JNTU
JNTU B.Tech III ENGINEERING METROLOGY Previous Question Paper (February - 2022 - R13)
Answer any five questions. All questions carry equal marks.
Main
A clearance fit has to be provided for a shaft and bearing assembly having a diameter of 40 mm. Tolerances on hole and shaft are 0.006 and 0.004 mm, respectively. The tolerances are disposed unilaterally. If an allowance of 0.002 mm is provided, find the limits of size for hole and shaft when (i) hole basis system and (ii) shaft basis system are used.
Answer
Given: Basic size = 40 mm, Hole tolerance (TH) = 0.006 mm, Shaft tolerance (TS) = 0.004 mm, Allowance (A) = 0.002 mm.
(i) Hole Basis System: The basic size is the lower limit of the hole.
Hole limits: Lower limit = 40.000 mm, Upper limit = 40.000 + 0.006 = 40.006 mm.
Shaft limits: Upper limit = Lower limit of hole - Allowance = 40.000 - 0.002 = 39.998 mm. Lower limit = 39.998 - 0.004 = 39.994 mm.
(ii) Shaft Basis System: The basic size is the upper limit of the shaft.
Shaft limits: Upper limit = 40.000 mm, Lower limit = 40.000 - 0.004 = 39.996 mm.
Hole limits: Lower limit = Upper limit of shaft + Allowance = 40.000 + 0.002 = 40.002 mm. Upper limit = 40.002 + 0.006 = 40.008 mm.
Explain why a unilateral tolerance system is generally preferred over bilateral system.
Answer
Unilateral tolerance is preferred because it allows for easier adjustment of the fit without changing the basic size of the part. In this system, the tolerance is applied in one direction from the basic size, which simplifies the manufacturing process and the use of standard gauges. Specifically, if a fit needs to be adjusted, the basic size of the hole remains constant, and only the shaft size is altered, which is more economical in terms of production and inventory management compared to the bilateral system where both limits change relative to the basic size.
List the rules for dimensioning of tolerances and also state the difference between unilateral and bilateral tolerances.
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What is interchangeability? State its need and importance in mass production like Automobile engine components.
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Explain the phenomenon involved in ‘wringing’ of slip gauges.
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Why is a sine bar not suitable for measuring angles above 45 degrees? Discuss in brief.
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Explain why special attention should be given to GO gauges compared to NOT GO gauges during the design of gauges.
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Design GO and NO GO gauges for the hole.
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Explain the measurement methodology involved in the use of optical flats.
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Explain with suitable sketches the measurement of straightness using autocollimator.
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What are interferometers? What are their advantages over optical flats?
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With a neat sketch, explain the measurement of flat surfaces using straight edges.
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Differentiate the primary and secondary texture of surface.
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Explain the different types of irregularities encountered on surfaces. How are the surface contour tests helpful in checking surfaces?
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Explain various terms used for measurement of gear tooth profile. Explain the method for measuring the gear tooth thickness.
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How does a semi-automated CMM differ from a computer-controlled CMM? Also discuss the major applications of CMMs.
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