the axes are chosen in such a way that any point on the workpiece can be defined by naming its X,
Y and Z coordinate values. A coordinate frame attached to the corner of a prism is shown in Fig.2. The directions of X, Y, Z axes
illustrated in Fig. 2 are treated as the positive directions and the movement of the tool in the opposite direction is treated as
negative.
Lathe coordinate system
Milling machine coordinate system

31. the point of intersection of the three axes (the origin) is called zero point. A point at a distance 60 mm
from the zero point in positive X direction and 30 mm in positive Y direction is denoted as:
X + 60, Y + 30
And a point 10 mm below the top surface at the above location is denoted as:
X + 60, Y + 30, Z - 10
It is also possible that we can locate the origin of another coordinate frame anywhere in the work piece.
This new origin of frame is called program zero point. All coordinate values in the program may be
referred relative to the program zero point. The different locations of program zero point are illustrated in
Fig. 3

32. With a program zero point at the lower left corner of a workpiece, the coordinate

33. With a program zero point at the lower left corner of a workpiece, the coordinate values of X + 50, Y +
60, Z + 30, for example, would mean that the tool is required to move to a point located 50 mm away
from the program zero point in positive X direction, 60 mm away in positive Y direction and 30 mm
away in positive Z direction. This is shown in Fig.4
DEFINING THE COORDINATE SYSTEM FOR A TANGENT POINT P
Classification of Numerical Control Machines.
Numerical control machines can be generally classified using the following categories:
1. Type of motion
2. Programming method
3. Control system.
Type of motion
According to the type of motion, NC machines can be classified as:
1. Point-to-point systems
2. Contouring or continuous systems.

34. Point-to-point systems.
In case of point-to-point (PTP) motion machine tool, the cutting tool moves to a numerically defined
location, the motion is stopped and the task is performed. After completing the task, the tool moves to the
next point and the cycle is repeated. In a PTP system, the path of movement of the tool and its velocity,
when the tool moves from one point to another, is of no significance.
Contouring or continuous systems. The tool has to move in a predetermined path in the case of contouring or continuous
systems. For example, consider the component ABCD, as shown in Fig. 5 (b), to be cut from the material.
To manufacture this component, the tool has to move in a predefined contour (path) A-B-C-D. The
intermediate points of the contour are obtained by interpolator, which is contained in DPU of the
processing systems. That is, while moving from A to B (or B to A) in Fig. 5 (b) we just need to input the
coordinates of points A and B, then define whether these points A and B are joined by a straight line or an
arc then interpolator automatically calculates all the intermediate points between A and B and accordingly
gives the signal such that the tool is moved in the respective path
Programming method
According to programming method used, NC system can be classified into two categories as:
1. Absolute positioning
2. Incrementalpositioning (or Chain positioning).
Absolute Positioning.
In absolute positioning, the coordinates of the target point are defined with respect to a fixed program
zero point. Absolute dimensions tell the control to what point the tool is to move, regardless of its current
position. Figure 6 shows absolute positioning for point B, irrespective of whether the tool was at A or at
C. It can be observed from Fig. 6 that all the values are based on the program zero point. The positional
command for the tool to reach point B would be X + 70, Y + 30

35. Incremental positioning.
Incremental or chain positioning tells the control by what amount the tool is to move from its present
position. The present position of the tool acts as the program zero point. Chain positioning for point B
from point A and from point C are shown in Figs. 7 and 7(b), respectively.
Each coordinate value is based on the end point of the previous location. The positional command for the
tool to reach B from A would be X + 50, Y + 20 and to reach B from C would be X + 30, Y - 10

36. Control System
According to the typeof controlsystems used, NC systems can be classified as:
1. Open loop system
2. Closed loop system.
Every control system, including NC systems may be designed as open loop or closed loop control.
Open loop system:
The term open loop means that there is no feedback,and the action of the controller has no information
about the effect of the signal that it produces. Figure 8 shows an open loop control for a single axis of
motion.
Since there is no feedback information, the system accuracy is solely a function of the motor's ability to
pass through the exact number of steps, which is provided at its input.

37. Closedloop system:
In a closed loop control system, the actual position and the velocity of the axis are measured with sensors.
The schematic diagram of the closed loop system is shown in Fig. 9. Assuming a digital control system, a
digital to analogue convertor (DAC) is included in Fig. 9
CLOSED LOOP CONTROL SYSTEM
The difference between actualand the programmed value is termed as the- error. The control system is
designed in such a way so as to eliminate the error or reduce it to a minimum.
Advantages of CNC Systems over Conventional NC Systems
 Because the computer can be readily and easily reprogrammed, therefore, the system is very flexible. The
machine can manufacture a part followed by other parts of different designs.

38.  More versatility. Editing and debugging programs, reprogramming and plotting and printing part shapes
are simpler
 Program to manufacture a component can be easily called. This saves time and eliminates errors Due to
tape readin
 Greater accuracy.
What is CNC wood router?
A CNC wood router is a Numerical control tool that creates objects from wood. Parts of a object can be
made and then assembled using a router to produce a complete object.
The CNC router works like a printer. Work is composed on a computer and then the design or drawing is
sent to the CNC router for the hard copy. This outputs a 3-dimensional copy of the work. The CNC router
uses a cutting tool instead of an ink jet. The cutting tool is generally a router but other cutters can be used
as well.
A CNC wood router uses CNC (computer numerical control) and is similar to a metal CNC mill with the
following differences:
• The wood router typically spins faster — with a range of 13,000 to 24,000 RPM
• Low end hobby grade machines typically uses smaller tools — typical shank size 20 mm or at most 25
mm. Professional quality machines frequently use surface facing tools up to 3" in diameter or more, and
spindle power exceeding 15 horsepower.

39. CHAPTER-3
APPLICATIONS
CABINETS - Making cabinet components on a CNC router has become a common practice today. The
technology of manufacturing cabinet boxes, doors, drawer fronts, shelves and even countertops with a
robotic tool is now well within the reach of smaller shops. Using CNC technology, cabinetmakers are
now able to increase production throughput, while minimizing material handling.
WOODWORKING - In addition to high-volume furniture and millwork companies, novice and master
craftsmen alike are embracing CNC technology in their workshops.
SIGNS – CNC Wood routers are used in signmaking to carve images in wood and foam, to cut plastic
and aluminum letters, and to intricately machine the all sorts of graphic objects and letters. Full 3D
cutting capabilities allow cutting and machining of practically anything.
BOATS - Boatbuilding is a natural for utilizing the benefits of CNC technology, In boatbuilding, CNC
Wood routers are used for cutting frames, plywood panels and all manner of interior and exterior parts.
They are used in wood, fiberglass and aluminum production processes.
INSTRUMENTS - Luthiers of all disciplines can now supplement their traditional woodworking tools
with CNC routers. While the CNC may not duplicate all of the specialized processes involved in
instrument making, it brings new capabilities that can transform an ordinary shop to an extraordinary one.

40. CHAPTER-4
REFERENCES
1. www.wikipedia.org/wiki/Main
2. www.bhel.com/home.php
3. Electrical and electronic Instrumentation by A.K. Shawney.
4. http://www.yourpersonalplctutorsite.htm
5. http://www.pc-control.co.uk/index.htm.
6. http://www.plcmanualbasicguidetoplc.htm
8.http://www.sea.siemens.com/step/templates/lesson.mason?plcs:1:1:1
.