Part Details Review
| Geometric Tolerances |
Geometric tolerancing methods can expand the effective molding tolerance by better defining the size and position requirements for the assembly. Rather than define the position and size of features separately, geometric tolerancing defines a tolerance envelope in which size and position are considered simultaneously.
Figure 1 shows the size and position of a hole specified in both standard and geometric tolerances. The standard tolerances hold the position and size of the hole to 0.003. The geometric tolerances specify a hole-size tolerance of 0.003 but allow the position tolerance to vary within a 0.006 tolerance zone when the hole is at its smallest diameter (maximum material condition). When the hole is larger than the minimum size, the difference between the actual hole size and the minimum hole size can be added to the tolerance zone for the position tolerance. At the maximum hole size, 0.503, the position tolerance zone for the center of the hole is 0.012 or 0.006 from the stated vertical and horizontal positions. As the hole becomes larger, the position can vary more without restricting the required through-hole for the post or screw that passes through the hole (see figure 2).
