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IE433 CAD/CAM

Computer Aided Designand Computer Aided

Manufacturing

Part-9

CNC Fundamentals


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CNCFundamentals


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All CNC machine tools follow the same standard for

motion nomenclatureand the same coordinate system

!his is defined as the EIA "#$-Cstandard !he standard

defines a machine coordinate system and machinemo%ements so that a &ro'rammer can descri(e

machinin' o&erations without worryin' a(out whether

a tool a&&roaches a wor)&iece or a wor)&iece

a&&roaches a tool


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Machine coordinate system

!he direction of each fin'er

re&resents the &ositi%e direction

of motion

!he a*is of the main s&indle is

always +, and the &ositi%e

direction is into the s&indle

n a mill the lon'est tra%el slide

is desi'nated the . a*is and is

always &er&endicular to the +

a*is

If you rotate your hand loo)in'

into your middle fin'er, the

forefin'er re&resents the a*is

!he (ase of your fin'ers is the

start &oint or 0.1, 1, +12


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Axis and motion nomenclature Rotarymotion designation

!he ri'ht-hand rule for determinin' the correct a*is on aCNC machine may also (e used to determine the

cloc)wise rotary motion a(out ., , and +

!o determine the &ositi%e, or cloc)wise, directiona(out an a*is, close your hand with the thum( &ointin'

out

!he thum( may re&resent the ., , or + direction and the

curl of the fingers may represent the clockwise, orpositive, rotation about each axis.

!hese are )nown as A, B, and C and represent the rotary

motions about X, Y, and , respectively.


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A*is and motion nomenclature CNC mill

n this 'antry mill the s&indle tra%els alon' the X Axis !he

tra%el direction of the ta(le desi'nates the Y Axis !he Axisis

desi'nated (y the stationary %ertical column


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is and motion nomenclature CNC lath

n most CNC lathes the Axisis &arallel to

the s&indle and lon'er than the X Axis


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A*is and motion nomenclature -a*is CNC

contour mill

n this fi%e-a*is hori5ontal contour millin' machine, note the

orientation of the X and Y a*es in relation to the Axis !he

rotary a*es for (oth theX and Ya*es are desi'nated (y the Aand

Brotary ta(les


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A*is and motion nomenclature %ertical CNC

)nee mill

n a common %ertical )nee CNC mill the s&indle isstationary while the rest of the com&onents mo%e

accordin' to their a*is desi'nations 0X, Y, and 2


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A*is and motion nomenclature CNC &unch

machine

n a CNC &unch &ress the &art is mo%ed in the X

and Ydirections while the &unch is stationary


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CNC millin' fundamentals !he three

Cartesian &lanes

!he three &lanes in the Cartesian coordinate system are XY,

X, and Y. !hese are referred to as !"#, !"$, and !"%,

res&ecti%ely, on the mill


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CNC millin' fundamentals !he &art reference

5ero


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!he %ideo illustrates the two reference &oints on a

CNC Machine6Machine Reference Zero0M7+2and

thePart Reference Zero0P7+2All coordinates are(ased on these two &oints

All CNC machine tools re8uire a reference &oint

from which to (ase coordinates &t is generally easier to use a point on the

workpiece itself for reference, because the

coordinates apply to the part anyway ' thus the

() designation. !he P7+is defined as the lower left-hand corner

and the to& of the stoc)of each &art


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!he ad%anta'es of ha%in' the P7+ at the lower left to&

corner are6:eometry creation is in the &ositi%e . &lane for

CAD/CAM systems

"!he corner of the wor)&iece is easy to find

3All ne'ati%e + de&ths are (elow the surface of the

wor)&iece


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!he Cartesian 'ra&h

Cartesian coordinates werein%ented (y 7en; Descartes,

who is famous for the &hrase


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CNC millin' fundamentals A(solute coordinates

A(solute coordinates use the

ori'in as the reference &oint

!his means that any &ointon

the Cartesian 'ra&h can (e

&lotted accurately (ymeasurin' the distance from

the ori'in to the &oint,first in

the . direction, then in the

direction, and then, ifa&&lica(le, in the + direction


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Incremental coordinates use

the &resent &osition as the

reference &oint for the ne*t

mo%ement !his means thatany &oint in the Cartesian

'ra&h can (e &lotted

accurately (y measurin' the

distance (etween &oints,

'enerally startin' at the

ori'in

CNC millin' fundamentals Incremental

coordinates


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*X*)C&+* " A(solute Coordinates

=ill in the . and (lan)s with the a&&ro&riate a(solute coordinates

for &oints A throu'h >

A X-----, Y----- BX-----, Y-----

CX-----, Y----- X-----, Y-----

* X-----, Y----- / X-----, Y-----

! X-----, Y----- 0 X-----, Y-----


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*X*)C&+* 1Incremental Coordinates

=ill in the . and (lan)s with the a&&ro&riate incremental

coordinates for &oints A throu'h >

A X-----, Y----- B X-----, Y-----C X-----, Y----- X-----, Y-----

* X-----, Y----- / X-----, Y-----

! X-----, Y----- 0 X-----, Y-----


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CNC lathes share the same two-a*is coordinate system

!his allows for the transfer of CNC &ro'rams amon'

different machines, as all measurements are deri%ed

from the same reference &oints

In CNC turnin' there is a &rimary, or hori5ontal, a*is

and a secondary, or %ertical, a*is ?ecause the ma@or a*isalways runs throu'h the s&indle0hori5ontally2, the + a*is

is usually the lon'er one !he . a*is is &er&endicular to

the + a*is 0or %ertical2

It is im&ortant to remem(er that on most CNC lathes thetool &ost is on the to&, or (ac)side, of the machine,

unli)e on a con%entional lathe !his is why the tool is

shown a(o%e the &art in the simulation e*am&les

CNC turnin' fundamentals


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CNC turnin' fundamentals Cartesian 'ra&h for turnin'

hen measurin' . and + coordinates, use a central reference&oint Btart all measurements at this reference &oint, the ori'in

&oint 0.1, +12 =or all our e*am&les the origin is located at the

center right2hand endpoint of the workpiece ee& in mind that

at times the center left-hand end&oint of the wor)&iece may (e

used


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Diameter 0or diametrical2

&ro'rammin' relates the

. a*is to the diameter of

the wor)&iece =ore*am&le, if the wor)&iece

has a -in outside

diameter and you want to

command an a(solute

mo%e to the outside, youwould &ro'ram .1

C3C turning fundamentals Diameter &ro'rammin'


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CNC turnin' fundamentals 7adial &ro'rammin'

7adius 0or radial2

&ro'rammin' relates the

. a*is to the radius of the

wor)&iece =or e*am&le,for the same -in outside

diameter wor)&iece, you

would &ro'ram ." to

mo%e the tool to theoutside


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C3C turning fundamentals Absolute coordinates

hen &lottin' &oints usin'

a(solute coordinates, alwaysstart at the ori'in

0.1, +12 !hen tra%el alon'

the + a*is until you reach a

&oint directly (elow the

&oint that you are tryin' to

&lot rite down the + %alue

and then 'o u& until you

reach your &oint rite

down the . %alue ou nowha%e the .+ 0or +.2

coordinate for that &oint


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C3C turning fundamentals &ncremental

coordinates!he second method for

findin' &oints in a

Cartesian coordinate

system is (y usin'

incremental coordinates

Incremental, or relati%e,

coordinates use eachsuccessi%e &oint to

measure the ne*t

coordinate Instead of

constantly referrin' (ac)to the ori'in, the

incremental method

refers to the &re%ious

&oint


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*X*)C&+* " 4sing &ncremental Coordinates.

/ind the diametrical X and coordinates for points

A through *.A X-----, ----- BX-----, -----

C X-----, ----- X-----, -----

* X-----, -----


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*X*)C&+* 1sin' A(solute Coordinates

=ind the . and + coordinates for &oints A throu'h E

A X-----, ----- B X-----, -----

C X-----, ----- X-----, -----

*X-----, -----


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Date post:	26-Feb-2018
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