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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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Recommended