J4123 CNC TURNING NOTE

POLYTECHNIC OF SULTAN SALAHUDDIN ABDUL AZIZ SHAH

CNC TURNING

By




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Mohd Sharizan Mohd Sharif


CONTENTS

CHAPTER 1
Introduction about CNC Turning machines
History about CNC Turning machines
Advantage and disadvantage
CNC Turning machines components
Types of CNC Turning machines components
CNC Turning Cartesian coordinate system
Cutting tools
Types of cutting tools

CHAPTER 2
Preventive maintenance and servicing of CNC Turning machines tools
Replacement parts inventory
The level of maintenance operations
Maintenance and repair
Preventive maintenance programs
A typical preventive maintenance programs
Machine command codes
Letter address commands

CHAPTER 3
Project example
Work step to enter the programmed code

CHAPTER 4
Safety rules for CNC Turning machines

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CHAPTER 1

INTRODUCTION OF CNC TURNING MACHINES

A conventional engine lathe or turret lathe is a common machine in just about
every machine shop. A lathe is used for machining cylindrical or conical work such as
shafts, rings, wheels, hores, threads and everything. The most common lathe operation is
removal or material from a round stock, using a turning tool for enternal cutting. A lathe
can also be used for internal operations such as boring, as well as for grooving, threading
and everything if a proper cutting tool is used.

Turret lathes are usually weaker in machining power than engine lathes, but they
do have a special carousel that holds several mounted cutting tool. An engine lathe has
often only one or two cutting tools mounted at a time, but has more machining power.
Typical lathe work controlled by CNC systems uses machines known in industry as the
CNC Turning Centres or common the CNC lathes.

The term „turning center‟ is a rather unpopular, but an accurate overall description
of a computerized lathe (a CNC lathe) that can be used for a great number of machining
operations during a single setup. For example, in addition to the standard lathe operations
such as turning and boring, a CNC lathe can be used for drilling, grooving, threading,
knurling and even burnishing.

It can also be used in different modes, such as chuck work, collet work, barfeeder,
or between centers. Much other combination also exists, CNC lathes are designed to hold
several tools in special turret, and they can have a milling attachment, indexable chuck, a
sub spindle, a tailstock, a steadyrest and many other features not always associated with a
conventional lathe design. Lathe with more than four axes also common. With constant
advances in machine tool techonologies, more CNC lathes appear on the market that are

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designed to do a number of operations in a single setup, many of them traditionally
reserved for a mill or a machining center.

HISTORIAL OF CNC TURNING MACHINES

Old manual engine turning and knee mills had no computer. The operator cut
good part by cranking on big shiny hand wheels, expertly coaxing the tool down the
desired path. After years of this back and dialing, the crank handles became hand
polished to a mirror finish.

The idea of using electric motor to do all this cranking came up during the trouble-
free 1950s. The big question was whether a motor could crank as accurately as a human.
An interesting solution written back in the ‟50s was recently post in the hallways of a
famous engineering university. Using the dual premise of electronic control and motion
feedback, a written proposal to the cranking dilemma had long existed in academia (and
the military establishment). Apparently, this design didn‟t move into widespread
commercial manufacturing.

Most of early motorized machine tool was temperamental, expensive and hard to
set up and operate. Early on, the market potential for dependable CNC machine tools was
solid. During the middle and late 1970s some exceptional computer numerically
controlled machine tools were introduced to the world market.

The factory standard use in the design and manufacture of these early CNC
machiones routinely provided years of flawless operation. A single machine in the late
„70s gave the profitability to the purchase one new machine after another. Shops with a
few of these mighty machines have done well to the present day.

The basic design of the system which was mass marketed in the „70s bore a
resemblance to the posted design from the „50s. Accurate control of electric motors was

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accomplished by closing the motion loop using early micro-processors and digital circuits
to track the command pulses going out and the motion feedback pulses coming back.
First generation machoines naturally use older technology than what is sold today.
Back then, the motor current for axis and spindle motion was provided by thyrister-
controlled, DC (Direct Current) motor drivers. Internal computer logic and control
function came from an 8-bit CPU (Central Processing Unit) built on a platform of
intricate, pressed wire-trace circuit boards and all were plugged into a collector‟s item
wire wound back plane. Memory data originally resided in old magnetic-donut memory
boards, which as since been replaced by compatible, modern IC RAM (Integrated Circuit
Random Acces Memory) memories.

The old 8-bit computers sense machine movement by counting signals from the
precision feedback unit mounted to each motor shaft. These units send motor direction,
speed and position information. Although costly, the complete feedback units were
designed to be replaced or exchanged.

Early, CNC Turning centers could move at 300 IPM (Inch Per Minute) and hold
two-tenths of an inch. The smallest position unit the computer displays is 1 um (One
Micron, Metric) or 1 tenth (One Ten-Thousandths, Inch). An active change of the
machine position flashes over a cluster of universal seven segment displays. In concert,
the displays form a some what coherent read-out for the operator to use in programming
and monitoring the machine.

Machines from the seventies are still running in production today, some 20 years
late! The best explanation for this longevity is a combination of stout, oversize
mechanicals and top-quality wiring and electronics running at the typically slower speeds.

The new machines of today are fast. Performance AC motors are driven at high
speed by compact vector-controlled digital inverter. But more astounding are the

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computer improvement: the new high speed RISC (Reduced Instruction Set Computing)
processors and the running of expanded software options from the open PC platforms.
Machine functions previously handled mechanically are now economical
accomplished using nifty NC software models. Industrial grade PC computers are now
upgraded with plug-in NC modules. Similar to the process of adding a modem or
installing a new software program, an entire numerical control is plugged in and
configured for machine. The closed CNC systems of the past are now beginning to open
up. The twenty-year transition from the first generation machines to the systems of today
frequently visited the concept of Kiazen, the study and implementation of continuous
process improvements.

ADVANTAGES AND DISADVANTAGES OF CNC TURNING MACHINES

CNC Turning machines have been continually improved to increase their
accuracy, efficiency, and productivity. Most modem CNC Turning machines are accurate
to within 0.0002 inch positioning and repeatability. They are also capable of positioning
the cutter (toolholder) at a rate 700 inches per minute or greater.

Additionally, CNC Turning machines can be designed with various options. For
example, CNC Turning machines can be equipped with tool sensing sytems, with two or
more spindles, additional turrets and „live tooling‟. The tool sensing sytems is designed to
quickly and accurately find and store each tool tip offset value.

The dual spindle option allows turning of two parts at the same time. By adding
another tool turret it provides greater workpiece machining flexibility and reduces setup
requirements. The live tooling option allows secondary machining such as milling and
drilling operations to be performed in the same turning operation.
The Following Is A List Of Advantages That Can Be Derived From CNC
Turning Machines

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 CNC Turning machines can be used continuously 24 hours a day, 365 days
a year and only need to be switched off for occasional maintenance.
 CNC Turning machines are programmed with a design which can then be
manufactured hundreds or even thousands of times. Each manufactured
product will be exactly the same.
 Less skilled or trained people can operate CNC‟s unlike manual turning or
milling machines which need skilled engineers.
 CNC Turning machines can be updated by improving the software used to
drive the machines
 Training in the use of CNC‟s is available through the use of „virtual
software‟. This is software that allows the operator to practice using the
CNC Turning machines on the screen of a computer. The software is
similar to a computer game.
 CNC Turning machines can be programmed by advanced design software
such as Pro/DESKTOP®, enabling the manufacture of products that cannot
be made by manual machines, even those used by skilled designers or
engineers.
 Modern design software allows the designer to simulate the manufacture of
his/her idea. There is no need to make a prototype or a model. This saves
time and money.
 One person can supervise many CNC Turning machines as once they are
programmed they can usually be left to work by themselves. Sometimes
only the cutting tools need replacing occasionally.
 A skilled engineer can make the same component many times. However, if
each component is carefully studied, each one will vary slightly. A CNC
Turning machines will manufacture each component as an exact match.
 Simple to complex operations can be executed on a single CNC Turning
machines.
 Greater accuracy and piece-to-piece consistency.

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 Finer dimensional tolerances are achieved within tight statistical process
control parameters.
 Automatic part loading devices can accommodate a variety of work pieces
with only minimal adjustments for consistent production rates.
 CNC Turning machines reduce setup time
 CNC Turning machines reduce handling, which improves quality and
production.
 CNC Turning machines run automatically without operator intervention.
 CNC Turning machines output maximum part accuracy.

The Following Is a List of Disadvantages That Can Be Derived From CNC
Turning Machines

 CNC Turning machines are more expensive than manually operated
machines, although costs are slowly coming down.
 The CNC Turning machine operator only needs basic training and skills,
enough to supervise several machines. In years gone by, engineers needed
years of training to operate centre lathes, milling machines and other
manually operated machines. This means many of the old skills are been
lost.
 Less workers are required to operate CNC Turning machines compared to
manually operated machines. Investment in CNC Turning machines can
lead to unemployment.
 Many countries no longer teach pupils or students how to use manually
operated turning or milling machines. Pupils or students no longer develop
the detailed skills required by engineers of the past. These include
mathematical and engineering skills.
 Tools on CNC Turning machines do not cut metal any faster than
conventional machines.

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 CNC turning machines does not eliminate the need for expensive tools.
There is also a greater initial cost involved with the CNC Turning
machines.
 CNC Turning machines will not totally eliminate errors. Operators can
still fail to push the correct buttons, make incorrect alignments, and fail to
locate parts properly in a fixture.
 Selection and training of programmers and maintenance personnel is
required.

CNC TURNING MACHINES COMPONENTS

CNC Turning machines and convertional turning machines each have the same
basic components, such as the main motor, the spindle, the bed, the tool turret, the
headstock, the cross-slide, the carriage and the way systems. However, CNC Turning
machines, in addition, are outfitted with a computerized control and servomotors to
operate them.

Manual CNC Turning can be very versatile and productive machine tools, but
when coupled with a CNC, they become the „high tech production turning machines‟ of
the machine shop. Additionally, repetitive operations such as turning, facing and boring
are ideal machining applications for CNC Turning machines.

CNC Turning machines can also be designed to include a variety of optional
components and features. These options are basically designed to reduce setup time, part
handling and cycle time. For instance, one option for minimizing part handling time is to
add a part loading magazine or a robot arm. The maximum spindle speed (RPM) of a
CNC Turning machines can also very depending on the need or application.

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The factors that determine the spindle speed range selected can include the type of
part materials, the part sizes and the annual part production quantities to be machined.
Another factor that influences the spindle speed range is the type of tool cutter material
that will be used, such as HSS, coated carbide, diamond and ceramic.

High-production turning machines can be designed with dual chucks that enable a
part to be machined on both ends. Also, live tooling can be incorporated that allows
milling and drilling at various angles. Other options may include a second or third turret,
a bar feeder, a parts catcher, a steady rest follower and a tool setter.

Picture: CNC Turning machines.

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Types Of Components CNC Turning Machines:

The main components of the CNC Turning machines include the bed, the
headstock, the cross-slide, the carriage, the turret, the tailstocks, the ways, the servomotor,
the ball screws, the hydraulic and lubrication systems and the machine control unit
(MCU).

The two primary axes of a CNC Turning center are the X-axis and the Z-axis. The
X-axis, which controls the cross-slide, moves the cutting tool to control the workpiece
diameter. The Z-axis, which controls the carriage, moves the cutting tool lengthwise, to
control the workpiece length.

Picture: CNC Turning machines components.

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i. CNC Turning Control :

The modern CNC Turning machine tool is software driven. The computer controls
are programmed instead of hardwired. The control panel is where the machine operation
buttons and knobs are located. The control panel typically includes the following items :
 Power On/Off button.
 Cycle Start button.
 Axis Select knob.
 Spindle Override knob.
 Load meters.
 Keyboard pad.
 3.5-inch input disk drive.
 Feed Hold button.
 Emergency Stop button.
 Axis Jog wheel.
 Feed Override knob.
 Turret Index button.
 Mode select Knob.
 Miscellaneous function button.

ii. CRT Display :

The CRT is also located on the control panel. The CRT display allows the
operator easy visual access to CNC program and machine information. On the screen of
the CNC control, the operator can view the CNC program, active codes, tool and
workpiece offsets, machine positions, alarms, error message, spindle RPM and
horsepower.

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iii. Bed :

The bed is designed to support and align the X-Z axes and cutting tool
components of the machine. Bed is designed in two ways: they either lie flat or at a slant.
Most lathes have a slant-bed design, providing the operator easy access for loading
and unloading parts and tools. It also allows the chips and coolant to fall away from the
cutting area to the bottom of the chip conveyor.

iv. Headstock :

The headstock contains the spindle and transmission gearing or belts, which
rotate the chuck and workpiece. A variable speed motor drives the headstock spindle,
which is programmed in RPM. They are typically equipped with a variety of motor sizes
ranging from 5 to 75 horsepower and spindle speeds from 32 to 5500 RPM.

v. Chuck and Jaws :

The chuck is mounted to the spindle and is equipped with a set of jaws to grip
and rotate the workpiece. They are categiorized into two groups: manually operated or
automatically power operated. The chuck can be designed as a 2-jaws, 3-jaws, 4-jaws, 6-
jaws or a collect jaw type.

The jaws are either hardened (hard jaws) or mild steel (soft jaws) and are selected
depending on the operation holding requirements. The hard jaws are available in various
standard design. The soft jaws are also available in various standard design, but they
require a boring operation to match the diameter that they will hold. Collect jaws are
designed to grip barstock, which can be round, square and hexagon.

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Picture: The 3-Jaw chuck features.

vi. Tool Turret :

Tool turrets come in all styles and sizes. The basic function of the turret is to
hold and quickly index the cutting tools. The CNC Turning usually is equipped with one
turret that can hold from four to twelve tools.

The type and number of turrets on a CNC Turning can vary with the size of the
machine and the manufacture. Most turrets are capable of bidirectional indexing and the
slides on which the turrets are positioned can travel at a rapid rate of approximately 400
in./min, which reduces noncutting time of the machine cycle.

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Picture: Turret description.

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vii. Tool Indexing :

This design allows a lathe tool to be fastened in each turret station so it can be
indexed automatically during the CNC program cycle. Quick tool indexing is an
important factor on CNC Turning machines used for production purposes. Therefore, the
index time is typically completed within seconds.

viii. Tailstock :

The tailstock is used to support workpieces that lack rigidity such as long shafts,
long hollow castings and similar parts. The tailstock can be designed to operate either
manually or by CNC program commands. The tailstock basically supports one end of the
workpiece with a center. The most common is the live center, which rotates on a bearing
pack to eliminate friction. The tailstock travels on its own hardened and ground-bearing
ways.

Picture: Tailstock and center.

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Picture: Tailstock center.

Picture: Tailstock setup.

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ix. Ways and Way Covers :

The ways are precision-hardened rails that allow the turret to travel in rapid
traverse and feed motion (X and Z axes). The way covers are a means of protecting the
ways from damage due to scraping from metal chips or due to dents from metal items
such as tools or parts.

x. Way Lube System :

The way lube system is designed to keep the ways lubricated, which will reduce
wear from friction and eliminate early machine failure. The operator and maintenance
personnel must check the way lube system reservoir level on a daily basis.

xi. Electrical Control Panel :

The electrical control panel is where the main Power On/Off switch is usually
located. This also where all the electric components, including fuses and reset buttons, are
enclosed for safety. The electrical control panel is usually locked to prevent entry by
unauthorized personnel. An authorized electrician should be contacted if entry is
required.

xii. Ball Screw :

The ball lead screw uses rolling motion rather than the sliding motion of a
normal lead screw. Sliding motion is used on conventional acme lead screws. Unlike the
ball screw, the motion principle of an acme lead screw is based on friction and backlash.
Below are some advantages of the ball screw versus the acme lead screw :
 Less wear.
 Longer life.
 High speed capability.

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 Precise position and repeatability.

xiii. CNC Turning Tailstock Setup Description :

The illustration typically setup for a workpiece, which requires a tailstock. The
workpiece, which must be center drilled at one end before the CNC Turning machines
operation, is held at one end with the 3-jaw chuck and supported at the other end with the
tailstock. The tailstock and center are required to support it during machining operations
when the turn tool is cutting the workpiece.

xiv. Servo Drive Motors :

CNC machines use electric servomotors that turn ball screws, which in turn drive
the different axes of the machine tool. The axes (X and Z) each have a separate
servomotor and ball screw to control each axis independent of each other.

xv. Auto Bar Feeder :

This option can be added to reduce the handling time required for loading the
workpiece material into the chuck. The bar feeder can be designed as a single tube type or
magazine type. The purposes of the bar feeder is to quickly load more stock automatically
at the end of the CNC machine cycle.

xvi. Parts Catcher :

The purposes of the parts catcher is to catch the part immediately after it is cut
off and avoid damage to the part, tools and machine components. This option is typically
included with bar-feed-type machines.

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xvii. Secondary Turret :

The main turret and the secondary turret are designed to work independently of
each other. This design of the turrets allows simultaneous cutting with two tools to reduce
the cycle time. The main turret is a two-axis design.

xviii. Subturret :

This design of the turrets also allows simultaneous cutting with two tools to
reduce the cycle time. The subturret is typically a single-axis design, which uses the B-
axis travel.

xix. Tool Setter :

The tool setter is a sensing device on the machine that automatically refrences
each tool in a setup. The control then automatically records the distance values in the
offset storage memory. This optional device can minimize setup downtime and improves
the quality of the parts produced.

xx. Dual Spindle/Chuck :

The dual spindle and chuck design allows the CNC machine to automatically
machine the first operation, then transfer the workpiece to the second chuck and machine
it simultaneously. This produce is designed to complete all the turning operations and
thus minimize lead time.

xxi. Chip Conveyor :

The chip conveyor is designed to remove the metal chips produced from the

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workpiece machining operations from the CNC Turning work area. When operating, the
chip conveyor typically transfer and deposits the metal chips into a dumpster. This also
controls the handling of metal chips for recycling.

xxii. Open-Loop Systems :

The stepping motor is an electric motor that rotates a calculated amount every
time the motor receives an electronic pulse from the MCU. The stepping motor‟s rotary
motion is converted into the linear motion of the machine axes through the use of lead
screws. The open-loop system is simpler and rarely used for CNC machines that require
accuracy and repeatability.

xxiii. Closed-Loop Systems :

Servomotors permit automatic operation of the machine and the closed-loop
control system verifies that the machine accurately positions the CNC program
commands. The computer makes it possible to continuously monitor the machine‟s
position and velocity while it operating.The advantages of the servomotor are increased
accuracy and repeatability.

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Picture: CNC Turning closed-loop system diagram.

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CNC TURNING CARTESIAN COORDINATE SYSTEM

The Cartesian coordinate system is applied to CNC machine tools in various ways.
The most common application for CNC lathes is the X-axis and the Z-axis. On a CNC
turning machine, the X-axis specifies the diameter coordinate movement, and the Z-axis
specifies the length coordinate movement. A coordinate position command always start
with a letter “X and/or Z” code followed by a numeric value that represents the travel to
coordinate point.

Picture: Cartesian coordinate system for CNC Turning machines.

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Picture: Cartesian coordinate systems for CNC Turning machines.

CUTTING TOOLS

The CNC operator must be thoroughly knowledgeable in machining operations
that pertain to the type of CNC machine to be operated. The CNC tooling is directly
linked to the machining operations planning process. There is various type of holders and
tools types used in CNC machining operations. The most commonly used OD cutting
tools on CNC are carbides, twist drills, boring bars, reamers and taps.

Types of Cutting Tools

a. Carbides indexable insert drills :

Represent the latest state of the art advancements in CNC hole drilling. It can drill
holes at much hinger metal removal rates than HSS twist drills. The advantage of

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indexable or replaceable inserts that can save time during setup and tool changes. The
carbides inserts also allow the tool to be driven into harder materials.

Picture: Features and description of carbide drills, spade drills and holder.

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b. Twist Drills :

The twist drill is used to produced a hole in the center of the workpiece. The twist
drill is made from various types of materials, which includes HSS, cobalt, solid carbide
and carbide tipped.

c. Boring bars :

Boring bars are used in situations where high accuracy or fine surface finish of hole is
required. Boring bars typically produce better hole straightness and roundness.

Picture: Features and description of boring, grooving and threading bars.

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d. Reamers :

Used in situations where high accuracy and fine surface finish of a hole is required.
The factor that basically determines use of a reamer or a boring is the diameter size. A
reamers is usually selected when the hole size is 0.125inch up to 0.625inch in diameter.

Picture: Features, description and types of reamers.

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e. Taps :

There are various thread forms, which are machined on lathes. Some common thread
forms include the „Acme‟ thread, the „buttress‟ thread, the „square‟ thread and the
„unified‟ thread.

Picture: Features, types and identification of taps.

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CHAPTER 2

PREVENTIVE MAINTENANCE AND SERVICING OF CNC TURNING
MACHINES TOOLS

Replacement Parts Inventory

Most CNC manufactures have list recommending the most frequently needed
replacement parts. Parts less frequently needed are normally available from the
manufacture within 24 hours. Potential CNC users are already purchasing complete
reserve control from which parts can simply be taken as needed. This process simplifies
and accelerate repair from many point of view:
 Any required part is always available.
 The hardware cost for the complete control are less and then for the
replacement parts.
 Downtime is kept to a minimum
 In the event of the significant malfunctions, damage or total brake down of the
control the complete controller can be exchanged
 The standby control is available for the testing purposes and for comparative
research
 The control can be used to train operating and maintenance personnel.

The Level of Maintenance Operations

a. Planned and preventive maintenance
b. Repair of breakdowns

The size of the firm usually has a great impact on its ability to maintain and
repair modern CNC equipment. Larger firms are more likely to have adequate number of
skilled, trained and experienced repair personnel than smaller firms. As smaller companies

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have to accept a lower level of repair capability, preventive maintenance is even more
important to them. Obviously the degree of repair capability by in house personnel is also
dependent on the number, complexity, and variety of machine installed. The experience of
larger CNC users in United States has shown that one technician is able to master
approximately four different hard wired CNC system but only two different CNC systems.

The first level of preventive maintenance and vital one is routine maintenance of
the machine. The includes checking oil levels and hydraulic and pneumatic pressures and
inspecting and charging oil filters.

There are many ways of drawing up a simple but effective controller preventive
maintenance program, and such routine inspections should lie within the capabilities of
most users. The required instruction and guideline for such programs are obtainable from
the equipment manufacturer or may be worked out by the users with help of the
manufacturer‟s personnel during the installation period. A checklist with the daily, weekly
monthly and yearly operations to be carried out should also be prepared along the lines of
the proposed.
c. Typical guidelines are:

 If the power supply for the electronics does not always delivered a
perfectly stable voltage, voltage fluctuations, noise or brief power failure
can occur. Excessive voltage can caused damage especially to ICs and
other electronic components. Low voltage and interference voltages are
often the cause of malfunctions which appear intermittently and hard to
locate. There four the power supply should be checked every three to six
month and compared with the manufacturer‟s specifications. Ripple
voltage or bad connections can then often be identified before they cause
major breakdowns.
 The so-called “clock oscillator” and other frequency generators which
control feed rate and system frequencies can drift with time. This can result

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in irregular machine movement or measurement deviations caused
sinusoidal changes in resolver or inductosyn measuring voltages.
Therefore, frequency regulation testing should also take place ever y six to
twelve months.
 Faulty feedback signals are often a cause of positioning errors. First the
tachometer voltage should be checked for uniformity and absolute value. I
the brush are uneven or if the slip ring is dirty, strong voltage interference
can result, and this noise is amplified even more by the control loop which,
in turn can cause rough machine feeding, hard stop or triggering of safety
device. It is therefore recommended that brushless tachometer be used on
the original installation or as replacement parts. Defective optical encoders
can also produce similar malfunction and their power supplies should be
checked every three to six months for proper voltage levels.
 The servo amplifier is balanced for drift, amplification and machine
dynamics at the time installation. This balancing procedure should be
repeated every three months in order to determine whether its ratio has
change in any of the axes. Drift can change data position and path
precision, leading to over shoots and damage the drive components.
 The quarterly function check of over travel limits switches and emergency
stop switch is vital. These switches should be checked for correct actuation
and proper secure mounting. Malfunction for such a limit switch can lead
to expensive machine damage but can avoided by performing the simple
preventive maintenance check.
 One of the most frequent causes of failure can be avoided by routinely
checking the data input devices on the CNC. This should include cleaning,
lubricating and adjusting any tape readers and spoolers. Indicator lamp
should be checked to ensure they light promptly to indicate danger or
function status to the operator.
 Documentation is another important area. All malfunctions and
maintenance operations should be accurately recorded in maintenance log

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located in every CNC. Recurring serious areas for malfunction can than be
quickly be noted. Such a log also provides a valuable maintenance history.

Maintenance and Repair

The CNC machine is an electromechanical installation which encompasses a wide
range of technologies, including mechanical components, hydraulics, pneumatics, electro
technology and electronics. As a result of the CNC machine demands a high standard of
knowledge and experience of the part of maintenance technicians.

Training programs for the technician maintenance technicians often to go too
much detail. A classic example will be study of the interpolator logic for linear/ circular-
interpolating continuous part control. The explanation of this principle which often take
one or two days, serves only to satisfy the technical curiosity of trainers and does nothing
to assist in elimination of CNC malfunctions.
Caution should be exercised with respect to randomly exchanging plug in
modules; this can be costly practice. Components may be damaged during the exchange
process, an inventory of parts will grow containing damaged components and more
damage will be done to the machine.

The systematic approach of error location is much better. In this context, CNC can
be divided into three main groups :

Group 1: Machine tool: axis and spindle drives, machine components,
hydraulics and pneumatics.
Group2: Measuring System and Control Loops including transfer systems
Group3: Electronic Control: technology for digital and data processing, logic
links, input and output units.

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Through intensive cross linking of these group- through control loops, measuring
circuits and interlocks.

Preventive Maintenance Programs

From evaluation of previous experience in preventive CNC maintenance, the
following guidelines are suggested:
 Leave well-functioning components alone! Do not alter any setting and do not
dismantle or rebuild any devices without good reasons.
 Each time the system is serviced, pay special attention to sign of possible
future malfunctions: corrosion, loose connections, discolored contacts and any
material will may be present whose origin is unknown.
 The three most important preventive maintenance function to be carried out on
a timely basis are cleaning, lubricating and inspecting as prescribed by the
manufacturer.
 Use only as much lubricant as needed.
 Diagnosis and electrical should only take place in accordance with appropriate
written instructions. Deviation noted should be corrected immediately if
possible.
 Preventive maintenance should reduce downtime to a minimum. Therefore
used available replacement parts as much as possible and repair defective parts
in your shop or send them back to the manufacture once the machine is back
in operation.

A typical preventive maintenance programs looks like the following

a. Weekly :
 Run a short program and alter the feed rate override control between
minimum and the maximum.
 Test deficiencies and complaint operator.

33


 Check all fans for the operation and pay attention to good air circulation.
 Check the appearance of functioning of any tape reader paying special
attention to wear of drives and reeler, cleanliness of read head and
alignment of channel and transport tracks.

b. Monthly :
 Test a part program without using a work piece and observe the axes for
the stability, uniform movement, positioning behavior and so on.
 Oils all fans, of applicable
 Make sure that all plug in circuit are correctly positioned in the contact
strips and the retainers are in the place.
 Check moving cable and plugs for worn or damages wires and connections.
 Remove yhe cover of each measuring system and check for dirt, cable
condition, and condition of connections.
 Reorder replacement parts for those which have been used.
 Check maintenance logs for problems by operating personnel-especially
repetitive problems.

c. Semiannually :
 Measure the mutual dependency of speed/tachometer voltage and
following error as the function of the command voltage. Compared the
measured value with value measured at the time of installation.

d. Annually :
 Test each circuit board for perfect seating in its contact strip.
 Inspect all contact strips for damage or breakage.
 Checked doors, seals and screw fitting for loose connections.
 Clean console with vacuum cleaner and soft brush as necessary
 Test tape reader mechanics for good working condition.
 Test functioning and precision of the CNC.

34


 Test power supply for correct voltage output.
 Complete fictional test of CNC by processing a test part program with and
without a work piece.

MACHINE COMMAND CODES

The CNC machine receives a series of commands via the CNC program. These
commands are structured using letters and numbers such as G00, S2300 and M03. Each
letter and number combination gives the control a specific command. There are some
codes differences between the various machine tool and control manufacturers. Therefore,
each machine and control manufacturer provides a specific manual listing all the
commands. Most CNC codes are identical, while some may vary slightly or entirely.

Letter Address Commands

Most letter address codes fall into two categories : modal and nonmodal .
 Nonmodal : command codes that are only active in the block in which they are
specified and executed.
 Modal codes : codes that once executed will remain active throughout the
program until another code n the same group overrides or cancel its.

a. The M codes :
Perform a miscellaneous machine function such as automatic tool changes, coolant
control and spindle operations.

b. The G codes :
Set preparatory machine functions such as rapid traverse mode, feed mode and
active tool length offsets. Spindle speeds are controlled with the S code followed by up to
four digits to specify the RPM.

35


Picture: World address codes and description.

36


Picture: Preparatory function G code description.

37


Picture: Miscellaneous function M code description.

38


CHAPTER 3

PROJECT EXAMPLE

Picture: Project example is bottle water.

39


Picture: Autocad design about bottle water.

40


WORK STEP TO ENTER THE PROGRAMMED CODE

 START PROGRAMMED :
%
0 5451
G59 : X0, Z208
G96 : V200, T0202, M03
G92 : S2000, M08

 FACING OBJECT :
G00 : X20, Z0
G01 : X-1, Z0, F0.2
G00 : X20, Z2
G71 : P60, Q70, I0.02, K0.02, D1, F0.2
G26

 SUB PROGRAMMED :
N60
G46
G00 : X0, Z0
G01 : X5, Z0
G01 : X5, Z-5
G01 : X18, Z-12
G01 : X18, Z-22
G01 : X16, Z-23
G01 : X16, Z-30
G01 : X18, Z-31
G01 : X18, Z-48
G40
N70

41


G26

 CUTTING
G96 : V200, T0101, M04
G92 : S2000, M08
G00 : X20, Z-49.5
G01 : X14,
G00 : X15,
G01 : X10,
G00 : X11,
G01 : X6,
G00 :X7,
G01 : X2,
G00 : X3,
G01 : X0,

 END PROGRAMMED :
G26
M05,M09
M00
%

42


CHAPTER 4

SAFETY RULES FOR CNC TURNING MACHINES

These safety rules are generally applicable to most CNC machine operating
situations. Most machine shop safety rules and safe guards for operating CNC Turning
are specified and enfoerced by OSHA and ANSI guidelines are applied to safety
equipment. Therefore, it is highly recommended that people has to follow the rules when
they get inside the worksyop.

Additionally, the doors are usually hardwired with switches, which will prevent
the CNC Turning spindle from operating whenever the doors are open. Another built-in
safety feature prevents the CNC Turning spindle from operating whenever the chuck jaws
are unclamped. An important safety feature that is built-in for CNC Turning and most
machines alike is the „way-lube-fault‟warning.

This safety feature will also prevent the spindle from operating whenever the
lubricant in the way lube reservoir diminishes to a low level. The following is a
categorized list of recommended safety rules that the reader is strongly advised to fully
read and understand before attempting to operate CNC Turning machines.

a. Personal safeguards :
 Keep long hair covered when operating or standing near lathe.
 Avoid skin contact with any cutting fluids or oil.
 Always report any injury and apply first aid treatment.
 When the spindle is rotating, avoid standing directly in front of the chuck.
 Wear safety shoes when working with heavy tools and equipment.
 When ANSI-approved safety glasses with side shields at all times in the
shop areas.
 Wear hearing protection for noise levels that exceed OSHA specifications.

43


 Wear an approved face mask for dust levels that exceed OSHA
specifications.
 Do not wear jewelry or loose clothing while operating or standing near
lathes.
 Do not operate any lathes or equipment while under the influence of drugs
(prescribed or otherwise)

b. Shop environment safeguards :
 Remove chips from the floor.
 Clean all liquid, oil, and grease spills immediately.
 Keep floors and walk aisles clean.
 Report any fumes or odors.

c. Lathe and tool handling safeguards :
 Always remove hand wrenches after tightening or untightening.
 Always remove chuck wrenches after tightening or untightening.
 Store tools in their appropriate tool trays and racks.
 Keep tools sharp and in good working condition.
 Keep tools, parts and any other items off the lathe and part.
 Keep all electrical and mechanical panels secured in place.
 Check that oil levels are maintained and sufficient.
 Check that all safety guards and devices are in place and working before
operating any lathe.
 Check that all compressed air equipment is in good working condition.
 Do not handle loose wires or electrical components.
 Do not used compressed air to clean chips.
 Never use gloves when operating a lathe or cleaning the chips.
 Use gloves when handling tools by their cutting edges.

44


d. Safe machining practices :

 Do not open the electrical panel or control doors when the machine is
operating.
 Maintain a continuous flow of coolant to the cutting tools when it is
operating.
 Do not remove the chips with a hand when the spindle is finishing its job.
 Keep hands clear of all moving machines components.
 Keep hands away from spindle while it is rotating.
 In case of any emergency while operating a machines, immediately press
the Emergency Stop button.
 Use caution to avoid inadvertently bumping any CNC control buttons.
 Check that all feeds and speeds do not exceed recommended values.
 Always consult with an authorized person if you are uncertain or
unfamiliar with any operation.

45

J4123 CNC TURNING NOTE

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