Machine Drawing

222 Machine Drawing

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d:\N-Design\Des15-1.pm5

For each letter symbol from a to zc for shafts and A to ZC for holes; the magnitude and

size of one of the two deviations may be obtained from Table 15.2 or 15.3 and the other deviation

is calculated from the following relationship :

Shafts, ei = es – IT

Holes, EI = ES – IT

where IT is fundamental tolerance of grade obtained from Table 15.1.

NOTE The term ‘shaft’ in this chapter includes all external features (both cylindrical

and non-cylindrical) and the term ‘hole’ includes all internal features of any component.

15.3.2.1 Formulae for calculating fundamental shaft deviations

Table 15.4 shows the formulae for calculating the fundamental deviation of shafts. The value

of D is the geometric mean diameter of the range.

Table 15.4 Formulae for fundamental deviation for shafts upto 500 mm

Upper deviation (es) Lower deviation (ei)

Shaft In microns Shaft In microns

designation (for D in mm) designation (For D in mm)

a = – (265 + 1.3D) k4 to k7 = 0.6^3 D

for D ≤ 120

= – 3.5 D k for = 0

for D > 120 grades ≤ 3

and ≥ 8

b ≈ – (140 + 0.85 D) m = + (IT 7 – IT 6)

for D ≤ 160

≈ – 1.8 D n = + 5 D0.34

for D > 160 p = + IT 7 + 0 to 5

c = – 52 D0.2 r = geometric mean of values

for D ≤ 40 ei for p and s

= – (95 + 0.8 D) s = + IT 8 + 1 to 4

for D > 40 for D ≤ 50

d = – 16 D0.44 = + IT 7 + 0.4 D

for D > 50

e = – 11 D0.41 t = IT 7 + 0.63 D

f = – 5.5 D0.41 u = + IT 7 + D

g = – 2.5 D0.34 v = + IT 7 + 1.25 D

h = 0 x = + IT 7 + 1.6 D

y = + IT 7 + 2 D

z = + IT 7 + 2.5 D

za = + IT 8 + 3.15 D

zb = + IT 9 + 4 D

j5 to j8 no formula zc = + IT 10 + 5 D

For Js : the two deviations are equal to ±

IT

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