A hole and shaft combination has a 20H7g6 fit. For 20H7 deviations are 0 & +21 microns and for 20g6 deviations are -7 & -20 micron. Find the maximum clearance between hole and shaft?  

This question was previously asked in
ISRO VSSC Technician-B (Fitter) Official Paper (Held On: 14 July 2021)
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  1. 7 microns
  2. 20 microns
  3. 21 microns
  4. 41 microns

Answer (Detailed Solution Below)

Option 4 : 41 microns
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Detailed Solution

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Concept:

Clearance:

  • In a fit the clearance is the difference between the size of the hole and the size of the shaft which is always positive.

Maximum clearance:

  • In a clearance fit or transition fit, it is the difference between the maximum hole and minimum shaft.

Minimum Clearance:

  • In a clearance fit, it is the difference between the minimum hole and the maximum shaft.

Upper Deviation:

  • It is the algebraic difference between the maximum size and the basic size.

Lower deviation:

  • Lower deviation is the difference between the minimum limit of size and the basic size.

Fundamental deviation:

  • Fundamental deviation is the deviation closest to the basic size.

Calculation:

Given:

Fit: 20H7g6

Hole: 20H7

deviations are 0 & +21 microns

Shaft: 20g6

deviations are -7 & -20 micron

Maximum clearance = (maximum hole) - (minimum shaft)

⇒ Maximum clearance = +21 - (- 20) = +21 + 20 = 41 microns

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