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Engineering Metrology (22342) Class – ME3I

Other Measurements

Q. Explain Importance of Surface Finish in engineering applications.

Introduction Functioning of machine parts, load carrying capacity, tool life, fatigue life,
bearing corrosion, and wear qualities of any component of a machine have direct
bearing with its surface texture. Therefore, these effects made the control of surface
texture very important.

The root of any surface irregularity acts as sharp corner and such part fails earlier.

Thus in order to increase the life of any part which is subjected to repeated reversals
of stress, the working and non-working surfaces of that surface must be given very good
finish.

Good bearing properties in any part are obtained when the surface has large number
of irregularities, i.e. a large number of hills and valleys. The rate of wear is proportional
to the surface areas in contact and the load per unit area.

Thus it is seen that different requirements demand different types of surfaces.
Therefore, it became essential to measure the surface texture quantitatively and
methods were devised for this purpose.

The departure from a truly smooth surface may arise from a variety, of causes and
may be of several kinds. The texture or roughness {succession of minute irregularities}
on surface is influenced by the machining process employed.

— Complete roughness is the resultant of irregularities of various kinds.

— If the hills and valleys on a surface are very close, then surface appears as rough.
This is due to action of the cutting tool and is referred to as primary texture.

— If the hills and valleys on a surface are far apart, it is due to imperfection in the
machine tool and is referred to as secondary texture or waviness.

This distinction between primary and secondary texture is due to difference in
wavelength.

A surface actually is quite complex and consists of many different wavelengths
caused due to feed of the tool, cutting action, vibrations, imperfections in machine tools,
etc.

Engineering Metrology (Only For Personal Use) 1