Engineering

• Rack and Pinion


  A mechanism consisting of a gear (the pinion) that meshes with a toothed bar (the rack). When the pinion rotates, it moves the rack linearly.
• Rack and Pinion


  • Commonly used in steering systems in vehicles, where the rotation of the steering wheel (pinion) converts into linear motion to turn the wheels
• Lever


  A simple machine consisting of a rigid bar (the lever arm) that pivots around a fixed point (the fulcrum)
• Levers


  • Used to amplify force or change the direction of a force
  • Examples include seesaws, crowbars, and scissors
• Gear


  Toothed wheels that mesh with each other to transmit motion and power
• Gears


  • Can change the speed, torque, or direction of rotation
  • Examples include spur gears, bevel gears, and worm gears
• Pulley


  Wheels with a groove around the circumference that is used to guide belts or ropes
• Pulleys


  • Used to transmit motion and force, often to change the direction of force or lift heavy loads
  • Examples include simple fixed pulleys, movable pulleys, and compound pulleys
• Chain and sprocket system


  A mechanical mechanism used to transfer motion and power between two rotating shafts
• Two main Types


  • Thermoplastics
  • Thermosetting Plastics
• Examples of Thermoplastics


  • Acrylic
  • Polythene
  • Nylon
  • PVC
  • Polystyrene
  • Polypropelene
• Examples of Thermosetting plastics

  • Bakelite
  • Melamine
  • Fibre glass resin
• Gearbox


  • Contains a set of pairs of gears with different gear ratios
  • You choose which gears are engaged by sliding the gears on their axles
  • Used in cars & machines to change output speed and direction
• Clutch


  Can be used before a gearbox to allow the gears to be changed smoothly
• Crank


  Converts rotary motion to reciprocating motion, and vice versa
• Slider


  Converts rotary motion to reciprocating motion, and vice versa
• Cam


  Converts rotary motion to reciprocating motion
• Follower


  Changes the angle of rotation by 90 degrees
• Bevel gear


  • Changes the speed
  • Depends on the ratio of teeth in each gear
  • Non-reversible - the worm can turn the worm wheel, but the worm wheel cannot turn the worm
  • High gear ratio: one full rotation of the worm only moves the worm wheel along by one tooth
• Worm drive


  • Raising heavy loads without slipping
  • Reducing motor speed e.g. used in inline motors
• Threading


  The process of creating a screw thread on the outside of a cylinder using a die tool
• Die


  • A circular split die is used to cut external threads on round bars or pipes
  • The thread size is indicated on the top of the split die
  • Made from a hard material like high-speed steel (HSS)
  • A die stock or die holder is used to hold the die during the threading process
• Threading process


  1. Cut the cylinder to the required length

  2. Choose the correct diameter cylinder to match the desired nut
• Peg-and-slot mechanism


  • Converts rotary motion into oscillating motion
  • A peg is rotated via a disc usually connected to a motor or engine
  • The peg fits in to a slot in a shaft
  • The shaft pivots around a fixed fulcrum at one end
  • As the peg rotates, it slides up and down in the slot, rocking the arm left-to-right (and back again) around its fulcrum
• Crank and slider


  Converts rotary motion to reciprocating motion, and vice versa
• Cutting tool


  • Lathes use single-point cutting tools
  • They are usually made from one piece of HSS (high-speed steel), or contain tungsten-carbide inserts
  • Cutting tools must be on-centre before cutting
• Parting-off tool


  • A sharp narrow tool for cutting fully through the workpiece (and separating it into two parts)
  • Can also be used to create undercuts - cylindrical grooves in the workpiece
• Morse taper drill bit


  Have a tapered shank so that can be gripped in the tapered tailstock barrel without the need for a tailstock chuck
• Centre drill


  Used to create a small conical hole in the end of the workpiece, either as a pilot hole for drilling, or so that the workpiece can be supported by a centre held in the tailstock
• Knurling tool


  • Makes a diamond- or other-shaped pattern on the surface of the workpiece
  • Knurling creates a grip surface on metal surfaces
• Parallel turning


  • The workpiece is clamped in the chuck and rotated
  • The cutting tool is fed right-to-left, parallel to the axis of rotation, manually or automatically
  • Long workpieces can be supported using steadies or a tailstock centre
• Facing


  • Produces a flat surface on the end of the workpiece
  • The cutting tool cuts with the front edge
  • The tool is fed inwards only, at right angles to the axis of rotation
• Setting the tool on-centre

  • The cutting edge of the tool must be aligned with the centre axis of the workpiece before machining
  • If the tool is too high, the rake and clearance angles will be incorrect, causing rubbing and poor surface finish
  • If the cutting tool is too low, cutting angles will be affected and the cutting edge cannot reach the centre of the workpiece, leaving an uncut piece
• Parting-off


  • Cutting the workpiece into two pieces by moving a parting-off tool inwards in a straight line, to cut a narrow groove from the surface to the centre
  • The height of the tool must be in line with the centre axis of the workpiece
• Clutch


  • Consists of two plates that can be engaged and disengaged to transmit or stop rotation from one axle to the other
  • Allows a rotating shaft to have a 'bend' or 'hinge' in it, while continuing to rotate
• Universal joint


  Made from two hinges at 90 degrees
• Ball bearings


  Use hard steel balls to reduce friction between the inside (axle) and outside (axle support)
• Roller bearings


  • Use cylindrical rollers instead of balls
  • Quieter than ball bearings, and can support heavier loads
• 1. belt pulley drive


  Uses a V-shaped belt to prevent the belt sliding off the pulley wheels
• Toothed-belt pulley drive


  Uses a toothed belt and gears to prevent the belt slipping around the pulley