Diploma Measurements and Metrology Study Material – Unit 3

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We are adding  Diploma Measurements and metrology study material for N Scheme important Questions and answers for the Unit 3 – 3 Marks. Check the link below to download Diploma Measurements and metrology study material pdf & Diploma Measurements and metrology notes

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Subject: Measurements and Metrology                     Scheme: N

Unit 3 – Form Measurement

  1. What is a Screw thread?

A screw thread is a continuous helical groove of specified cross produced on the external or internal surface of a cylinder or a cone

  1. Mention the types of Screw threads.

The screw threads are grouped into two principal classes based on the form of thread

  • Vee threads
  • Transmission threads
  1. Explain root of the srew thread

Root is the bottom of the groove between the sides of two adjacent threads

  1. What is a pitch of a screw thread?

The distance measured parallel to the axis from a point on a thread to the corresponding point on the next (adjacent) thread is called pitch of the thread

  1. Define major diameter.

Major diameter is the diameter of an imaginary co-axial cylinder which would touch the crests of an external thread or roots of an internal thread. Major diameter is also called external diameter or outside diameter

  1. What is a Effective diameter?

Effective diameter is the diameter of an imaginary co-axial cylinder which intersects the flanks of the threads such that the widths of the threads and widths of the spaces between the threads are equal, each being half the pitch

  1. What are the various elements of a screw thread?

The various elements of a screw thread are.

  • Major Diameter
  • Minor Diameter
  • Effective diameter
  • Pitch
  • Flank angles
  • Thread form
  1. Mention the methods of measuring major diameter of external method.

The methods of measuring major diameter of external method are

  • Using ordinary micrometer
  • Using bench micrometer
  1. Name the methods of measuring minor diameter of internal method.

 The methods of measuring major diameter of external method are

  • Using taper parallels
  • Using rollers & slip gauges
  1. What is one wire method?

In one wire method, one wire is placed between two threads at one side and the anvil of the measuring micrometer contacts the crests on the other side.

Diploma Measurements and Metrology Study Material
Diploma Measurements and Metrology Study Material
  1. Explain two wire method

In this method the effective diameter of a screw thread is measured by placing two wires or rod of identical diameter. The wires of suitable sizes are placed between the standard and the micrometer anvils and the first micrometer reading is taken

  1. What is three wire method?

In three wire method, three wires of equal and precise diameter are placed in the thread groves at opposite sides of the screw and measuring the distance M over the outer surfaces of the wires with the micrometer.

  1. What is the purpose of tool makers microscope?

The tool makers microscope is used to determine many measurements such as Linear measurements, Pitch measurements, thread angle measurements, comparison between standard profile of thread forms, Pitch diameter measurement

The tools makers microscope is based on optical projection method

  1. Explain screw pitch gauge.

Screw pitch gauge is the simplest method of determining the pitch of thread. This type of gauge usually has adjustable anvils which are set the correct distance apart using setting plugs

  1. Mention the different methods of measurement of pitch.

The different methods of measurement of pitch are

  • Pitch measuring machine
  • Tool makers microscope
  • Screw pitch gauge
  1. What is a gear? Mention the types of gear.

Gears are the toothed wheels used for transmission of power or motion from one shaft to another shaft without slip.

Types of Gear

  • Spur gear
  • Helical gear
  • Bevel gear
  1. What is Pitch circle in gears?

In every pairs of gears in mesh, the two circles representing the two plain wheels in contact are always assumed to exist. Each of these circle is called as pitch circle.

  1. Explain addendum and dedendum in gears


Addendum is the radial height of tooth from the pitch circle to the tip of the tooth


Dedendum is the radial depth of tooth from the pitch circle to the root of the tooth

  1. What is Diametral pitch?

Diametral pitch is the number of teeth per unit length of the pitch circle diameter

Diametral Pitch = Number of teeth / Pitch circle diameter = t / d

  1. Define Module.

Module is the linear distance in mm that each tooth of the dear would occupy, if the dear teeth were spaced along the pitch diameter

Module = Pitch circle diameter / Number of teeth = d/T

  1. What are the errors in a gear?

The errors in a gear are

  • Pitch error
  • Profile error
  • Composite error
  • Tooth thickness error
  • Cyclic error
  • Run out
  • Eccentricity
  • Tooth alignment error
  • Periodic error
  1. Mention the elements used to measure a gear

The elements used to gear are

  • Pitch
  • Runout
  • Profile
  • Backlash
  • Lead
  • Tooth thickness
  • Concentricity
  • Alignment
  1. What is Runout?

The eccentricity in the pitch circle is called Runout. This is measured by means of gear eccentricity tester.

  1. What is pitch error?

It is a source of gear noise and the type of noise depend upon how pitch errors are produced. Pitch error is the difference between actual and design pitch

  1. Explain profile error in gears.

Profile error is the maximum distance on the tooth profile form and the normal to the desing when two gears are having contact with each other at reference circle.

  1. What is Optical Projection method?

Optical projection method is one of the methods in profile measurement. In this method, the gear under test is magnified by optical lens and projected on the screen. It is then compared with master profile. This method is quick and suitable for checking the profile of small thin instrument gears.

  1. Explain Constant chord method.

Constant chord method is used for measuring tooth thickness. The constant chord method enables to employ one setting for all the gears having same pitch and pressure angle irrespective of the number of teeth.

  1. What is the purpose of Parkinson gear tester?

Parkinson’s gear tester is a testing device used to measure the variation in the center distance of two gears in mesh. It consists of a master gear and a gear to be tested. Both the gears are rotated, as the gears are rotated the center distance would vary.

Check N Scheme Mechanical Department Study Materials
Strength of Materials Click here
Manufacturing Technology – 1  Click here
Thermal Engineering – 1  Click here
Metrology & Measurements Click here

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