Metrology- Slip gauge, Dial indicator, Bevel protractor, Sine bar, Angle gauge

METROLOGY

  • Metrology is the science of measurements.
  • In manufacturing industry the dimensions are measured to control the shape and sizes of an object
  • Controlled measurements are necessary in the manufacture of interchangeable parts

Linear Measuring Instruments

  • Slip gauges
  • Dial indicator

Angle Measuring Instruments

  • Bevel Protractor
  • Sine bar
  • Angle gauge

Slip gauges

  • Slip gauges are used for precise measurement of parts and for verifying measuring tools such as micrometers,comparators and various limit gauges
  • Slip gauges are rectangular blocks made of alloy steel having a cross-section of about 32mm by 9mm
  • The distance between two opposite faces determines the size of the gauge
  • During use, the required number of gauge blocks are used together to know the required dimension.

Dial Indicators

  • Dial indicators are used to test and inspect the size and trueness of a finished work
  • It is measured to an accuracy of 0.01mm
  • They are also used in conjunction with other measuring instruments like inside calipers,Depth gauges etc to measure inside and out side dimensions,errors in parallelism,flatness etc

Bevel protractor

  • A Bevel protractor is used to check angles up to an accuracy of 5min
  • It consists of a protractor disc carrying degrees,reading from 0 to 90degrees on either side of an arc
  • It is free to rotate about fulcrum and can be clamped at a desired angle with a nut
    •  The vernier scale on the disc has 12 equal divisions over a space of 23 degrees on the main scale
    • One division of vernier scale is equal to 23/12
    • The difference between two divisions of main scale and one division of vernier scale is 5min

To read the instrument :

  • Note the whole degrees between zero of main scale and zero on vernier scale
  • In the same direction,note the division line of vernier scale which coincides with any division line of main scale
  • Multiply the number by 5 to give number of minutes to be added to whole degrees
  • As an example from the fig
      • The whole degrees on main scale between zero of vernier and zero of main scale is 17° and 5th division of vernier scale coincides with any division of main scale
      • The measure of angle will be 17+5'x 5=17°25'

Sine Bar





  • Sine bar used for measuring and setting angles
  • It has two hardened steel rollers of equal diameter fastened near the ends
  • The axis of rollers are mutually parallel and the centers of these cylinders are on a line exactly parallel with the working face of the bar
  • It is used on surface plate in conjunction with a set of slip gauges
  • A sine bar is specified by the distance between the centers of two rollers
  • From the fig. angle can be obtained by trigonometry
  • Sinø =height of slip gauges(H) / central distance of rollers( L)

Angle gauge

  • The angle gauges are used for measuring and setting out angles in the work shops
  • Angle gauges are measured to an accuracy of 3sec
  • These are wedge shaped steel blocks and their working faces are finished in the same manner as slip gauges
  • The angle blocks can be wrung together as in slip gauges
  • A set of angle gauges consists of 12 separate gauges
  • These are used in conjunction with precision square block to setup any angle between 0 to 360°
  • These gauges are available in 3 series
  • Degree series,1°,3°,9°,27°and 41°
  • Minute series 1min,3min,9min and 27min
  • Fraction of minute series 0.1min,0.3min,and 0.5min

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