Machining

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Machining

• Q7

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Introduction.

• Topics Machines
• Drill
• Lathe
• Grinder
• Milling machine
• Shaping machine
• CNC machines.
• Robotics

3
Introduction.

• Associated Terms.
• Cutting fluids.
• Surface finish
• Forces
• Measurement's.
• Tool geometry.
• Work holding.
• Chip formation

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1. PARTS OF DRILL BIT

• A Body. This section of the drill contains the
  drill flutes.
• B Parallel shanks. This section of the drill bit
  is held by the chuck.
• C Flank This determines the cutting lip length
• D Flute. These provide the passageway for swarf
  to escape up the drill
• E. Land. This is the thickness of the cutting
  lip
• F Web this is the edge between both flanks

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Parts of Drill Cont.
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Reaming.

• Reamers are used to accurately finish holes
  drilled by drill bits.
• Reamers contain more flutes than a drill.
• Drill bit Reamer

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Terms.

• Countersinking is the enlarging of the mouth of
  a drilled hole to accommodate countersunk head
  screws and rivets.

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Pilot Hole

• A pilot hole is drilled prior to drilling a large
  hole.

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Counterboring

• It is the increasing of the hole diameter to a
  certain depth to accommodate cheese head screws

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The Centre Lathe.
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Lathe Processes.

• Parallel turning.
• Facing off.

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Lathe Processes Cont.

• Taper turning
• Parting off/Undercut

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Lathe Processes Cont

• Radius nose turning.
• Drilling.

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More Lathe Processes
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Cutting Tools.

• The tool used in a lathe is known as a single
  point cutting tool. It has one cutting edge or
  point whereas a drill has two cutting edges and a
  file has numerous points or teeth.

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Lathe Tool Shears Workpiece.

• The lathe tool shear the metal rather than cuts.
  It can only do so if there is relative motion
  between the tool and the work piece.
• For example the work is rotation and the tool is
  moved into its path such that it forms an
  obstruction and shearing takes place.

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Lathe Tool Shears Workpiece
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Screw Cutting.

• It is slightly more difficult task than plain
  turning.
• It involves more accurate setting up of the tool
  and exact setting of feed in relation to the work
  rotation.
• Once this is done however, the process is easy.

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Screw Cutting
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Bench Grinder.
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Grinder

• A bench grinder or pedestal grinder is a machine
  used to drive an abrasive wheel (or wheels).

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Grinding Wheels.

• The wheel can be fitted to the spindle of the
  grinding machine.
• The wheel rotates at high speed and the work is
  brought into contact with it.

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Parts of the Grinding Wheel.

• There are two main constituents in a grinding
  wheel
• 1 The abrasive (this is the grit)
• 2. The bond. (this holds the abrasive in a rigid
  shape.

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The Abrasive.

• The abrasive forms the cutting edges.
• Usually, a particular abrasive type is selected
  to suit the materials being ground.
• The surface finish required on the work
  influences the size of the abrasive grains
  chosen.

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The Bond

• The bond, while designed to hold the abrasive in
  the form of a wheel, also must release the grains
  when they become worn.
• There will be greater pressure on grain from the
  work if it has lost its cutting ability so it
  well become dislodged exposing sharper grains
  underneath.

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Dressing the Grinding Wheel.

• In the grinding process, wheel dressing is used
  to restore the cutting surface of any
  irregularities. Grinding wheels are designed to
  have a selfdressing action in which grains should
  break free and expose sharp edges.
• Wheel dressing will renew a sharp cutting face
  and correct irregularities such as wheel
  concentricity.
• The process can remove any undulations from the
  wheel.

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Loading Grinding Wheel

• Loading of a grinding wheel occurs when small
  particles of the metal being machined clog up the
  spaces between the abrasive grains in the
  grinding wheel

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Loaded Grinding Wheel.
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Glazed Grinding Wheel.

• Glazing occurs when abrasive particles which have
  lost their edge remain trapped in the grinding
  wheel.

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DIAMOND STICK WHEEL DRESSER
http//its.fvtc.edu/machshop1/Bench/grinder/video/
dresssideLG.mov
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The Wheel Grit

• Coarse Grit Fine Grit

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Surface Grinding

• A metal cutting process in which flat and
  extremely smooth surfaces are produced. The
  grinding wheel rotates and the workpiece, usually
  held in a magnetic chuck, is fed to and fro
  continuously.
• At the end of each stroke, the table is moved
  across the wheel by a small amount.
• The grinding wheel can be lowered to take a new
  cut

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Surface Grinding Cont
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Work holding for the Surface Grinding.

• The magnetic chuck is used to hold work on the
  surface grinder. It consists of a top plate,
  which contains magnetic inserts, a casing which
  contains permanent magnets.
• To turn the chuck on the magnets are moved on
  line with the inserts, which creates a magnetic
  force through the work piece.
• The force is strong enough to hold the work piece
  securely in position.

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Other Workholding methods for Surface Grinding.

• Adaptor plates, sine chuck, chuck plates,
  universal plates and magnetic chucks

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Cylindrical Grinding

• This is used to produce cylindrical objects. The
  workpiece is held in a chuck, or between centres,
  and set to rotate.
• Then a grinding wheel, when brought into contact
  with the workpiece, will produce a smooth
  accurate cylinder.
• Long workpieces can be ground as the table can
  reciprocate and the wheel head can move towards
  the workpiece.
• Tapered work can also be carried out.

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Cylindrical Grinding Cont.
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• Machining processes used to produce cylindrical
  surfaces include
• Parallel turning, Cylindrical grinding, Drilling,
  Reaming, Boring, Milling.

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Safety features on a Pedestal Grinder

• A face guard is supplied with the machine to
  protect against grinding debris.
• Easily accessible switches allow the machine to
  be turned off quickly.
• Modern machines are designed to stop quickly.
• The machine should be firmly attached to the
  ground.

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Milling - Industrial Applications

• Milling machines are widely used in the tool and
  die making industry and are commonly used in the
  manufacturing industry for the production of a
  wide range of components.
• Typical examples are the milling of flat
  surfaces, indexing, gear cutting, as well as the
  cutting of slots and key ways.

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Typical Applications.
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Milling Processes.

• Milling is a metal removal process by means of
  using a rotating cutter having one or more
  cutting teeth.

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Milling Processes Cont.

• Cutting action is carried out by feeding the
  workpiece against the rotating cutter.
• Thus the spindle speed the table feed the depth
  of cut and rotation direction of the cutter
  become the main parameters of the process.

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Milling

• Milling is the machining of a surface using a
  cutter which has a number of teeth. A flat
  surface may be produced or special cutters can be
  used to form profiled surfaces.
• The most common type of milling machine is the
  knee and column type.
• The spindle is fixed in the column or main body
  and the table is mounted on a knee.

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Main Parts

• Base cast iron base houses the cutting-fluid
  reservoir and has a rigid construction to prevent
  vibration.
• Column mounted on the base, the column contains
  the spindle.
• Knee allows for vertical movement of the table.
• Saddle provides transverse movement of the
  table.
• Table work pieces and work holding equipment are
  located and clamped.
• Spindle provides the drive for the milling
  cutters

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Types of Milling Machines.

• Most of the milling machine are constructed of a
  column and knee type structure and they are
  classified into two main types namely Horizontal
  milling machine and Vertical milling machine.

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Horizontal Type
Milling cutters are mounted on the arbour.
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• The main spindle is mounted horizontally near the
  top of the column.
• The machine capacity is determined by the maximum
  distance from the table to the spindle as well as
  working surface size and travel in all
  directions.
• The milling cutters have a hole in them in order
  to be mounted on an arbour.
• The cutters are usually large in diameter and are
  found in a range of types including slab, side
  and face, saw, angle and form cutters

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Vertical Type
Variety of cutters can be used
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• The spindle is mounted vertically in a head at
  the top of the column.
• The milling cutters are generally mounted in a
  chuck.
• There are a range of end mills, slot drills and
  profiled cutters (angle, ball-nose, dovetail,
  tee-slot, corner-rounding, etc.)

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Milling Cutters

• Milling tools are highly diverse.
• An end mill is the term used for the tools shown
  below.
• These are the most common types of milling
  cutters and they are used for cutting horizontal
  as well as vertical surfaces.

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Cutting Tools

• Cutting tools for horizontal milling.
• Slab mills.
• For heavy cutting of large and flat surfaces.

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Side and Face Cutters

• Side and face cutters.
• This type of cutting edges on the periphery an
  sides of the teeth for cutting shoulder and
  slots.

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Slitting Saws

• Slitting saws.
• For cutting deep slots or for parting off.

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Cutting tools for vertical milling.

• End mills
• Commonly used for facing, slotting and profile
  milling.

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Rough Cut End Mills

• Rough cut end mills.
• For rapid metal removal.

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Face Milling Cutters

• Face milling cutters.
• For heavy cutting.

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CHUCK MOUNTED CUTTERS
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Milling Arbor Cutters
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Up Cut Milling

• The conventional milling method. In this process
  the milling cutter is rotating against the
  direction of the workpiece.
• There is a danger of the workpiece lifting out of
  the vice, therefore effective clamping is
  necessary.
• A smoother cuttingaction is achieved.

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Up Cut Milling
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DOWN CUT MILLING

• The milling cutter rotates in the same direction
  as the workpiece movement, it is also known as
  climb milling.
• A blacklash eliminator should be fitted to the
  machine for this type of milling to allow heavier
  cuts to be taken without the tendency to lift.
• It produces a finish with less defined cuter
  marks.

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Down Cut Milling
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Typical Milling Operations.

• Face Milling This is using the cutter at right
  angles to the cutting surface. The face or end of
  the cutter generates the desired surface on the
  piece. Many of these cutters are chuck mounted.

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End Milling.

• End milling is the milling of a flat surface
  with the axis of the cutter perpendicular to th
  machining surface.

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Gang millilng.

• Gang milling is a horizontal milling operation
  that utilises three or more milling cutters
  grouped together for the milling of a complex
  surface in one pass.

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Straddle Milling

• Straddle milling When the cutters are mounted on
  the arbour and are separated by spacing collars
  this is known as straddle milling.

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Milling

• These machines are capable of movement in the
  longitudinal, transverse and vertical directions

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Milling set up.

• Correct use of holding devices and a good set up
  are crucial importance in achieving a safe
  accurate and efficient operation of the machine .
• Large workpiece can be mounted directly onto the
  machine table by means of tenons and screws while
  small workpieces are usually held by a machine
  vice.

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Milling Safety.

• Emphasize should be given that the eyes of the
  machine operator must be protected by wearing a
  face shield to prevent accident that may be
  caused by chips, cutting fluid, and tool
  breakage.
• Machine operators must also take care of their
  body such as fingers which should be kept out of
  any moving parts, especially the rotating cutter
  of the machine, to prevent any unnecessary
  accidents or hurt.

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• Peripheral Milling is producing a finished
  surface from the cutting action of the teeth on
  the periphery of the cutter. Up cut and down cut
  milling are examples of peripheral milling

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Climb vs. Conventional Milling

• When milling, one should be aware of the
  difference between conventional,and climb
  milling.
• In conventional milling, the workpiece is fed
  into the rotation of the cutter. This type of cut
  requires lower forces and is preferred for
  roughing cuts.
• In climb milling, the work moves with the
  rotation of the cutter. This produces a better
  finish. It is not recommended if the workpiece
  cannot be held securely or cannot support high
  forces.

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CLIMB V CONVENTIONAL

• CLIMB V CONVENTIONAL

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MOUNTING MILLING CUTTERS

• The two main ways to mount milling cutters are
• (1) Chuck mounted cutters
• (2) Arbour mounted cuters

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Milling Cutter Collets

• The collet of a mill is critical for holding the
  work piece and for easily releasing it. Below are
  shown three types of collets and a cut-away of a
  collet.

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THE DIVIDING HEAD

• Dividing head This is used to hold work so that
  it can be rotated accurately for machining
  specific increments(indexing) e.g splines on
  shafts.

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The Shaping Machine

• The diagram shows details of a quick return
  mechanism as used on the shaping machine.
• The slotted link mechanism allows the ram to
  return on its idle stroke quicker than it takes
  to complete a cutting stroke.
• The length of stroke is altered by moving the
  crankpin location relative to the centre of the
  slotted wheel.

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Shaping Machine Cont.

• The maximum stroke is set by locating the pin at
  the farthest point from the centre
• The angle through which the bull wheel rotates on
  the cutting stroke is larger than the angle of
  the return stroke.
• The ram will therefore move slower on the cutting
  stroke and faster on the return stroke.

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Shaping Machine Operations.
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How the Shaping Machine Works.
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Quick Return Mechanism.

• A quick return mechanism such as the one seen
  opposite is used where there is a need to convert
  rotary motion into reciprocating motion.
• As the disk rotates the black slide moves
  forwards and backwards.
• Many machines have this type of mechanism.

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CNC MACHINING
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CNC MACHINING

• Safety features incorporated in CNC lathes
• Machine will not operated without gaurds in place
  
• Emergency stop button
• Allows for pre machining simulation
• Clear machine guard.

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C.N.C. Terms.

• Time dwell This is the code entered if the
  operation requires a time period to execute a
  tool change. (G04)
• A canned cycle enables a required number of
  repetitive operations to be carried out by a
  single programmed line (block) e.g (G80)

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C.N.C. Terms Cont.

• G-Codes control the cutting movement of the tool.
  M-Codes control operation functions. E.g. M04
  starts the spindle in
• Linear interpolation is the movement of the
  cutting tool while cutting in a straight line.
  E,g GO I

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C.N.C. Terms Cont.

• Stepper motor This is a special motor that runs
  on electrical pulses andturns a fraction of a
  revolution for each pulse, it is used on CNC
  machines.
• A canned cycle is a cnc programme cycle that will
  repeat a process at required amount of times.

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C.N.C. Terms Cont.

• The X-axis is the horizontal axis running
  perpendicular with the machine axis. The cross
  slide movement.
• The z-axis is the vertical axis running parallel
  with the machine axis
• G-codes are programme codes for cnc machining
  that control the movement of the cutting tool.
  Examples would be GOO, GO 1, G99.

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C.N.C. Terms Cont.

• Computer numerical control machining is suitable
  for large quantities of the same part. The
  operator has little involvement. High quality is
  produced
• Conventional machine requires large levels of
  operator input. The operator moves the tool
  manually. This can lead to Inaccuracies in mass
  production.

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C.N.C. Terms Cont

• CAD Computer Aided Design/Drawing/Drafting is
  the process of inputting design data in a system
  with a graphical output.
• CAM Computer Aided Manufacture uses the CAD
  output to produce components in a variety of
  computerised machines including lathe, milling
  machines, etc.

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C.N.C. Terms Cont

• Tool park position is the place where the tool is
  set in order to start a machining operation.
• G00 is a code to inform to move as quickly as
  possible as the machine is not involved in a
  cutting operation.

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Areas of Manufacturing where Robots Are Used

• Aerospace
• Automotive manufacturing and supply
• Chemical, rubber and plastics manufacturing
• Electrical and electronics
• Entertainment-movie making
• Food stuff and beverage manufacturing
• Glass, ceramics and mineral production
• Printing
• Wood and furniture manufacturing

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Specific Robotic Tasks In Manufacturing

• Assembling products
• Handling dangerous materials
• Spraying finishes
• Inspecting parts, produce, and livestock
• Cutting and polishing
• Welding

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Advantages of Robotics

• Competitive Advantage
• Robots can do some things more efficiently and
  quicker than humans.
• Mechanical
• Robots never get sick or need to rest, so they
  can work 24 hours a day, 7 days a week.
• Greater output per hour with consistent quality
• Continuous precision in repetitive operation
• Robots don't get bored, so work that is
  repetitive and unrewarding is no problem.

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Limitations of Robotics

• Today's robots
• Are not creative or innovative
• Can not think independently
• Can not make complicated decisions
• Can not learn from mistakes
• Can not adapt quickly to changes in their
  surroundings
• Every successful business must depend on real
  people for these abilities.

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WORKING ENVELOPE OF ROBOT

• A robot's work envelope is its range of movement.
•  It is the shape created when a manipulator
  reaches forward, backward, up and down.
• These distances are determined by the length of a
  robot's arm and the design of its axes.
• Each axis contributes its own range of motion.

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Factors that influence surface finish when
parallel turning.

• Use of cutting fluids or coolant
• Workpiece material
• Cutting speed
• Sharp and well supported cutting tool.

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Types of Screw Threads.
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Thread Terminology Cont.
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ACME Screw Thread Profile Used in Lathe Laed Screw
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Square Thread Used in Linear Jacks and Clamps
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BUTTRESS THREAD
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Cutting Fluids.

• Cutting Fluids are important in metal cutting
  because they reduce friction, cool the work and
  flush away the chips cut by the tool.

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ADVANTAGES OF CUTTING FLUID

• Cutting fluids have the following benefits
• 1. They cool the cutting tool and work
• 2. They reduce friction by lubricating the tool
  and chip
• 3. They wash away swarf
• These benefits prolong tool and machine life as
  well as reducing power consumption.

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Cutting fluids in common use.

• Water
• It has a high specific heat but is poor in
  lubrication and also encourages rusting. It is
  use as a cooling agent during tool grinding.
• Soluble oils.
• Oil will not dissolve in water but can be made to
  form an intimate mixture or emulsion by adding
  emulsifying agents. The oil is then suspended in
  the water in the form of tiny droplets. These
  fluids have average lubrication abilities and
  good cooling properties.

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• Mineral oils.
• They are used for heavier cutting operations
  because of their good lubrication properties and
  are commonly found in production machines where
  high rates of metal removal are employed. Mineral
  oils are very suitable for steels but should not
  be used on copper or its alloy since it has a
  corrosive effect.
• Vegetable oils.
• They are good lubricants but are of little used
  since they are liable to decompose and smells
  badly.

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Effects of Cutting Fluids when Machining.

• The primary functions of cutting fluids in
  machining are
• Lubricating the cutting process primarily at low
  cutting speeds
• Cooling the workpiece primarily at high cutting
  speeds
• Flushing chips away from the cutting zone

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• Secondary functions include
• Corossion protection of the machined surface
• enabling part handling by cooling the hot surface
• Process effects of using cutting fluids in
  machining include
• Longer Tool Life
• Reduced Thermal Deformation of Workpiece
• Better Surface Finish (in some applications)
• Ease of Chip and Swarf handling

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Safety Hazards associated with Cutting Fluids.

• Skin irritation or dermatitis.
• Staining of work especially aluminium
• Some give off hazards i.e. rancid smells.
• Some create a mist or smoke making work area
  hazardous with toxic fumes.
• Some leave an oily film on work needing extensive
  cleaning by solvents.

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Safety Hazards associated with Cutting Fluids
Cont.

• Irritant effects are caused from contact with
  toxic materials. This can cause industrial
  dermatitis, cracking and soreness of the skin.
  Oils, cutting fluids and fluxes are common
  causes.
• Example - Dermatitis Cracking Skin

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Factors that influence surface finish when
parallel turning.

• Use of cutting fluids or coolant
• Workpiece material
• Cutting speed
• Sharp and well supported cutting tool.

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Types of Screw Threads.
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Thread Terminology Cont.
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ACME Screw Thread Profile Used in Lathe Laed Screw
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Square Thread Used in Linear Jacks and Clamps
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BUTTRESS THREAD
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Surface Finish.

• Factors which influence surface finish
• The material being machined
• The cutting speeds used.
• The sharpness of the cutting tool

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Machinability.

• Machinability is a measure of how easy or
  difficult it is to cut a material.
• The following can be used to determine
  machinability.
• Tool life weak materials long tool life
  good machinability.
• Cutting forces low cutting forces good
  merchantability.
• Surface finish good surface finish good
  machinability.

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MEASURING METHODS

• Direct measurements are determined using a
  measuring instrument such as a ruler and the
  scale on the ruler is matched with the component

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INDIRECT MEASURMENT
126
Measuring Methods Cont.

• Comparative measurement is when gauges are used
  to compare the size of the component with that of
  the gauge
• Absolute dimensions. All dimensions are taken
  from the outside end of work piece,
• Incremental Dimensions. All dimensions are taken
  from the previous Position and not from a fixed
  datum.

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Reasons why imprecise measurements may be taken
from measuring tools.

• Burrs or scratching on precision equipment.
• Human error.
• Staining or rough use of equipment.
• Damaged precision equipment.

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Interference and Clearance Fits

• Interference Fit.
• If the limits of the shaft are always larger than
  the limits of the hole an interference fit
  occurs.
• Clearance Fit.
• If the limits of the shaft are always smaller
  than the limits of the hole a clearance fit
  occurs.

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Interference and clearance
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Gauging

• Gauging is where specific precision gauges are
  used to check and compare dimensional accuracy.
• Examples include no go and go Plug and gap
  gauges, telescopic gauges, and screw pitch
  Gauges.
• Direct measurement requires more skill in setting
  and directly reading, micrometers and precision
  vernier callipers would be examples

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MEASURING GAUGES

• The gauge is a PLUG gauge. It accurately
  determines if a hole is drilled to within its
  tolerance.

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Gap Gauge

• The gauge is a Gap gauge. Its function is to
  check if the size of a component is within it
  tolerance
• Spark plug using gap gauge

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SCREW PITCH GAUGE

• Screw pitch gauge. This gauge is used to check
  the pitch of screw by placing the blade that fits
  the best on a screw to determine the pitch size.

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SINE BAR

• This is used to set up and measure angles
  accurately.

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THE SINE BAR

• The sine bar is a precision measuring instrument
  used to measure angles accurately.
• By using trigonometry, Gauge blocks and knowing
  the centre distances, (usually they come in
  distances of 100mm, 200mm, 250mm and 300mm )
  between the rollers which are of a set diameter.

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SLIP GAUGES

• Slip Gauges have very accurate measuring faces,
  flat and parallel to each other. They are usually
  rectangular in shape. They have two very flat
  parallel surfaces at opposite ends.

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TELESCOPIC GAUGES
There are a range of gauges that are used to
measure a bore's size, by transferring the
internal dimension to a remote measuring tool.
They are a direct equivalent of inside calipers
and require the user to develop the correct feel
to obtain repeatable results
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TELESCOPIC GAUGES
Telescoping gages need to be rocked over center
to size and center the telescoping gage
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VERNIER CALLIPERS
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HOW TO USE VERNIER CALLIPERS?
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COMPARATORS

• Comparators are used to compare the sizes of
  components. A simple comparator could consist of
  a dial gauge fixed to a stand.
• Comparisons can be made quickly if the dial gauge
  is first set to zero using slip gauges to the
  required height.

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PRECISION BALLS

• Precision Balls make it possible to take linear
  measurement across angles, in order to calculate
  the angle.

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• SCREW CUTTING GAUGE
• This is used when grinding screw cutting tools to
  ensure that the tool angles recorrect for the
  type of thread being cut. E.g. I.S.0 thread 60
  degrees.

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Height gauge

• Provides an accurate method of marking out
  metals and plastics.
• Relatively easy to use once reading a vernier
  scale is mastered.
• Can be used with vee blocks on round materials.
• Can have a digital readout for increased accuracy.

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CUTTING TOOL GEOMETRY

• The shear plane will affect the depth of cut and
  hence the amount of power used in the cutting
  process.
• A large shear plane will give a large depth of
  cut or chip thickness while a small shear plane
  will give a small depth of cut.

146
CUTTING TOOL FORCES

• Orthogonal cutting has two forces. The tangential
  force and the axial force acting on the tool
  during cutting
• Oblique cutting has three forces acting on the
  cutting tool. The tangential force, the axial
  force and the radial force. This force is caused
  by the plan approach angle on the cutting tool.
  The axial forces decrease as the radial forces
  increase.

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Orthogonal Cutting
148

• Oblique Cutting has three forces acting on the
  cutting tool.
• The tangential force, the axial force and the
  radial force.
• This force is caused by the plan approach angle
  on the cutting tool.
• The axial forces decrease as the radial forces
  increase

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Oblique Cutting
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TOOL GEOMETRY CONT.

• A large rake angle gives a small shear area hence
  easy to cut
• A small rake angle gives a large shear area and
  therefore more difficult to cut.

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DYNAMOMETER

• Used for measuring tool cutting forces

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Workholding Methods

• The four-jaw independent chuck has four
  independent jaws that are adjusted individually
  from each other, they are also reversible.The
  four jaw is used to hold square, rectangular and
  irregular shapedWork pieces that cannot be used
  in a self-centring chuck.

153
Workholding Cont.

• The Three Jaw operates differently by means of a
  pinion engaging with a gear. Each jaw is numbered
  and must be inserted in the correct order All
  three jaws moved simultaneously and automatically
  centre up the work. It is used for circular or
  hexagonal pieces.

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The Magnetic Chuck.
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Collets

• Collets are very precise but must be used on work
  which is the same diametere as the inside of the
  collect.
• A set of different size collets is normally
  required.

156
Holding Long Work.

• The Fixed Steady
• The fixed steady is clamped in the lathe bed and
  supports the work close to where the tool is
  cutting.

157
The Travel Steady

• The travailing steady is clamped to the saddle
  and supports the work close to where the tool is
  cutting.

158
Mandrel

• Use to hold long bars

159
FORMING AND GENERATING SURFACES

• Forming, When the surface produced is a copy of
  the tool producing it, it is referred to as
  forming.. e.g. Screw cutting, u-cutting and
  contour work. Forming uses a specially designed
  cutting tool, which is in the shape of the shape
  to be cut. The tool is then forced directly into
  the work.
• EG Parting Off Tool

160
Generating a Surface

• Generating. By moving the tool in various
  directions until the required surface is
  machined. In generating the cutting tool is a
  single point cutter, which follows the path of
  the shape to be cut. ego facing, surfacing. taper
  turning.
• e.g. taper-turning using the compound slide.

161
Basic Metal Cutting.

• The usual conception of cutting suggests clearing
  the substance apart with a thin knife or wedge.
• When metal is cut the action is rather different
  and although the tool will always be wedge shaped
  in the cutting area and the cutting edge should
  always be sharp the wedge angle will be far too
  great for it to be considered a knife shape.
• Consequently a shearing action takes place when
  the work moves against the tool.

162
Tool Angles.

• There are three important angle in her
  construction of a cutting tool rake angle,
  clearance angle and plan approach angle.

163
Rake Angle.

• Rake angle is the angle between the top face of
  the tool and the normal to the work surface at
  the cutting edge. In general, the larger the rake
  and the smaller the cutting force on the tool
  since for a given depth of cut the shear plane.
• A large rake angle will improve cutting action
  but would lead to early too failure, since the
  tool wedge angle is relatively weak. A compromise
  must therefore be made between adequate strength
  and good cutting action.

164
Clearance Angle.

• Clearance angle is the angle between the flank or
  front face of the tool and a tangent to the work
  surface origination at the cutting edge.
• All cutting tools must have clearance to allow
  cutting to take place.
• Clearance should be kept to a minimum, as
  excessive clearance angle will not improve
  cutting efficiency and will merely weaken the
  tool.
• Typical value for front clearance angel is 6
  degrees in external cutting.

165
RAKE CLEARANCE ANGLE
166
Cutting Tool Materials.

• Hot hardness. This means the ability to retain
  its hardness at high temperatures. All cutting
  operations generate heat, which will affect the
  tools hardness and eventually its ability to cut.
  
• Strength and resistance to shock. At the start of
  a cut the first bite of the tool into the work
  results in a considerable shock loading on the
  tool. It must obviously be strong enough to
  withstand it.

167
CHIP FORMATION

• Continuous chip,
• Discontinuous chip,
• Discontinuous chip with built up edge.

168
CONTINUOUS CHIP

• A continuous chip is formed when a ductile metal
  such as aluminium or steel is machined. A
  discontinuous chip is formed when brittle
  materials such as brass or cast iron are machined.

169
Discontinuous Chip

• The chip leaves the tool as small segments of
  metal resulted from cutting brittle metals such
  as cast irons and cast brass with tools having a
  small rake angle
• There is nothing wrong with this type of chip in
  these circumstances.

170
Built Up Edge

• Chip with built up edge Very rough surface on
  the underside of the chip and also on the
  machined surface of the work. Caused by
  continuous chip and can be prohibited by the use
  of coolant to prevent particles of the work being
  welded to the tool face. .

171
Chip Breaker

• A chip breaker is used to break the continuous
  chip into sections so that the chip cannot tangle
  around the cutting tool. The simplest form of
  chip breaker is made by grinding a groove on the
  cutting tool face a few millimeters behind the
  cutting edge.

172
Cutting Speed Feed.

• The relative speed of work piece rotation and
  feed rates of the cutting tool coupled to the
  material to be cut are very important.

173
Spindle Speed

• Spindle speed in revolutions per minute (R.P.M.)
  for the cutter can be calculated from the
  equation.
• CS X 1000
• N d
• Where N R.P.M.
• Cs

174
Low Coefficient of Friction.

• Value which describes the ratio of the force of
  friction between two bodies and the force
  pressing them together.
• The coefficient of friction depends on the
  materials used for example, ice on steel has a
  low coefficient of friction, while rubber on
  pavement has a high coefficient of friction.
  Coefficients of friction range from near zero to
  greater than one under good conditions

175
Tool Materials in Common use.

• High carbon steel.
• Contains 1 1.4 carbon with some addition of
  chromium and tungsten to improve wear resistance.
  The steel begins to lose its hardness at about
  250degrees and is not favored for modern
  machining operations where high speeds and heavy
  cuts are usually employed.

176
High Speed Steel.

• Steel, which has a hot hardness value of about
  600dc possesses good strength and shock resistant
  properties. It is commonly used for single point
  lathe cutting tools and multi point cutting tools
  such as drills, reamers and milling cutters.

177
Cemented Carbides.

• An extremely hard material from tungsten powder.
• Carbide tools are usually used in the form of
  brazed or clamped tips.
• High cutting speeds may be used and material
  difficult to cut with HSS may be readily
  machined using carbide tipped tools.

178
Tool Life.

• As a general the the relationship between the
  tool life and cutting speed is
• VTn C
• Where V Cutting speed in r/min
• T Tool life in minutes.
• C Constant.
• For high speed steels tools are value of C ranges
  from 0.14 to 0.1 and for carbide bits the value
  would be 0.2.

179
Prolonging Tool Life

• Use cutting fluids when machining.
• Choose suitable cutting tools for each machining
  process.
• Run the machine at the correct speed to prevent
  heat build-up.
• Ensure that the machine is in good condition and
  not prone to excessive vibration.
• Use the correct cutting speed and cutting feed
  for the material.

180
Feed.

• The term feed is used to describe the distance
  the tool moves per revolution of the work piece
  and depends largely on the surface finish
  required.
• For a roughing out a soft material a feed of up
  to 0.25mm per revolution may be used.
• With tougher material this should be reduced to a
  maximum of 0.1mm/rev.
• Finishing requires a finer feed than what is
  recommended.

181
Safety Hazards When Machining Mild Steel.

• Excessive heat may cause deformation of cutting
  tool.
• The hardness of mild steel may cause tool wear.
• Discontinues chips may be excessively sharp and
  hot.

182
Factors that influence heat in machining

• Factors that influence heat in machining
• Use of coolants help to reduce heat generated
• Type of material
• Machining operation
• Condition of machine and cutting tool.