1. Measurement OF SURFACE FINISH
Prof. M. M. Joke
Chapter 7
Measurement OF SURFACE FINISH

2. Prof. M. M. Joke
Introduction
The surface texture greatly influences the functioning of the machined parts.
The properties such as appearance, corrosion resistance, wear resistance, fatigue resistance, lubrication, initial tolerance, ability to hold pressure, load carrying capacity, noise reduction in case of gears,etc. are influenced by the surface texture.

3. Prof. M. M. Joke
Introduction
Whatever may be the manufacturing process used, it is not possible to produce perfectly smooth surface. The imperfections and irregularities are bound to occur.

4. Factors Affecting Surface Roughness
Prof. M. M. Joke
Factors Affecting Surface Roughness
Vibrations.
Material of the workpiece.
Type of machining.
Rigidity of the system consisting of machine tool, fixture, cutting tool and work.
Type, form, material and sharpness of cutting tool.
Cutting conditions i.e. speed, feed and depth of cut.
Type of coolant used.

5. Reasons for controlling Surface Roughness
Prof. M. M. Joke
Reasons for controlling Surface Roughness
It is seen that different requirement demand different surface texture.
Heat exchanger tubes transfer heat better when their surfaces are slightly rough rather than highly finished.
Brake drums and clutch plates, etc. work best with some degree of surface roughness.
The surface of the parts which are subjected to high stresses and load reversals are finished highly smooth.

6. Reasons for controlling Surface Roughness
Prof. M. M. Joke
Reasons for controlling Surface Roughness
The principal reasons for controlling the surface texture are:
To improve the service life of the components.
To improve the fatigue resistance.
To reduce initial wear of parts.
To have a close dimensional tolerance on the parts.
To reduce frictional wear.
To reduce corrosion by minimizing depth of irregularities.
For good appearance.
If the surface is not smooth enough, the moving parts can heat up, blind and freeze.

7. Orders of Geometrical Irregularities
Prof. M. M. Joke
Orders of Geometrical Irregularities
1. First Order: The irregularities caused by inaccuracies in the machine tool itself.
e.g:
i) irregularities caused due to lack of straightness of guideways on which the tool must move.
ii) surface irregularities arising due to deformation of work under the action of cutting forces.
iii) due to weight of the material itself.

8. Orders of Geometrical Irregularities
Prof. M. M. Joke
Orders of Geometrical Irregularities
2. Second Order: The irregularities caused due to vibrations of any kind.
e.g:
i) chatter marks on the surface of the parts.
3. Third Order: The irregularities caused by machining due to characteristic of the process.
i) feed mark of the cutting tool.
4. Fourth Order: The irregularities caused by the rupture of the material during the separation of the chip.

9. Orders of Geometrical Irregularities
Prof. M. M. Joke
Orders of Geometrical Irregularities
The irregularities on the surface of the part produced can also be grouped into two categories:
Primary Texture (Roughness) – Surface irregularities of small wavelength. These are caused by direct action of cutting elements on the material. Includes irregularities of third and fourth order.

10. Orders of Geometrical Irregularities
Prof. M. M. Joke
Orders of Geometrical Irregularities
The irregularities on the surface of the part produced can also be grouped into two categories:
2. Secondary Texture (Waviness) – Surface irregularities of considerable wavelength of a periodic character. These are caused by inaccuracies of slides, wear of guides, misalignment of centres, vibrations, deformation of work, etc. Includes irregularities of first and second order.

11. Orders of Geometrical Irregularities
Prof. M. M. Joke
Orders of Geometrical Irregularities
Primary Texture (Roughness) and Secondary Texture (Waviness)

12. Prof. M. M. Joke
Terminology

13. Sampling Length and Lay
Prof. M. M. Joke
Sampling Length and Lay
Sampling Length – It is the length of the profile necessary for the evaluation of the irregularities to be taken into account. It is also known as ‘cut-off’ length.
It is related to the process employed for finishing.
The standard lengths are 0.08, 0.25, 0.8, 2.5 and 25 mm.

14. Sampling Length and Lay
Prof. M. M. Joke
Sampling Length and Lay
Lay – It is the direction of predominant surface pattern produced by tool marks or scratches. It is determined by the method of production used.

15. Prof. M. M. Joke
Types of Lay

16. Evaluation of Surface Finish
Prof. M. M. Joke
Evaluation of Surface Finish
Three methods of evaluating primary texture (roughness) of a surface:
Peak to valley height method
The average roughness
Form factor or bearing curve

17. Evaluation of Surface Finish
Prof. M. M. Joke
Evaluation of Surface Finish
The Average Roughness – For assessment of average roughness, the following three statistical criteria are used:
C.L.A. Method (Centre Line Average)
R.M.S. Method (Root Mean Square)
Ten point height Method (Rz)

18. Evaluation of Surface Finish
Prof. M. M. Joke
Evaluation of Surface Finish
C.L.A. Method (Centre Line Average)

19. Evaluation of Surface Finish
Prof. M. M. Joke
Evaluation of Surface Finish
C.L.A. Method (Centre Line Average)

20. Evaluation of Surface Finish
Prof. M. M. Joke
Evaluation of Surface Finish
2. R.M.S. Method (Root Mean Square)

21. Evaluation of Surface Finish
Prof. M. M. Joke
Evaluation of Surface Finish
3. Ten Point Height Method (Rz) Rz

22. Statement of Surface Finish
Prof. M. M. Joke
Statement of Surface Finish
Surface Roughness Value – It is expressed as Ra value in microns (μm). If a single Ra value is stated, it is understood that any Ra value from zero to that stated is acceptable.
Limiting Values – When both minimum and maximum Ra values needed to be specified, these shall be expressed as follows:
Ra 8.0/16.0 or alternatively, Ra 8.0 – 16.0

23. Roughness Grade Symbols
Prof. M. M. Joke
Roughness Grade Symbols

24. Symbol to designate Surface finish on drawing
Prof. M. M. Joke
Machining Method
Sampling Length
Roughness value in μm
Machining Allowance
Direction of Lay

25. Symbol to designate Surface finish on drawing
Prof. M. M. Joke
Milling
2.5
6.3 =
1.2

26. Measurement of Surface Finish / Surface Texture
Prof. M. M. Joke
Inspection by comparison (Qualitative Analysis)
Direct Instrument Measurement (Quantitative Analysis)

27. Measurement of Surface Finish / Surface Texture
Prof. M. M. Joke
Inspection by comparison (Qualitative Analysis)
Visual inspection
Touch inspection
Scratch inspection
Microscopic inspection
Surface photographs
Micro-Interferometer
Wallace surface Dynamometer
Reflected light intensity

28. Measurement of Surface Finish / Surface Texture
Prof. M. M. Joke
2. Direct Instrument Measurement (Quantitative Analysis)
Principle : Stylus probe type surface texture measuring instruments – If a finely pointed probe or stylus be moved over the surface of a workpiece, the vertical movement of the stylus caused due to the irregularities in the surface texture can be used to assess the surface finish of the workpiece.

29. Stylus Probe Instruments
Prof. M. M. Joke
Stylus Probe Instruments

30. Stylus Probe Instruments
Prof. M. M. Joke
Stylus Probe Instruments

31. Tomlinson Surface Meter
Prof. M. M. Joke
Tomlinson Surface Meter