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
0.2 Radial eccentricity
Datum axis X
of shoulder of shoulder
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
<t of shoulder
True centre line
<t of shoulder
True centre line
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
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
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
The application of maximum material condition and its relationship with perfect form and squareness
A typical drawing instruction is shown in Fig. 22.22.
T 
0 30.0 
0 0 <M X  
Condition A (Fig. 22.23). Maximum size of feature: zero geometrical tolerance.
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.
