Unit 4: Standard of Measurements
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Questions and Answers

What is a major limitation of measurement methods?

  • They are limited to linear measurements
  • They are only suitable for measuring small components
  • They are time-consuming and prone to wear (correct)
  • They require a high level of operator skill

    • What is the primary cause of natural variability in manufacturing processes?

  • Random and uncontrollable causes (correct)
  • Operator error and machine wear
  • Defective raw materials and poor management
  • Improperly adjusted machines and characteristic variability

    • What is the term for variability caused by assignable causes?

  • Characteristic variability (correct)
  • Process variability
  • Natural variability
  • Assignable causes

    • What is the purpose of specifying tolerance limits in manufacturing?

    <p>To allow for some variability in dimension</p> Signup and view all the answers

    What is the difference between the upper and lower limits of a tolerance?

    <p>The permissive tolerance</p> Signup and view all the answers

    What is the basic or nominal size of a component?

    <p>The size based on which dimensional deviations are given</p> Signup and view all the answers

    What is the primary reason for providing clearance between a shaft and a hole?

    <p>To allow an oil film to be maintained for lubrication</p> Signup and view all the answers

    What is the consequence of manufacturing a shaft and hole with zero clearance?

    <p>The shaft will experience excessive force</p> Signup and view all the answers

    What is the ideal condition for achieving a proper fit between a shaft and a hole?

    <p>Specifying a definite size to the hole and varying the shaft size</p> Signup and view all the answers

    What is the probability that a part will fall within 3σ limits of the mean value?

    <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 essential condition 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 main advantage of using end standards over line standards?

    <p>They provide higher accuracy than line standards</p> Signup and view all the answers

    What is the main limitation of line standards that affects their accuracy?

    <p>The engraved lines possess thickness</p> Signup and view all the answers

    What is the purpose of the built-in datum in end standards?

    <p>To provide a reference point for measurement</p> Signup and view all the answers

    What is the effect of temperature changes on line and end standards?

    <p>They influence the accuracy of the measurement</p> Signup and view all the answers

    What is the main difference between the principle of measurement of line and end standards?

    <p>The distance between two engraved lines versus the distance between two flat and parallel surfaces</p> Signup and view all the answers

    What is the advantage of using groups of blocks or slip gauges in end standards?

    <p>They allow for the creation of the required length</p> Signup and view all the answers

    What is the primary standard for length that is not affected by environmental conditions?

    <p>Wavelength of monochromatic light</p> Signup and view all the answers

    Which of the following is a characteristic of the material standards used earlier?

    <p>They change their size with temperature and other conditions</p> Signup and view all the answers

    What is the definition of a yard or metre in terms of a bar of metal?

    <p>The distance between two scribed lines on a bar of metal maintained under certain conditions of temperature and support</p> Signup and view all the answers

    What is the example of line standard?

    <p>The rule with divisions marked with lines</p> Signup and view all the answers

    What is end standard or end measurement?

    <p>The distance between two flat parallel surfaces</p> Signup and view all the answers

    What is the advantage of using the metric system?

    <p>It is more widely accepted and has several advantages</p> Signup and view all the answers

    What is the primary factor that determines the specification of tolerance limits if high performance is the sole criterion?

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

    What is the purpose of fit classification in manufacturing?

    <p>To ensure that parts can be assembled correctly and function as intended</p> Signup and view all the answers

    What is the difference between the Hole Basis System and the Shaft Basis System in the ISO system of limits and fits?

    <p>One keeps the hole as the basic size, while the other keeps the shaft as the basic size</p> Signup and view all the answers

    What is the primary purpose of limit gauges in manufacturing?

    <p>To check whether a part's dimension falls within specified limits</p> Signup and view all the answers

    What is the purpose of a No-Go Gauge in manufacturing?

    <p>To ensure the part does not fit into the gauge</p> Signup and view all the answers

    What is the term for the maximum allowable dimension of a part?

    <p>Upper limit</p> Signup and view all the answers

    What is the purpose of a plug gauge in manufacturing?

    <p>To check the dimensions of holes</p> Signup and view all the answers

    What is the application of a transition fit?

    <p>Where accurate location and moderate tightness are required</p> Signup and view all the answers

    What is the term for the permissible variation in a dimension?

    <p>Tolerance</p> Signup and view all the answers

    What is the purpose of gauges in manufacturing?

    <p>To check whether a part's dimension falls within specified limits</p> Signup and view all the answers

    What is the primary advantage of interchangeable assembly in manufacturing?

    <p>Facilitating ease of replacement of defective parts</p> Signup and view all the answers

    What is the benefit of achieving specialization in labor?

    <p>Reducing production and assembly time</p> Signup and view all the answers

    What is universal interchangeability?

    <p>The ability to assemble parts manufactured at different locations</p> Signup and view all the answers

    What is the purpose of providing tolerances in manufacturing?

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

    What is the definition of tolerance?

    <p>The total variation permitted in the size of a dimension</p> Signup and view all the answers

    What factor influences the choice of tolerances in manufacturing?

    <p>Functional requirements, manufacturing process, cost, and standardization</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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