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Dimensional Analysis

Dr. P. M. Pandey

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Types of Dimensions

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Geometry of Form• How flat is flat?

• Is round is perfectly round?

• Is the edge is perfectly straight?• No workpiece is ever produced perfectly. Therefore,

reasonable limits of acceptability are needed so that

deviations can be measured and controlled.• Flatness, roundness, square-ness, concentricity, and

other parameters related to the geometry of form

must be therefore clearly defined and understood bythe process engineer 

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Advantage of using datum for correct

interpretation of geometric tolerances

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Flatness

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Parallelism

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Straightness

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Square-ness or Perpendicularity

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Angularity

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Roundness

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Concentricity and Eccentricity

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Symmetry

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Surface Quality and its Measurement

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Surface roughness measurement

Center-line average value ( Ra) Root-mean-square-average value ( Rq)

Peak to valley height ( R y)

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Three Dimensional Surface Measurement• Optical interference microscopes

• Atomic force microscope

Principle of Contact type surface roughness measuring instruments

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Interpreting Lay

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Interpreting Lay

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Baselines

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Maintaining location of centerlines for better

quality of the part