9. Geometric Features.pdf

# A circle is drawn around all the data and is shrunk

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A circle is drawn around all the data and is shrunk until it is constrained by three peaks The roundness error is simply the largest valley measured from this circle This method is also unique but it suffers from the fact that the centre position is determined by only three points. A large stray peak can produce an erroneous centre position, which can invalidate eccentricity and concentricity measurements.

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30 Max. Inscribed Circle (MIC) MI Circle Roundness error Corresponds to plug gauge This is the opposite of the MCC. A circle is drawn within all the data and is expanded until it is constrained by three valleys. The roundness error is simply the largest peak measured from this circle. Unfortunately the centre obtained by this method need not be unique. E.g. dumbbell.
ISO/R 1101-1983 recommends a minimum zone evaluation of form and specifies that an ideal/reference feature must be established from the actual measurement data such that the deviation between ideal feature and the actual feature concerned will be the least possible value. But no methods of fitting have been recommended ISO Definition ISO, Geneva, ISO 1101-1983 , Technical drawings: Tolerancing of form, orientation, location, and runout - Generalities, definitions, symbols, indications on drawing.

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32 Minimum Zone Circles (MZC) Roundness error Two concentric circles; one outside and the other inside the actual profile are established such that their radial separation is the least. This method has some ambiguity brought about by the inner circle in the same way as plug gauge but it is not usually considered to be a severe problem. The actual zone is not ambiguous. It is simply the smallest in value. This smallest zone is the roundness error.
33 GATE 1998 Autocollimator is used to check (a) roughness (b) flatness (c) angle (d) automobile balance Ans.: b

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34 GATE 1997 Match the following List I List II (A) Surface profilometer (1) Calibration (B) Light Section Microscope (2) Form tester (C) Microkater (3) Film thickness measurement (D) Interferometer (4) Centre line average (5) Comparator (6) Surface by measurement Ans.: A – 2 B – 3 C – 5 D – 1
35 GATE 1995 Match the following List I List II (A) Talysurf (1) T-Slots (B) Telescopic gauge (2) Flatness (C) Transfer calipers (3) Internal diameter (D) Autocollimator (4) Roughness Ans.: A – 4 B – 3 C – 1 D – 2
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• Geometry, Euclidean geometry, Line segment

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