Geometric characteristic symbols, the tolerance value, modifiers, and datum feature reference letters, where applicable, are combined in a feature control frame to express a geometric tolerance.
- Feature control frame
- Feature control frame incorporating one datum feature reference
- Feature control frame incorporating two or three datum feature references
- Composite feature control frame
- Two single-segment feature control frames
- Combined feature control frame and datum feature symbol
- Feature control frame with a projected Tolerance Zone
Feature control frame
A feature control frame is a rectangle divided into compartments containing the geometric characteristic symbol followed by the tolerance value or description, modifiers, and any applicable datum feature references. See Figs. 3-23, 4-2, and 7-4. Where applicable, the tolerance is preceded by the diameter or spherical diameter symbol and followed by a material condition modifier.
Feature control frame incorporating one datum feature reference
Where a geometric tolerance is related to a datum, this relationship is indicated by entering the datum feature reference letter in a compartment following the tolerance. Where applicable, the datum feature reference letter is followed by a material boundary modifier. See Fig. 3-24. Where a datum is established by two or more datum features (e.g., an axis established by two datum features) all datum feature reference letters, separated by a dash, are entered in a single compartment. Where applicable, each datum feature reference letter is followed by a material boundary modifier. See Figs. 3-25, illustration (a), and 4-25 and para. 4.12.2.
Feature control frame incorporating two or three datum feature references
Where more than one datum is required, the datum feature reference letters (each followed by a material boundary modifier, where applicable) are entered in separate compartments in the desired order of precedence, from left to right. See Fig. 3-25, illustrations (b) and (c). Datum feature reference letters need not be in alphabetical order in the feature control frame.
Composite feature control frame
A composite feature control frame contains a single entry of a geometric characteristic symbol (position or profile) followed by each tolerance and datum requirement, one above the other. See Fig. 3-26, illustration (a), and paras. 7.5.1 and 8.6.
Two single-segment feature control frames
The symbolic means of representing two single-segment feature control frames shall be as shown in Fig. 3-26, illustration (b). Application of this control is described in para. 7.5.2.
Combined feature control frame and datum feature symbol
Where a feature or pattern of features controlled by a geometric tolerance also serves as a datum feature, the feature control frame and datum feature symbol may be combined. The datum feature symbol may be attached to the feature control frame. See Fig. 3-27. In the positional tolerance example in Fig. 3-27, a feature is controlled for position in relation to datums A and B, and identified as datum feature C.
Feature control frame with a projected tolerance zone
Where a positional or an orientation tolerance is specified as a projected tolerance zone, the projected tolerance zone symbol shall be placed in the feature control frame, along with the dimension indicating the minimum height of the tolerance zone. This shall follow the stated tolerance and any modifier. See Figs. 3-28 and 7-21. Where necessary for clarification, the projected tolerance zone shall be indicated with a chain line, and the minimum height of the tolerance zone is specified in a drawing view. The height dimension may then be omitted from the feature control frame. See Fig. 7-22.
Feature control frame placement
A feature control frame is related to a considered feature by one of the following methods and as depicted in Fig. 3-29:
(a) locating the frame below or attached to a leaderdirected note or dimension pertaining to the feature
(b) attaching a leader from the frame pointing to the feature
(c) attaching a side, corner, or an end of the frame to an extension line from the feature, provided it is a plane surface
(d) attaching a side, corner, or an end of the frame to an extension of the dimension line pertaining to a feature of size
(e) placing in a note, chart, or the general tolerance block
Definition of the tolerance zone
Where the specified tolerance value represents the diameter of a cylindrical or spherical zone, the diameter or spherical diameter symbol shall precede the tolerance value. Where the tolerance zone is other than a diameter, the diameter symbol shall be omitted, and the specified tolerance value represents the distance between two parallel straight lines or planes, or the distance between two uniform boundaries, as the specific case may be. In some cases the tolerance zone is nonuniform and is specified as described in para. 8.3.2.
Where the tolerance in a feature control frame is tabulated, a letter representing the tolerance, preceded by the abbreviation TOL, shall be entered as shown in Fig. 3-30.