### Introduction to CNC Machining

```Coordinates, Axes, and Motion

We’ll first learn about axis systems.

Then we’ll investigate how the machines
understand where to move,

and the kinds of moves they can make
getting there.
Machining and CNC Technology by McGraw-Hill Higher Education
Unless it’s a multiplexed machine with several
 There
are 14
standard
axes
auxiliary
rotary
and linear
axes,defined
these nineby
arethe
adequate to
define mostAssociation
of the equipment
in used
Electronics
Industries
(EIA)
industry today.




for motion and position.
However,
for tomorrow’s
manufacturing
In this
course
we’ll study
9 of them.world,
that’s another question? Machines continue to
3 Primary
Axes X, Yare
and
Zto handle
evolve asLinear
central processors
able
more andRotary
more calculations
perand
nanosecond,
thus
3 Primary
Axes A, B
C
more functions
simultaneously.
3 Secondary
Linear
Axes U,V and W
Machining and CNC Technology by McGraw-Hill Higher Education


Whenever you are assigned to a new CNC
machine, the axis set must be identified as
the first order of business.
Here are the sets for three common
machines.
Machining and CNC Technology by McGraw-Hill Higher Education



It’s easy to identify the spindle, which is the Z
axis or it faces Z.
Then apply the Right Hand Rule by pointing
your right middle finger in the positive Z
direction.
Your fingers and thumb then form the
orthogonal axis frame (mutually at 90º)
Machining and CNC Technology by McGraw-Hill Higher Education
First identify the Z axis.
It’s parallel to the
spindle axis, and brings
the work toward and
away from the spindle.
 Pointing your middle
finger in the positive Z
direction, your index
finger and thumb form
the other positive axes.

Machining and CNC Technology by McGraw-Hill Higher Education
The set (my
fingers)
 Allremain
CNCinmachines use the X-Z or X-Y-Z frame,
the same
with each axis perpendicular to the others.
orientation to each
 That
relationship stays the same no matter how
other
no matter
their the
worldaxis set is rotated to suit the machine.
orientation

Toward stronger or more efficient machines
manufacturers arrange the set any way
convenient, but not the inter-relationship
between axes.
Machining and CNC Technology by McGraw-Hill Higher Education



The X axis on many turning
centers, is not
X Slanted
parallel to the floor, it slants forward.
That provides easy access to the turret for
setup work, Z
since the machine isn’t as wide as
level X axis machines. 90º
Plus chips and coolants slide right off to the
Thisbasin
lathe’s world
axis orientation is not level but it’s still an
catch
below.
orthogonal set.
Machining and CNC Technology by McGraw-Hill Higher Education


Whenever a machine features a rotary axis,
we identify it this way:
If it rotates around a line parallel to
X it’s an A axis
Y it’s B
Z it’s C
Machining and CNC Technology by McGraw-Hill Higher Education



Rotary axes can move a cutter head in an arc
Or they can move the workpiece in an arc.
In this film we see A and B auxiliary axes
moving simultaneously with X, Y and Z, to cut
this complex turbine blade.
Machining and CNC Technology by McGraw-Hill Higher Education


X+
Z+
To determine the direction of rotary motion,
Y+
Point the thumb of your
either
plus or minus A,B or C, we use the Rule
right hand in the direction
the rotary axis’ line of
ofofrotation,
Thumb.
X, Y or Z positive
direction.
It’s
based on the line about which the rotary
axis pivots, X, Y or Z
Positive
CAB
direction
Positive
Positive
direction
What motion?
Machining and CNC Technology by McGraw-Hill Higher Education




tip ofwork,
the drill isthe
at origin, X0, Y0, Z0, is known
In The
CNC
Y1.00, Z-1.00 Reference Zero (PRZ)
asX2.500,
the Program
to the PRZ which is
It’sRelative
the
starting
point for coordinates
the lower left corner on this
part coordinates in the program refer their
Most
distance from the PRZ.
For example.
Machining and CNC Technology by McGraw-Hill Higher Education



Occasionally we encounter the need for a
different kind of coordinate.
They do not refer to the PRZ but rather, to
their last position.
Incremental coordinates are jumps from
where you are to where you wish to go
next.
Machining and CNC Technology by McGraw-Hill Higher Education
CNC machines move their axes in five ways:
Rapid Travel
Linear single or multi axis straight line motion
Circular motion within a single plane.
Circular/Linear, also called 2 ½ dim. motion. Two axes
move in an arc while the third moves in a straight
line.
3-D motion few controls have the ability to move in an arc

using 3 axes simultaneously. Most approximate these arcs
through the power of the cam software.
Machining and CNC Technology by McGraw-Hill Higher Education
Trade Tip
Caution!
Depending
on the
Rapid
– as fast
as
power of the CPU, your
the machine
can
machine
will rapid in one
of
twomove
ways. Older
butcontrollers
with
take an unexpected nonlinear
the
ability
to with
path!
Newer
controllers
16-bit
or higher
reduce
speed
microprocessors follow the
operator
truethrough
linear motion.
over-ride
control.
Machining and CNC Technology by McGraw-Hill Higher Education
The next four motions all move one or more axes at
the rate specified in the program.
 The differences lies in how many axes are involved,
in a straight line, or arc.
 As motions become more complex, the CPU must
handle far more calculations per second by
interpolating each axes drive commands.

Machining and CNC Technology by McGraw-Hill Higher Education



To move axes simultaneously, to produce a
constant velocity along the line A-B, say at
400 inches per minute.
neither the X or Y axis will be moving at 400
IPM.
They will run at lower speeds that combine to
create the tool motion of 400 IPM.
Machining and CNC Technology by McGraw-Hill Higher Education
B
Programmed Rate 400 Inches
Per Minute
137.81 IPM Y Axis
A
375.87 IPM, X Axis Motion
Machining and CNC Technology by McGraw-Hill Higher Education


The linear interpolation required the control
to set each axis moving at constant values
but different rates.
The operator can over-ride the resultant tool
motion from 0% (no movement) up to 100%
or 150% on some machines.
Machining and CNC Technology by McGraw-Hill Higher Education


For arc motion at feed rate, the controller is
also interpolating as with linear.
The difference is it is constantly changing the
ratio between the axes involved, as the
curvature changes slants.
Machining and CNC Technology by McGraw-Hill Higher Education
Trade
Tip
Sometimes engineering
information
comes not in
polar coordinates,
often saves a but rather as
the formUsing
of
rectangular
dimensions,
trigonometry step during drawing or hand
the radius
and angle
program
writing! from a starting point.
 Those points
are more
easily
If the needed
significant
point defined
is defined inusing
radius- polar
angle, rather than X-Y, why do an unnecessary
coordinates
– a bolt circle for example.
calculation? Define it with an R-A coordinate on
your geometryaren’t
drawing.used inside CAM
 Polar Coordinates
generated programs, but they are very useful for
drawing the part geometry or when doing hand
program writing of polar entities.

Machining and CNC Technology by McGraw-Hill Higher Education

Mastercam X2 Beginner Training Tutorials
 Review Exercise 1, in Tutorial 2
 Review Exercise 2, in Tutorial 3

Email Subject Line
 LastnameMill2&3
 Only attach Zip2Go files for each part
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