How do you handle the interaction or interference of projected tolerance zones from different features?

1 Rule 1: Projected tolerance zones are independent

One of the basic rules of geometric dimensioning and tolerancing (GD&T) is that projected tolerance zones are independent from each other, unless otherwise specified. This means that each feature with a projected tolerance zone has its own zone that does not affect or interfere with the zone of another feature. For example, if you have two holes with projected tolerance zones on the same plane, each hole has its own zone that extends from its true profile along its axis, regardless of the position or orientation of the other hole. This allows for more flexibility and variation in the location of the features.

2 Rule 2: Projected tolerance zones can be controlled by datum references

Another rule of GD&T is that projected tolerance zones can be controlled by datum references, which are features that establish a reference frame for the part. Datum references can be used to align, orient, or locate the projected tolerance zones of different features in relation to each other or to the part as a whole. For example, if you have two holes with projected tolerance zones on the same plane, but you want them to be parallel to each other and perpendicular to a datum plane, you can use a datum reference modifier to specify that the projected tolerance zones are controlled by the datum plane. This ensures that the holes are aligned and oriented as intended.

3 Rule 3: Projected tolerance zones can be modified by modifiers

In addition to datum references, projected tolerance zones can also be modified by modifiers, which are symbols that indicate special conditions or requirements for the tolerance zone. Modifiers can be used to limit, expand, or adjust the projected tolerance zones of different features to achieve the desired fit or function of the part. For example, if you have two pins with projected tolerance zones on the same part, but you want them to have a clearance or interference fit with two corresponding holes on another part, you can use a modifier to specify the amount of clearance or interference required. This ensures that the pins and holes have the appropriate fit for assembly.

4 Method 1: Use basic dimensions and coordinate dimensions

One of the methods for dealing with projected tolerance zones from different features is to use basic dimensions and coordinate dimensions. Basic dimensions are dimensions that define the exact size, shape, or location of a feature or a datum reference, and they are shown in a box. Coordinate dimensions are dimensions that define the location of a feature or a datum reference in relation to a coordinate system, and they are shown without a box. By using basic dimensions and coordinate dimensions, you can precisely define the position and orientation of the projected tolerance zones of different features and avoid any ambiguity or confusion.

5 Method 2: Use composite position tolerancing

Another method for dealing with projected tolerance zones from different features is to use composite position tolerancing. Composite position tolerancing is a technique that allows you to control the location of multiple features with projected tolerance zones using two or more tolerance frames. The first tolerance frame, called the pattern locating tolerance frame, controls the location of the entire pattern of features in relation to a datum reference. The second tolerance frame, called the feature relating tolerance frame, controls the location of each individual feature in relation to the pattern locating tolerance frame. By using composite position tolerancing, you can control the interaction or interference of the projected tolerance zones of different features and ensure that they meet the functional requirements of the part.

6 Method 3: Use combined symbols

A third method for dealing with projected tolerance zones from different features is to use combined symbols. Combined symbols are symbols that combine two or more GD&T symbols into one symbol to simplify the drawing and save space. For example, if you have two features with projected tolerance zones that have the same diameter and the same tolerance value, you can use a combined symbol to show both features with one symbol. This reduces the clutter and complexity of the drawing and makes it easier to read and interpret.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?