The document provides an overview of surface finish measurement in mechanical measurement and metrology, detailing various classifications of surface texture and terminology. It outlines several methods for measuring surface finish, including comparison, direct instrument measurement, and other techniques, while highlighting the importance of surface finish on fatigue strength, wear resistance, and corrosion resistance. Several instruments and methods, such as profilometers and optical measurement techniques, are described for assessing surface characteristics.

1. Mechanical
measurement and
Metrology
Surface finish measurement
Prepared by – Navroz
Navodia

2. Surface texture
• The characteristic quality of an actual surface due to
small departures from its general geometrical form a
pattern or texture on the surface
• The problem is basically geometrical
• They are classified as follows
1. First order – due to inaccuracy of machine tool
2. Second order-due to vibration of any kind
3. Third order-due to characteristic property of machine
4. Fourth order-due to rupture of material

3. Surface finish terminology
1. Roughness
2. Waviness
3. Surface
4. Actual surface
5. Nominal surface
6. Roughness height
7. Roughness width
8. Roughness width cut-off
9. Waviness height
10.Waviness height
11.Profile
12.Centre line
13.Effective profile

4. Methods of measuring surface
finish
1. Surface inspection by comparison method
2. Direct instrument measurement
3. Other methods of measuring surface finish

5. Comparison methods
1. Touch inspection:
• In this method finger tip is moved at a speed of
25mm per second and irregularities upto 0.01mm
can be measured.
2. Visual inspection:
• Means visualizing by naked eyes and is just a
subjective evaluation.

6. Comparison methods
3. Scratch inspection
• Lead or babbit or plastic is moved along the surface to
be inspected.
4. Microscopic inspection
• Microscope can only measure small surface.
• Compared with a master surface.
• 5. Surface photograph
• Magnified photograph with different illumination are
taken.

7. Comparison methods
6. Micro interferometer
• In this method an optical face is placed on the surface
to be inspected and illuminated by a monochromatic
light and then interference band are studied by
microscope.
7. Wallace dynamometer
• It consists of a pendulum which is lifted to initial
position and allowed to swing over testing surface.
Surface smoothness is determined by friction as swing
time is a direct measure of surface finish.

8. Comparison methods
8. Reflected light intensity
• In this method a beam of light(known qty.) is
projected upon surface and is reflected in several
directions as beams of lesser intensity and change in
length in different directions is measured by photocell.

9. Direct instrument measuring
method
1. Profilometer
• Commonly used in
U.S.A. for direct
measurement of
surface quality
• This instrument is best
suited for measuring
surface finish of deep
bores.

10. Direct instrument measuring
method
2. Tomlinson Surface Tester
• Design by Dr. Tomlinson.
• It is reliable and cheaper.
• It is slow in operation.
• Not suitable for continuous use.
• Delicate and requires great care.

11. Direct instrument measuring
method

12. Direct instrument measuring
method
3. The Taylor-Hobson Talysurf
• The Talysurf is an electronic instrument working on
carrier modulating principle.
• Microprocessors have made available complete
statistical multi-trace systems measuring several
places over a given area and can provide standard
deviations and average over area-type readings and
define complete surface characterisation.

13. Direct instrument measuring
method

14. Direct instrument measuring
method
4. Profilograph

15. Direct instrument measuring
method
5. Light cross section method

16. Other methods for measuring
surface roughness
• 1. Pneumatic method
• Also known as air
leakage method
• Pneumatic comparator
is used
• Air discharge is
measured by a special
variable air flow meter

17. Other methods for measuring
surface roughness
2 Light interference
microscope
• It is a non contact
process
• It is directly related to
RA value
• Good resolution can
give scratch spacing of
0.5 micrometer.

18. Mecrin instrument
• This instrument
assesses the surface
through its frictional
property and the
average slope of the
irregularities
• Ra values ranges from
3-5 micrometer

19. Adverse effect of poor surface
finish
1. Fatigue strength
• High surface finish increase fatigue strength
2. Wear resistance
• Decreases with poor surface finish
3. Corrosion resistance
• Decreases with poor surface finish

20. Thank you