Datum feature symbol1/4/2023 ![]() Where it is necessary to control the length of the datum target line, its length and location are dimensioned. Datum Target LinesĪ datum target line is indicated by the datum target point symbol on an edge view of the surface, a phantom line on the direct view, or both. Where there is no direct view, the point location is dimensioned on two adjacent views. Datum Target PointsĪ datum target point is indicated by the target point symbol, dimensionally located in a direct view of the surface. If there is not sufficient space within the compartment, the size and shape of the area may be placed outside and connected to the compartment by a leader line terminating with a dot. Where the datum target is an area, the size and shape of the area (true geometric counterpart) is entered in the upper half of the symbol otherwise, the upper half is left blank. A radial line attached to the symbol is directed to a target point, target line, or target area, as applicable. The lower half contains a letter identifying the associated datum, followed by the target number assigned sequentially starting with 1 for each datum. ![]() The symbolic means of indicating a datum target shall be a circle divided horizontally into halves. (f) placed on a chain line that indicates a partial datum feature. (e) placed above or below and attached to the feature control frame. (d)placed on the horizontal portion of a dimension leader line for the size dimension. For digital data files, the triangle may be tangent to the feature. ![]() (c) placed on the outline of a cylindrical feature surface or an extension line of the feature outline, separated from the size dimension, when the datum is an axis. If there is insufficient space for the two arrows, one of them may be replaced by the datum feature triangle. (b) placed on the dimension line or an extension of the dimension line of a feature of size when the datum is an axis or center plane. On 2D orthographic drawings where the datum feature is not on the visible surface, the leader line may be shown as a dashed line. (a) placed on the outline of a feature surface, on an extension line of the feature outline, clearly separated from the dimension line, when the datum feature is the surface itself, or on a leader line directed to the surface. The datum feature symbol is applied to the feature surface outline, extension line, dimension line, or feature control frame as follows: Where the same datum feature symbol is repeated to identify the same feature in other locations of a drawing, it need not be identified as reference. #Datum feature symbol seriesWhen datum features requiring identification on a drawing are so numerous as to exhaust the single alpha series, the double alpha series (AA through AZ, BA through BZ, etc.) shall be used and enclosed in a rectangular frame. Each datum feature of a part requiring identification shall be assigned a different letter. Letters of the alphabet (except I, O, and Q) shall be used as datum identifying letters. The triangle may be filled or not filled. The symbolic means of indicating a datum feature consists of a capital letter enclosed in a square or rectangular frame and a leader line extending from the frame to the feature, terminating with a triangle. ![]() The symbolic means of indicating geometric characteristics are shown in Fig. In such cases, a note may be used to describe the requirement, either separately or to supplement a geometric symbol. Situations may arise where the desired geometric requirements cannot be completely conveyed by symbology.
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