CNC%20Programming

8/8/2019 CNC%20Programming

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Symbols of good program.

Easily understood .

Minimum air cutting.

Avoid repetition of tools.

Should be simple and short.

Considered future tooling changesfeasibility.

Should not hamper m/c tool life.


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Contents What is mean by CNC program ?

Coordinate measuring systems. Dimensioning system.

CNC programming formats.

G-CODES (Preparatory functions.)

M-CODES (Miscellaneous Functions)

Canned Cycles.

Subprogram/Subroutine.

Preparation required before doing program.

Example of one program.

Precautionary measures while doing and executing

CNC Program.


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CNC program

Set of instructions fed to the machine

control in the form of numerical codes

written in particular sequence.


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Example of CNC program.

N10/ (Core drill dia 55)

N20 T1 M6 ;

N30 G0 G90 G54 X200. Y150. ;

N40 G0 G43 H01 Z100. ;

N50 G98 G81 Z-25 R5 F40 ;N60 G80 G91G28 X0. Y0. Z0. ;


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System of coordinates.

It is used in preparation of part program forintroducing the position of machining.

It consists of 3 axis ( X,Y&Z)

There are two types of system of

coordinates.

M/C coordinate system (G53).

Workpiece coordinate system (G54-G59).


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System of coordinates.M/C coordinate system.

M/c actually moves in its own system of

coordinates called M/C COORDINATE

SYSTM.and reference point w.r.t.which it

moves called as M/C ZERO

Generally m/c coordinate system has

machining zone on -ve direction from m/czero point.


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System of coordinates.M/C coordinate system.


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System of coordinates.W/P coordinate system.

To make machining easy temporary

reference point is taken in m/c coordinate

system this point is called as WORKZERO.

Distances of this temp. point in X,Y&Z

direction from m/c zero called as ZEROOFFSET


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Generally this point should be such that all

dimensions on part drawing would be from

that point.

For e.g. Locating pin center.


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System of dimensioning

G90 (Absolute Dimensioning)

It is the most common method of dimensioning

our drawings used for part production on CNCmachines.

In this system all dimensions are taken from a

single point called as DATUM POINT orORIGIN.

This is denoted by preparatory function G90.


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G90 (Absolute Dimensioning)

ADVANTAGES:

If hole no. 2 is put inwrong location hole no.3

would not be affected.

Generally our drawingsare dimensioned in

absolute method so it

becomes very to find out

the co-ordinates .

50.0

100.0

150.0

150.0

50.0

100.0

1

2

3


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G91 (Incremental Dimensioning)

It is very rarely used.

Generally it is used for machining ofcomplicated pockets.

In this system measurement is from hole to hole

This is denoted by preparatory function G90.


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System of dimensioningG91 (Incremental Dimensioning)

If hole no. 2 is put in

wrong location next all

holes will be incorrectly

positioned.

For doing programming in

incremental mode

tremendous calculationsare required.

It benefits while doing

subprograms

50.0

1

2

3

50.0

50.0

50.0 50.0 50.0


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System of dimensioningExample of G90 & G91

G90

N10 G71 ;

N20 G90 ;N30 G00 X100. Y100. ;

N40 X150. Y100. ;

N50 X150. Y150. ;N60 X100. Y150. ;

N70 X100. Y100. ;

N80 M30

100.0

150.0

100.0

150.0

X

Y


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Program format

Format is method of writing set of instructions.

N10 G01 X10. Y10. F200 S200 T01 M3 ;

SEQUENCE

NO.

PREPARATOTYFUNCTION

X-COORDINATE

Y COORDINATE

FEED FUNCTION

SPEED FUNCTION

TOOL FUNCTION

MISCLLANEOUS FUNCTION

END OF BLOCK


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G codes

G-Codes are also called as Preparatoryfunctions as they take active part in part

program execution.

They are always programmed at the start ofblock.

They decides type of machine movement

,type of interpolation,type of dimension etc.


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Modal : Which remain active until another Gcode of same group is programmed.Blockwise active : Gcode which remainactive only in that particular block in which itis programmed.

Modal Blockwise active.

G codes

Type of G codes


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G00 (Rapid positioning)

Position data command programmed after

G00 is traversed at maximum possible

feedrate along a straight line set by machine

tool manufacturer.

G00 can be programmed as G or G0.

G00 is modal and canceled with G01 or

G02 or G03.

On graphic screen G00 appears as a dotted

line.


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G00 (Rapid positioning)

Example :

15 60

(0,0)

+Y

-Y

+X-X

1

2

20

To move from point 1 to point 2 command data is given as

G00 X75 Y-20 ;


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G01 (Linear interpolation)

Position data command programmed after G01is executed at programmed feedrate along a

straight line.

Movement being made along straight linejoining start point and end point.

G01 is modal and canceled with G00 , G02 or

G03. On graphic screen G01 appears as continuos

line.


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G01(Linear interpolation).

Example :

15 60

(0,0)

+Y

-Y

+X-X

1

2

20

To move from point 1 to point 2 command data is given as

G01 X75 Y-20 F20 ;

End of block

Programmed feed rate

Position data

Movement at set feedrate.


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G02/G03 (Circular interpolation)

Position data given after G02 or G03 is

executed along a circular path at the set feed

rate.

The code G02 refers to the circular

interpolation in a clockwise direction.

The code G03 refers to the circularinterpolation in a Anticlockwise direction.


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G02/G03 (Circular interpolation)

When we write code G02 ,We have to feed

information regarding

-Start point-End point

-Radius of arc or Circle center point.


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Example of G02/G03 with radius.

G02

N10 G01 X40. Y40. ;

N20 G02 X80. Y80. R40 ;

G03

N10 G01 X80. Y80. ;

N20 G03 X40. Y40. R40 ;

(40,40)

(80,80) (80,80)

(40,40)

GO2

G03


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G02/G03 - Circular interpolation

with circle center point

Here instead of giving radius of circle we have

to mention center point of circle in form of

parameters called I,J&K.

Where I --- Distance between starting point of

cutter to the center of arc in X direction.

J--- Distance between starting point of cutter to

the center of arc in Y direction.

K --- Distance between starting point of cutter

to the center of arc in Z direction.

Values of I,J&K are always incremental.


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Example of G02/G03 with

interpolation parameters..

G02N10 G01 X40. Y40. ;

N20 G02 X80. Y80. I40 J0 ;(40,40)

(80,80)

GO2


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G04 (Dwell)

It is used to program dwell time in sec. Dwell time value is programmed by means

of letter X.

For e.g. N10 G04 X2 ;Means spindle will take dwell of 2 sec. While

executing this line.

It is blockwise active. No other function can be programmed in a

block in which G04 is programmed.


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Cutter radius compensation

To accommodate difference in programmed

diameter of cutter and actual diameter of

cutter ,cutter compensation concept is used.

While writing part program it is necessary

to mention that whether cuttercompensation is required in left direction or

right direction.


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Following 3 G-codes are used for cutterradius compensation.

G41 Compensation applied to shift the cutter

path to left.G42 Compensation applied to shift the cutter

path to right.

G40 To cancel cutter Compensation.

Direction of shift is decided by looking in

direction of cut.


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Advantages :

1.Different dia. of cutters can be used without

changing part program.

2.By using cutter radius compensation job of

programmer becomes simplified because part

program can be developed assuming zero cutter

radius and on actual dimensions of part

drawing.


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G41/G42

G41G42

Cutter

center

line

Cutter

center

line


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Example

35.0

35.080.0

95.0

X

R15.0


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G70 (Inch unit system)

It is used to represent inch unit system

for e.g. N10 G70 G0 X4. ;

It indicates that X axis will move by 4.

For e.g N10 G70 G95 F0.02 ;

It indicates that tool will move at the feed rate

of 0.02 inch/rev

This is an modal G code.


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G71 (Metric unit system)

It is used to represent metric unit system

for e.g. N10 G71 G0 X4. ;

It indicates that X axis will move by 4mm.

For e.g N10 G71 G95 F0.02 ;

It indicates that tool will move at the feed rate

of 0.02 mm/rev



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G94 (feed /min)

When code G94 is programmed CNC

assumes that feed rate value entered under

address F is in mm/min or inch/min.

for e.g. N10 G94 F100 ;

It means that tool moves at the rate of

100mm/min or 100 inch/min depends uponG70/G71.



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G95 (feed /rev)

When code G95 is programmed CNC

assumes that feed rate value entered under

address F is in mm/rev or inch/rev.

for e.g. N10 G94 F0.2 ;

It means that tool moves at the rate of 0.2

mm/rev or inch/rev depends upon G70/G71.



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MISCLLANEOUS FUNCTIONS

(M CODES) :

Miscellaneous function word is used to

specify certain miscellaneous functions

which do not relate to dimensionalmovements of the machine.

For e.g. Spindle start , Spindle stop etc.


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Canned cycle :

Canned cycle or fixed cycle may be defined

as a set of instructions inbuilt or stored in

the system memory to perform fixedsequence of operations.

Canned cycle can be brought into actionwith single command and as such reduce

programming time and efforts.


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Canned cycle :

Canned cycles are used for repetitive and

commonly used machining operations .

Canned cycles are stored under G code address.

G81 to G89 are reserved for canned cycles andG80 for cancellation of canned cycle.


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Drilling cycle (G81) :

POINT R

POINT 'Z'

INITIAL LEVEL

POINT 'Z'

POINT R

G81(G98) G81(G99)

POINT 'R' LEVELw/p

w/p


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Format for Drilling cycle (G81) :

X_ Y_ Hole position data.

Z_ Distance from point R to the bottom of hole.

R_ Distance from initial level to point R level.

F_ Cutting feed rate.

K_ No. of repeats.

Format : G81 X_ Y_ Z_ R_ F_ K_


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Operation sequence for Drilling

cycle (G81) :

Tool is positioned to X&Y axes.

Rapid traverse is performed upto point R. Drilling is performed from point R to point Z.

Tool is then retracted in rapid traverse upto

point R or upto point Z depends uponG98/G99.


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Drilling cycle (G81) :

IMPORTANT POINTS :1.Before specifying G81 use a miscellaneous

function (M CODE) to rotate the spindle.

2.Specify R in block that perform drilling .If it isspecified in block that does not performeddrilling it can be stored as MODAL data.

3. In canned cycle mode tool offsets are ignored.4.Do not specify G codes from G00 To G03

together with G81 otherwise G81 is canceled.


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Counter boring cycle (G82) :

POINT R

POINT 'Z'

INITIAL LEVEL

POINT 'Z'

POINT R POINT 'R' LEVELw/p

w/p

P P

G82(G98) G82(G99)

F f C b i l (G82)


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Format for Counter boring cycle (G82) :




P_ Dwell time at the bottom of hole.


K_ No. of repeats.

Format : G82 X_ Y_ Z_ R_ P_ F_ K_


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Operation sequence for counter

boring cycle (G82) :



Tool remains idle at the bottom over the period

mentioned in P. Tool is then retracted in rapid traverse upto

point R or upto point Z depends upon

G98/G99.



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IMPORTANT POINTS :1.Before specifying G81 use a miscellaneous function

(M CODE) to rotate the spindle.

2.Specify R in block that perform drilling .If it isspecified in block that does not performed drilling it

can be stored as MODAL data.

3. In canned cycle mode tool offsets are ignored.4.Do not specify G codes from G00 To G03 together

with G81 otherwise G81 is canceled.

P k d illi l (G83)


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Peck drilling cycle (G83) :

w/p

R

Z=0

q

d

d

Initial level

R

d

d

q

Z=0

Initial level

G83(G98) G83(G99)

F f P k d illi l (G83)


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Format for Peck drilling cycle (G83) :




Q_ Every cut in value.


K_ No. of repeats.

Format : G83 X_ Y_ Z_ Q_ R_ F_ K_


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Operation sequence for peck drilling

cycle (G83) :






G98/G99.



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Tapping cycle (G84) :

POINT R

POINT 'Z'

INITIAL LEVEL

POINT 'Z'

POINT R

G84(G98) G84(G99)

POINT 'R' LEVELw/p

w/p

p Pspindleccw

spindleccw

spindlecw

spindlecw

F t f t i l (G84)


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Format for tapping cycle (G84) :






K_ No. of repeats.



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Operation sequence for tapping

cycle (G84) :






G98/G99.


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Tapping cycle (G84) :







B i l (G85)


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Boring cycle (G85) :

POINT R

POINT 'Z'

INITIAL LEVEL

POINT 'Z'


w/p

G85(G98) G85(G99)

Format for boring cycle (G85) :


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K_ No. of repeats.



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Operation sequence for boring cycle

(G85) :






G98/G99.



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POINT R

POINT 'Z'

INITIAL LEVEL

POINT 'Z'


w/p

spindlestop

spindlestop

spindlecw

spindlecw

G86(G98) G86(G99)



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K_ No. of repeats.



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(G86) :






G98/G99.



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B k b i l (G87)


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Back boring cycle (G87) :

G87(G98) G87(G99)

NOT USEDPOINT R

spindle cw

spindle cw

P

q

Format for back boring cycle (G87) :


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Format for back boring cycle (G87) :






K_ No. of repeats.



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Operation sequence for back boring

cycle (G87) :






G98/G99.


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POINT R

POINT 'Z'

INITIAL LEVEL

POINT 'Z'


w/p

spindlestop

p

spindle

stopp

spindlecw

spindlecw

G88(G98) G88(G99)



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K_ No. of repeats.



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(G88) :






G98/G99.



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g y ( )









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POINT R

POINT 'Z'

INITIAL LEVEL

POINT 'Z'

POINT R

G89(G98) G89(G99)

POINT 'R' LEVELw/p

w/p

P P



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Z_ Distance from point R to the bottom of hole. R_ Distance from initial level to point R level.



K_ No. of repeats.



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(G89) :






G98/G99.



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g y ( )







CANNED CYCLE SUMMARY


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CANNED CYCLE SUMMARYCANNED CYCLE SUMMARY

CODE Drilling

(- Zdirection)

Operatio

n at thebottom of

hole

Retractio

n(+ Z

direction)

Application

G73 Intermittentfeed

--- Rapidtraverse

High speedpeck drillingcycle.

G74 feed Spindle cw feed Left handtapping cycle.

G76 feed Orientedspindle

stop

Rapidtraverse

Fine boringcycle

G81 feed --- Rapidtraverse

Drilling cycle

G82 feed dwell Rapidtraverse

Counter boringcycle

G83 Intermittentfeed

--- Rapidtraverse

Peck drillingcycle.

G84 feed Spindleccw

feed Tapping cycle

G85 feed --- feed Boring cycle

G86 feed Spindlestop

Rapidtraverse

Boring cycle

G87 feed Spindlestop

Manual/Rapidtraverse

Back boringcycle

G88 feed Dwell-Spindlestop

Manual/Rapidtraverse

Boring cycle

G89 feed Dwell-Spindle

stop

feed Boring cycle

SUBROUTINES


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U U

Also called as SUBPROGRAM.

These are powerful time saving technique.

Subroutines provides the capability of

programming certain fixed sequence or

frequently repeated patterns. Subroutines are in fact independent

programs with all feature of usual part

program. Subroutines are stored in memory under

separate program no.

SUBROUTINES


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Whenever particular feature is required

within the program, associated subroutine iscalled for execution.

Subroutine may called any time and any

no.of times. After execution of subroutine the control

returns to main program .

To describe and use a subroutine followinginformation is required in form of code and

symbol.

SUBROUTINES


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For e.g.

Start of subroutine.End of subroutine.

A means of calling subroutine.

For start we will use letter L followed by any

no. for e.g. L001

For end we will use a word as M17.

For calling subroutine any where in main

program by giving just subroutine no. preceded

by letter L.

E l f b ti


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Example of subroutine.

N10 G91 ;

N20 G01 Z-8. F300 ;

N30 G01 X40. ;

N40 G01 Y40. ;

N50 G01 X-40. ;

N60 G01 Y-40. ;

N70 G00 Z8. ;N80 G90 ;

N90 M17 ;

X

Y

50.0

50.0

90.0

90.0

50.0

(120,120)

(200,200)

Introducing subroutine in main


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program

N10 G90 G71 G94 S500 M03 ;

N20 G00 X50. Y50. ;

N30 G00 Z5 M08 ;

N40 L101 ;

N50 G00 X120. Y120. ;

N60 L101;

N70 G00 X200. Y200. ;N80 L101 ;

N90 G00 X0. Y0. Z20. M09

N100 M30 ;

X

Y

50.0

50.0

90.0

90.0

50.0

(120,120)

(200,200)

What programmer has to do ?


88/96

p g

Study the drawing thoroughly.

Identify type of material to be machined.

Know the specification and functions of

machine to be used.

Decide the dimension mode (mm or inches)

Decide the coordinate system .

Identify the plane of cutting. Know the cutting parameters for job/tool

combinations.

What programmer has to do ?


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p g

Know the federate programming.

Check required toolings.

Establish sequence of machining operations.

Identify whether use of any special feature

like subroutines is required or not.


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Part Program Example.

OPERATIONS TOOLS

Bore dia 60H7 Core Drill dia 55

B. Bar dia 59.5

B. Bar dia 60

Drilling dia 10 HSS Drill dia 10

Tapping M12X1.75 HSS Drill dia 10.8

Tap M12 STD.

Tapping M10X1.5 HSS Drill dia 8.5

Tap M10 STD.



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g p

N10/ (Core drill dia 55)

N20 T1 M6 ;

N30 G0 G90 G54 X200. Y150. ;

N40 G0 G43 H01 Z100. ;N50 G98 G81 Z-25 R5 F40 ;

N60 G80 G91G28 X0. Y0. Z0. ;

N70/ (Semifinish Boring bar dia

59.5)N80 T2 M6 ;

N90 G0 G90 G54 X200. Y150. ;

N100 G0 G43 H02 Z100. ;

N110 G98 G85 Z-25 R5 F40 ;

N120 G80 G91G28 X0. Y0. Z0. ;



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g p

N130/ (Finish bore dia 60)

N140 T3 M6 ;

N150 G0 G90 G54 X200. Y150. ;

N160 G0 G43 H03 Z100. ;

N170 G98 G76 Z-25 R5 Q0.5 F40 ;

N180 G80 G91G28 X0. Y0. Z0. ;

N190/ (Drilling dia 10)

N200 T4 M6 ;

N210 G0 G90 G54 X100. Y255. ;

N220 G0 G43 H04 Z100. ;

N230 G99 G81 Z-25 R5 F40 ;

N240 G98 X275. Y50. ;

N250 G80 G91 G28 X0. Y0. Z0. ;



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g p

N260/ (Drill dia 10.25 for M12tapping)

N270 T5 M6 ;

N280 G0 G90 G54 X380. Y255. ;

N290 G0 G43 H05 Z100. ;

N300 G98 G81 Z-25 R5 F40 ;N310 G80 G91G28 X0. Y0. Z0. ;

N320/ (Tap M12)

N330 T6 M6 ;

N340 G0 G90 G94 G54 X380. Y255. ;

N350 G0 G43 H06 Z100. ;

N360 M29 S100

N370 G98 G84 Z-25 R5 F175 ;

N380 G80 G91 G28 X0. Y0. Z0. ;

Part Program Example


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g p

N390/ (Drill dia 8.5 for M10

tapping)

N400 T7 M6 ;

N410 G0 G90 G54 X150. Y150. ;

N420 G0 G43 H07 Z100. ;

N430 G99 G81 Z-25 R5 F40 ;

N440 X250. ;

N450 X200. Y200. ;

N460 G98 Y100. ;N470 G80 G91G28 X0. Y0. Z0. ;

Part Program Example


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g p

N480/ (Tap M10)

N490 T8 M6 ;

N500 G0 G90 G94 G54 X150. Y150. ;

N510 G0 G43 H08 Z100. ;

N520 M29 S100

N530 G99 G84 Z-25 R5 F150 ;

N540 X250. ;

N550 X200. Y200. ;

N560 G98 Y100. ;N570 G80 G91 G28 X0. Y0. Z0. ;

Precautions while doing or


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executing CNC PROGRAM.

Always add point ( . ) at the end of each

coordinate value of axes.

For e.g. X200. , Y 50. While replacing any tool from m/c check

always tool offset and feed correctly.

Always run first program in single blockand without component.

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