Maximum material condition and perfect form

When any errors of geometrical form are required to be contained within the maximum material limits of size, it is assumed that the part will be perfect in form at the upper limit of size.

In applying this principle, two conditions are possible.

Case 1 The value of the geometrical tolerance can progressively increase provided that the assembly diameter does not increase above the maximum material limit of size. Figure 22.17 shows a shaft and the boxed dimension, and indicates that at maximum material limit of size the shaft is required to be perfectly straight.

0.2 Radial eccentricity

Datum axis X

0.2 Radial eccentricity

Datum axis X

Eccentricity Dimensioning

of shoulder of shoulder

Fig. 22.15

Condition C (Fig. 22.16). Shows the situation where the smallest size shoulder is associated with the datum shaft at its low limit of size. Here the total coaxiality tolerance which may be permitted is the sum of the specified coaxiality tolerance + limit of size tolerance for the shoulder + tolerance on the shaft = 0.2 + 0.2 + 0.02 = 0.42 diameter.

0.2 Radial eccentricity

0.01 Radial eccentricity

0.2 Radial eccentricity

0.01 Radial eccentricity

Pin Eccentricity Examples

<t of shoulder

True centre line

<t of shoulder

True centre line

Fig. 22.17

Figure 22.18 shows the shaft manufactured to its lower limit of size, where the permitted error in straightness can be 0.05, since the assembly diameter will be maintained at 16.00. Similarly, a shaft manufactured to, say, 15.97 can have a permitted straightness error of 0.03.

Cylindrical tolerance zone 0 0.05

0 15.95

0 15.95

cL of part

Fig. 22.18

Case 2 The geometrical tolerance can also be limited to a certain amount where it would be undesirable for the part to be used in service too much out of line.

Figure 22.19 shows a shaft, with a tolerance frame indication that at the maximum material limit of size the shaft is required to be perfectly straight. Also, the upper part of the box indicates that a maximum geometrical tolerance error of 0.02 can exist, provided that for assembly purposes the assembly diameter does not exceed 14.00.

0 0.02

0 0 M

Figure 22.20 shows the largest diameter shaft acceptable, assuming that it has the full geometrical error of 0.02. Note that a shaft finished at 13.99 would be permitted a maximum straightness error of only 0.01 to conform with the drawing specification.

— Effective assy dia

Figure 22.20 shows the largest diameter shaft acceptable, assuming that it has the full geometrical error of 0.02. Note that a shaft finished at 13.99 would be permitted a maximum straightness error of only 0.01 to conform with the drawing specification.

— Effective assy dia

Straightness Gauge For Shanks

Fig. 22.20

Figure 22.21 shows the smallest diameter shaft acceptable, and the effect of the full geometrical error of straightness.

Effective assy dia

Effective assy dia

Fig. 22.21

The application of maximum material condition and its relationship with perfect form and squareness

A typical drawing instruction is shown in Fig. 22.22.

30.6

T

0 30.0

0 0 <M X

Condition A (Fig. 22.23). Maximum size of feature: zero geometrical tolerance.

0 30.6

Datum face X

1

f-

-1

Condition B (Fig. 22.24). Minimum size of feature; Permitted geometrical error = 0.6.

Note that between these extremes the geometrical tolerance will progressively increase; i.e. when the shaft diameter is 30.3, then the cylindrical tolerance error permitted will be 0.3.

Fig. 22.24

The application of maximum material condition and its relationship with perfect form and coaxiality

A typical drawing instruction is shown in Fig. 22.25.

0 0 M

15.0 „0 14.9 „

Condition A (Fig. 22.26). Head and shank at maximum material condition. No geometrical error is permitted, and the two parts of the component are coaxial.

5

Condition B (Fig. 22.27). Head at maximum material condition; shank at minimum material condition. The permitted geometrical error is equal to the tolerance on the shank size. This gives a tolerance zone of 0.1 diameter.

— Cylindrical tolerance zone 0.05 radius over shank length

Fig. 22.27

Condition C (Fig. 22.28). Shank at maximum material condition; head at minimum material condition. The permitted geometrical error is equal to the tolerance on the head size. This gives a tolerance zone of 0.1 diameter.

Cylindrical tolerance zone 0.05 radius over head length

Fig. 22.28

Condition D (Fig. 22.29). Both shank and shaft are finished at their low limits of size; hence the permitted geometrical error will be the sum of the two manufacturing tolerances, namely 0.2 diameter.

The application of maximum material condition to two mating components

Figure 22.30 shows a male and female component dimensioned with a linear tolerance between centres, and which will assemble together under the most adverse conditions allowed by the specified tolerances. The male component has centre distance and diameters of pins at maximum condition. The female component has centre distance and diameter of holes at minimum condition.

60 ± 0.1

+G.1 2 holes 0 15.G

r/j

V/////A

V\

6G ± G.1

The tolerance diagram, Fig. 22.31, shows that, when the pin diameters are at the least material condition, their centre distance may vary between 74.9 - 14.7 = 60.2, or 45.1 + 14.7 = 59.8. Now this increase in tolerance can be used to advantage, and can be obtained by applying the maximum material concept to the drawing detail.

60.2 max effective centres

Cylindrical tolerance zone G.G5 radial over head length

Cylindrical tolerance zone G.G5 radial over shank length

(H of shank

60.2 max effective centres

Maximum Material Principle

Similarly, by applying the same principle to the female component, a corresponding advantage is obtainable. The lower part of Fig. 22.31 shows the female component in its maximum material condition. Assembly with the male component will be possible if the dimension over the pins does not exceed 74.9 and the dimension between the pins is no less than 45.1.

Figure 22.32 shows the method of dimensioning the female component with holes controlled by a positional tolerance, and modified by maximum material condition. This ensures assembly with the male component, whose pins are manufactured regardless of feature size.

When the maximum condition is applied to these features, any errors of form or position can be checked by using suitable gauges.

15.1

2 holes 0 15.0

15.1

2 holes 0 15.0

Hole Geometric Position

Fig. 22.32

For further details regarding maximum and minimum condition refer to BS EN ISO 2692.

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Responses

  • tiblets
    What is Maximum material in drawing?
    8 years ago
  • tolomeo
    How to be perfect in engineering drawing?
    8 years ago
  • ross
    What is eccentricity in engineering drawing and tolerance?
    8 years ago
  • Rita Morton
    When zero mzximum material condition?
    8 years ago

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