Unit 4: Standard of Measurements
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Questions and Answers

What is the fundamental unit of linear measurement widely accepted worldwide?

  • Metre (correct)
  • Foot
  • Inch
  • Yard

    • What is the issue with material standards used earlier?

  • They change their size with temperature and other conditions (correct)
  • They are not widely used
  • They are not precise
  • They are not accurate

    • What is the natural and invariable unit for length?

  • Wavelength of monochromatic light (correct)
  • Distance between two lines
  • Length of a ruler
  • Length of a metal bar

    • What is the definition of a yard or metre?

    <p>The distance between two scribed lines on a bar of metal</p> Signup and view all the answers

    What is the type of measurement used when measuring between two lines?

    <p>Line standard</p> Signup and view all the answers

    What is the type of measurement used when measuring between two flat parallel surfaces?

    <p>End standard</p> Signup and view all the answers

    What is the main challenge in making measurements?

    <p>Skill of the operator and time-consuming process</p> Signup and view all the answers

    What is the main reason for variations in manufacturing processes?

    <p>Natural variability</p> Signup and view all the answers

    What is the term for the difference between the upper and lower limits of a dimension?

    <p>Permissive tolerance</p> Signup and view all the answers

    What is the purpose of controlling assignable causes in manufacturing?

    <p>To achieve consistent production and design requirements</p> Signup and view all the answers

    What is the main reason for allowing tolerances in manufacturing?

    <p>To accommodate natural variability in production processes</p> Signup and view all the answers

    What is the basic size of a shaft with a diameter of 40 ± 0.02 mm?

    <p>40 mm</p> Signup and view all the answers

    Why is a rule not suitable for direct measurement of the distances between two edges?

    <p>Because it is a line-measuring device</p> Signup and view all the answers

    What is the main purpose of interchangeability in manufacturing?

    <p>To enable easy replacement of defective parts</p> Signup and view all the answers

    What is the main reason for undersizing in line standards?

    <p>Wear on the leading ends</p> Signup and view all the answers

    What is the advantage of end standards over line standards?

    <p>They are more accurate</p> Signup and view all the answers

    What type of interchangeability involves parts manufactured at different locations?

    <p>Universal interchangeability</p> Signup and view all the answers

    What is the purpose of wringing groups of blocks or slip gauges together in end standards?

    <p>To create the required size</p> Signup and view all the answers

    Why is it necessary to specify tolerances in manufacturing?

    <p>To permit dimensional variations in components</p> Signup and view all the answers

    What is the maximum dimensional tolerance that can be obtained with end standards?

    <p>±0.0005 mm</p> Signup and view all the answers

    What is the definition of tolerance in manufacturing?

    <p>The magnitude of permissible variation of a dimension</p> Signup and view all the answers

    What is the advantage of interchangeable manufacture?

    <p>Increased productivity and reduced production time costs</p> Signup and view all the answers

    Why is it necessary to initially calibrate end and line standards at 20 ± ½ ºC?

    <p>To minimize the effect of temperature changes on accuracy</p> Signup and view all the answers

    Why is it important to follow common standards in manufacturing?

    <p>To achieve universal interchangeability</p> Signup and view all the answers

    What is the primary purpose of providing enough clearance between the shaft and the hole?

    <p>To maintain an oil film for lubrication purpose</p> Signup and view all the answers

    Why is it not possible to manufacture a part to the exact size in mass production?

    <p>Due to the inherent inaccuracy of manufacturing methods</p> Signup and view all the answers

    What is the percentage of parts that will be within ±3s limits of the mean value if the process is kept under control?

    <p>99.74%</p> Signup and view all the answers

    What is the primary advantage of interchangeable manufacture?

    <p>Increased productivity with a corresponding reduction in manufacturing cost</p> Signup and view all the answers

    What is the main requirement for interchangeable assembly?

    <p>The dimensions of the components must be confined within the permissible tolerance limits</p> Signup and view all the answers

    What is the primary goal of mass production?

    <p>To produce identical components with a high degree of accuracy</p> Signup and view all the answers

    What is the primary criterion for specifying tolerance limits?

    <p>Functional requirements</p> Signup and view all the answers

    What is the purpose of limits in manufacturing?

    <p>To ensure parts fit and function correctly</p> Signup and view all the answers

    What is the definition of tolerance?

    <p>The difference between the upper and lower limits</p> Signup and view all the answers

    What type of fit is used where easy assembly and disassembly are required?

    <p>Clearance Fit</p> Signup and view all the answers

    What is the purpose of the ISO system of limits and fits?

    <p>To combine letters and numbers to define fits</p> Signup and view all the answers

    What type of gauge is used to check the dimensions of holes?

    <p>Plug Gauges</p> Signup and view all the answers

    What is the purpose of Go Gauges?

    <p>To check the lower limit</p> Signup and view all the answers

    What is the classification of fits based on?

    <p>The relationship between mating parts</p> Signup and view all the answers

    What is the purpose of gauges in manufacturing?

    <p>To ensure quality control</p> Signup and view all the answers

    What is the definition of a Transition Fit?

    <p>There can be either a slight gap or a slight interference between the mating parts</p> Signup and view all the answers

    Study Notes

    Standard of Measurements

    • Two standard systems for linear measurement: English (yard) and metric (metre) systems
    • The metric system is widely accepted and used as the fundamental unit of linear measurement
    • Scientists have always sought a suitable unit for length that remains constant regardless of environmental conditions
    • The wavelength of monochromatic light is used as a natural and invariable unit for length

    Line and End Measurements

    • Line standard: measures distance between two engraved lines
      • Examples: yard and metre
      • Used for quick and easy measurements
      • Limited accuracy (±0.2 mm) and requires magnifying lens or microscope for high accuracy
    • End standard: measures distance between two flat and parallel surfaces
      • Examples: slip gauges, end bars, and micrometer anvils
      • Used for precision measurements in workshops and laboratories
      • High accuracy (up to ±0.0005 mm) and requires skill and time for measurement

    Characteristics of Line Standards

    • Quick and easy measurements
    • Limited accuracy (±0.2 mm)
    • Engraved lines have thickness, making high accuracy measurements difficult
    • Markings on the scale are not subjected to wear, but leading ends may wear, resulting in undersizing
    • No built-in datum, making alignment difficult
    • Subject to parallax effect, leading to reading errors

    Characteristics of End Standards

    • High accuracy (up to ±0.0005 mm)
    • Measurements are time-consuming and require skill
    • Measuring surfaces are subjected to wear
    • Built-in datum, making alignment easy
    • Not subject to parallax error

    Comparison between Line and End Standards

    • Line standards: quick and easy, but limited accuracy and no built-in datum
    • End standards: high accuracy, but time-consuming and requires skill, with a built-in datum

    Limits, Fits, and Tolerances

    • Manufacturing processes inherently produce variations in size and shape
    • Tolerances: the magnitude of permissible variation in a dimension or measured value
      • Upper limit: maximum allowable dimension
      • Lower limit: minimum allowable dimension
      • Tolerance: difference between upper and lower limits
    • Fits: describe the relationship between mating parts, such as a hole and a shaft
      • Clearance fit: gap between mating parts, used for easy assembly and disassembly
      • Interference fit: overlap between mating parts, used for permanent or semi-permanent assembly
      • Transition fit: slight gap or overlap, used for accurate location and moderate tightness

    Principle of Interchangeability

    • Manufacture of identical parts in bulk, allowing for interchangeable assembly
    • Essential for mass production and modern manufacturing techniques
    • Enables the production of components with a desired fit, without further modification during assembly
    • Increases productivity, reduces manufacturing cost, and facilitates ease of replacement

    Tolerances

    • Essential for manufacturing products with a desired level of accuracy and quality
    • Tolerance principles: permit dimensional variations, achieve interchangeable assembly, and ensure functional requirements
    • Tolerance is an absolute value, defined as the algebraic difference between the upper and lower acceptable dimensions
    • Industry follows approved accuracy standards, such as ANSI and ASME, to manufacture different parts### Tolerances
    • A letter indicates the fundamental deviation (position of tolerance zone relative to nominal size)
    • A number indicates the tolerance grade (size of tolerance zone)

    Basis Systems

    • Hole Basis System: hole is kept as basic size, shaft size is varied to get desired fit
    • Shaft Basis System: shaft is kept as basic size, hole size is varied to get desired fit

    Gauges

    • Essential for quality control in manufacturing processes
    • Used to measure dimensions of manufactured parts and ensure conformity to specified limits

    Types of Gauges

    • Limit Gauges:
      • Check whether part's dimension falls within specified limits
      • Go Gauge: checks lower limit, part should fit into or pass through
      • No-Go Gauge: checks upper limit, part should not fit into or pass through

    Plug Gauges

    • Cylindrical gauges used to check dimensions of holes
    • Go Plug Gauge: should fit into hole
    • No-Go Plug Gauge: should not fit into hole

    Ring Gauges

    • Used to check dimensions of shafts
    • Go Ring Gauge: shaft should fit into ring
    • No-Go Ring Gauge: shaft should not fit into ring

    Snap Gauges

    • Used to check external dimensions of cylindrical parts, such as shafts
    • Go Snap Gauge: part should pass through
    • No-Go Snap Gauge: part should not pass through

    Limits and Fits

    • Limits: define permissible variations in dimensions to ensure parts fit and function correctly
    • Fits: describe relationship between mating parts, ensuring correct assembly (clearance, interference, and transition fits)

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    Description

    Explore the two standard systems for linear measurement, including the English and metric systems, and the advantages of the metric system.

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