Question

A hole shaft pair s designated as $20{\text{H}}_7{\text{f}}_8$ fit.
Given that
$\text{Upper deviation of shaft f" is}-{5.5}^{0.41}$
20 mm falls in the dimension step of 18 mm and 30 mm.
$\text{IT7 = 16 i and IT8 = 25i}$
Use hole based system.

The minimum clearance between the hole and shaft is

• A. 0.074 mm
• B. 0.053 mm
• C. 0.021 mm
• D. 0.020 mm

Answer 1

The correct option is D 0.020 mm

$\text{20 H7 f8}$

$\text{Fundamental deviation}=-5.5{\text{D}}^{0.41}$

$=-0.0199\text{mm}$

$\text{D}=\sqrt{18\times 30}=23.23$

$\text{i}=0.45\times {\text{D}}^{\frac{1}{3}}+0.00\text{D}\text{in}\mu m.$

$=0.0013\text{mm}$

$\text{Tolerance of shaft = IT8 =25i = 0.032 mm}$

$\text{U.L. of shaft = 20 mm - 0.19 mm}$

$=19.98\text{mm}$

$\text{L.L. of shaft = U.L of shaft - tolerances}$

$=19.98-0.032=19.47\text{mm}$

$\text{Minimum clearance}$

$=\text{L.L. of hole - U.L. of shaft}$

$=(20-19.98)\text{mm}=0.02\text{mm}$