Metrology UNIT 4

1. UNIT – IV
FORM MEASUREMENT

2. Topics to be covered
1 . Measurement of circularity.
2. Measurement of straightness.
3. Measurement of Flatness.
4. Gear measurement.
5. Surface finish measurement .
6. Screw thread parameter measurements.

3. Errors in Circularity
• Error of circularity is defined as the radial
distance between the minimum circumscribing
circle and maximum inscribing circle.

5. Ovality
Lobing
Different types of Irregularities of a
Circular Part

7. Sources of out-of- roundness
• Clamping distortion, spindle run-out.
• Presence of dirts and chips on clamping
surface.
• Imbalance, heat and vibrations.
• Shafts ground between centers can be out-of-
round due to poor alignment of the centre or
deflection of shafts.
• A round bar or ring-type part held in a 3-or-5-
jaw chuck is compressed at the points of
contact.

8. Measurement of roundness – reference
Circles
1.Least square Circle

9. 2. Minimium Radial separation Circle

10. 3.Maximum Inscribed Circle

11. 4.Minimium Circumscribed Circle

12. Trace produced by a polar recording
Instrument

13. Devices for measurement of Roundness
1. Circumferential confining gauge

14. 2. Rotating on Centres

15. 3.Assessment using V-block

16. Limitations of V-block
1. The angle of V-block very much influence in
the determination of circularity error.
2. Position of the instrument, i.e., whether
measured from top or bottom.
3. Number of lobes on the rotating part.
4. The error of circularity will be influenced by
the radial run out of the part.

17. Major axis 2∆ more
then minor axis
2∆ error revealed when
elliptical object placed
on flat surface

18. Elliptical workpiece tested on V-block of
120 degree

20. Three point probe

21. Roundness measuring spindle-overhead
spindle

23. Roundness measuring spindle-rotating
table

24. Definition of Straightness
• A line is said to be straight over a given length, if
the variation of the distance of its from two planes
perpendicular to each other and parallel to the
general direction of the line remains within the
specified tolerance limits

26. Straight edge
• For checking the straightness of any surface, the
straight edge is placed over the surface and two are
viewed against the light, which clearly indicate the
straightness.
• If the colour of light be red, it indicates a gap of
0.0012 to 0.0017mm.
• If the colour of light be blue, it indicates a gap is
approximately 0.0075mm.

27. Test for straightness by using spirit level
or Autocollimator

30. Cumulative error ; and error w.r.t.
straight edge.

31. Flatness Measurement

33. Flatness Testing

34. Measurement of flatness

35. INTERFERENCE
• Interference is a phenomenon in which
two waves superpose to form a resultant wave of
greater, lower, or the same amplitude.
• Interference usually refers to the interaction of
waves that are correlated or coherent with each
other, either because they come from the same
source or because they have the same or nearly the
same frequency.
• Interferometry is a measurement method using the
phenomenon of interference of waves (usually light,
radio or sound waves)

37. Types of Interference

38. Interferometry

39. Optical Flat

40. Flatness testing by interferometry

41. Test for Convex surface

42. GEARS

43. TYPES OF GEARS

44. A) SPUR GEAR

45. GEAR BOX OF A MOTOR CYCLE
USING SPUR GEARS

46. HELICAL GEARS

47. AUTOMATIC TRANSMISSION OF AN
AUTOMOBILE

48. SPIRAL GEARS

49. BEVEL GEARS

50. DIFFERENTIAL OF AN AUTOMOBILE

51. WORM GEAR

52. WORM GEARBOX OF A CRANE DRIVE

53. Radial drilling machine spindle movement
with rack and pinion arrangement

54. Involute Curve
• An involute curve is defined as the locus of a
point on straight line which rolls around a
circle without slipping.
• G2 R2 = arc GR2

55. Involute Curve

56. Cycloidal Profile

57. Two method of Mfg. Gears
(i) Reproducing method in which the cutting tool
is form cutter, which forms the gear teeth
profiles by reproducing the shape of the cutter
itself. In this method, each tooth space is cut
independently of the other tooth spaces.

59. (ii) Generating method
which the cutting tool (hob) forms the profiles of
several teeth simultaneously during constant
relative motion of the tool and blank.

60. Errors in Mfg. Gears
• The various sources of errors in the gear made
by reproducing method be due to
(i) incorrect profile on the cutting tool,
(ii) incorrect positioning the tool in relation to the
work
(iii) incorrect indexing of the blank.

61. • The sources of error when gears are made by
generating method are :
(i) Errors in the manufacture of the cutting tool
(ii) errors in positioning the tool in relation to the
work.
(iii) errors in the relative motion of the tool and
blank during the generating operation.

62. SPUR GEAR TERMINOLOGY

63. GEAR ERRORS
1.Adjacent Pitch error
2.Cumulative pitch error
3.Profile Error
4.Tooth Thickness Error
5.Runout
6.Radial Run out
7.Axial Run out
8.Backlash

64. Gear Run out:
Total range of reading of a fixed
indicator with the contact points applied to a
surface rotated, without axial movement, about a
fixed axis.
Radial Run out
It is the run out measured along a
perpendicular to the axis of rotation.
Axial Run out
It is the run out measured parallel to
the axis of rotation at a specified distance from the
axis.

65. Backlash
It is defined as the amount by which a tooth space
exceeds the thickness on an engaging tooth.

66. Pitch Measurement

67. Rolling test
• This test reveals any errors in tooth form, pitch
and concentricity of pitch line. When two gears
are in mesh with each other, then any of the
above errors will cause the variation of centre
distance

68. GEAR TESTER

69. PARKINSON GEAR TESTER

70. Tooth Thickness Measurement

71. Constant Chord Method

72. Surface Finish Measurement

73. IMPORTANCE OF SURFACE FINISH
• In order to increase the life of any part which is
subjected to repeated stress, the working and
non-working surfaces must be given very good
surface finish.
• The rate of wear is proportional to the surface
areas in contact and the load per unit area.
• Surface finish also influence the functioning of
machine parts.

74. Reasons for Controlling Surface
Texture
1. To improve the service life of the components
2. To improve the fatigue resistance
3. To reduce initial wear of parts
4. To have a close dimensional tolerance on the
parts
5. To reduce frictional wear
6. To reduce corrosion by minimizing depth of
irregularities
7. For good appearance

75. Factors Affecting Surface Roughness
1. Vibrations
2. Material of the work piece
3. Type of machining.
4. Rigidity of the system consisting of machine
tool, fixture cutting tool and work
5. Type, form, material and sharpness of cutting
tool
6. Cutting conditions i.e., feed, speed and depth
of cut
7. Type of coolant used

76. CLASSIFICATIONS OF GEOMETRICAL
IRREGULARITIES
1.First Order
• Irregularities caused due to lack of straightness of
guide ways on which the tool most moves.
• Surface irregularities arising due to deformation of
work under the action of cutting forces, an due to the
weight of the material itself.
2.Second Order
Irregularities caused due to vibrations.

77. 3.Third order
Due to machining itself (Characteristics of
the process).
4.Fourth order
Arising from the rupture of material
during the separation of the chip.

78. Elements of Surface Texture

79. • The irregularities on the surface of the part
produced can also be grouped into two
categories:
(i) Primary texture (Roughness):
• The surface irregularities of small wavelength
are called primary texture or roughness. These
are caused by direct action of the cutting
elements on the material i.e., cutting tool
shape, tool feed rate or by some other
disturbances such as friction, wear or
corrosion

80. (ii) Secondary texture (Waviness):
The surface irregularities of considerable
wavelength of a periodic character are called
secondary texture or waviness. These irregularities
result due to inaccuracies of slides, wear of guides,
misalignment of centres, non-linear feed motion,
deformation of work under the action of cutting
forces, vibrations of any kind etc.

81. Measurement of surface finish surfaces
texture
1. Surface Inspection of comparison
Methods.
2. Direct instrument measurements.

82. 1. Surface Inspection of comparison
Methods.
(i) Visual Inspection
(ii) Touch Inspection
(iii) Scratch Inspection
(iv) Microscopic Inspection
(v) Surface photographs
(vi) Micro-Interferometer
(vii) Wallace surface Dynamometer
(viii) Reflected Light Intensity.

83. 2. Direct instrument Measurements.
(i)Skid and stylus

85. (ii)Profilometer:

86. (iii)The Taylor Hobson Talysurf

89. (ii) The Tomlinson surface meter

91. Surface Roughness Specification

93. Surface Roughness Symbols

95. Evaluation of Surface Finish

97. 2.The average roughness
(a) C.L.A Method:
(b) R.M.S. Method:
In this method also, the roughness is measured as
the average deviation from the nominal surface.
Root mean square value measured is based on the
least squares.

98. Evaluation of Surface Finish

99. Evaluation of Surface Finish

100. Evaluation of Surface Finish

101. Evaluation of Surface Finish

102. Evaluation of Surface Finish

103. (c) Ten Point Height Method: In this method,
the average difference between the five highest
peaks and five lowest valleys of surface texture
within the sampling length, measured from a
line parallel to the mean line and not crossing
the profile is used to denote the amount of
surface roughness

105. Screw Thread Metrology

106. Bolt Vs Screw

107. Screw Threads
• Screw threads are the most important machine
elements and are used in screws, bolts and
nuts, studs, tapped holes and other power
transmitting devices.
• They are convenient for joining and sealing
purpose.

115. Screw thread terms – External Thread

116. ISO METRIC THREADS

118. TWO WIRE METHOD

119. EXPRESSION FOR BEST WIRE SIZE