9. Geometric Features.pdf

# ² color of the light which is due to interference

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² Color of the light, which is due to interference caused by diffraction, is observed ² Red – 1.2 to 1.8 µ m ² Blue – 8 µ m approx. ² This method is suitable for lapped surfaces . Granite Straight Edge

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v Suitable for coarser work v Straight edge is supported between two points with minimum deflection ( 0.554 l ) using two unequal piles of slip gauges thus creating the wedge as shown in Fig. v Let the separation distance between the supports be 200 mm. v Each of 0.01 mm height variation corresponds to a displacement of 20 mm. 0.554 l l Contact position Nominal position Error = 0.004 mm 10 10.1 10.05 8 mm Testing straightness using wedge method Wedge Method Straight edge
10 Autocollimator Photographic view of autocollimator

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11 What is an autocollimator? ² An optical instrument that is used to measure small angles with very high sensitivity. ² Provides non-contact measurement. Reflection from a plane surface turned through angle δ θ Reflections from a plane surface Principles of operation
12 Straightness checking – Auto-collimator and reflector Auto-collimator Method

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13 Conversion of angular deviation into a linear deviation 180 0 = π radians 1 deg.of arc = π 180 radians 60 min. of arc = π 180 radians 1 min. of arc = π 180x60 radians 1secof arc = π 180x60x60 radians 0.005x10 3 radians Ona baselengthof 100mm, 1 secof arc = 0.005x10 3 x100 = 0.5x10 3 mm or0.5 μ m
14 Observations Position on Surface Reading Avg. Reading min sec Difference from 1 st Reading (sec) Rise or Fall in Interval length ( μ m) Cumulative values ( μ m) Adjustment to bring both ends to Zero ( μ m) Deviations from Straight line ( μ m) Forward min sec Backward min sec 0 2 8 2 12 1 2 8 2 12 2 2 11 2 15 3 2 15 2 19 4 2 8 2 8 5 2 9 2 11 6 2 14 2 14

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15 Straightness error = | d max | + | d min | = |+2| + |-1| = 3 μ m Straightness Evaluation Position on Surface Reading Avg. Reading min sec Difference with 1 st Reading (sec) Rise or Fall in Interval length ( μ m) Cumulative values ( μ m) Adjustment to bring both ends to Zero ( μ m) Deviations from Straight line ( μ m) Forward min sec Backward min sec 0 2 8 2 12 2 10 0 0 0 0 0 1 2 8 2 12 2 10 0 0 0 -1 -1 2 2 11 2 15 2 13 +3 +1.5 +1.5 -2 -0.5 3 2 15 2 19 2 17 +7 +3.5 +5 -3 +2 4 2 8 2 8 2 8 -2 -1 +4 -4 0 5 2 9 2 11 2 10 0 0 +4 -5 -1 6 2 14 2 14 2 14 +4 +2 +6 -6 0
16 Cumulative and Actual Error Graphs 0 1 2 3 4 5 6 7 1 2 3 4 5 6 7 Cumulative error (microns) Position on surface Cumulative Graph Actual Error Graph -1.5 -1 -0.5 0 0.5 1 1.5 2 2.5 1 2 3 4 5 6 7 Position on surface Error from straight line (microns)

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Roundness or Circularity If you desire to blossom like a rose in the garden, you have to learn the art of adjusting with the thorns.” ~ Anonymous
18 Roundness
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• Winter '15
• Subbu
• Geometry, Euclidean geometry, Line segment

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