Dimensioning and Tolerance Symbology, Rules, and Conventions - h1016v2_86
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Figure 5 Example of Dimensioning Notation
Figure 6 Symbology Used in Tolerancing Drawings
Engineering Symbology Prints and Drawings Volume 2 of 2
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DOE-HDBK-1016/2-93
ENGINEERING FABRICATION, CONSTRUCTION,
Engineering Fabrication,
AND ARCHITECTURAL DRAWINGS
Construction, and Architectural Drawings
PR-06
Page 8
Rev. 0
When a drawing is dimensioned, each dimension must have a tolerance. In many cases, the
tolerance is not stated, but is set to an implied standard. An example is the blueprint for a
house. The measurements are not usually given stated tolerances, but it is implied that the
carpenter will build the building to the normal tolerances of his trade (1/8-1/4 inch), and the
design and use of the blueprints allow for this kind of error. Another method of expressing
tolerances on a drawing is to state in the title block, or in a note, a global tolerance for all
measurements on the drawing.
The last method is to state the tolerance for a specified dimension with the measurement. This
method is usually used in conjunction with one of the other two tolerancing methods. This type
of notation is commonly used for a dimension that requires a higher level of accuracy than the
remainder of the drawing. Figure 6 provides several examples of how this type of tolerancing
notation can appear on a drawing.
Tolerances are applied to more than just linear dimensions, such as 1
+
0.1 inches. They can
apply to any dimension, including the radius, the degree of out-of-round, the allowable out-of-
square, the surface condition, or any other parameter that effects the shape and size of the
object. These types of tolerances are called geometric tolerances. Geometric tolerances state
the maximum allowable variation of a form or its position from the perfect
geometry
implied
on the drawing. The term
geometry
refers to various forms, such as a plane, a cylinder, a cone,
a square, or a hexagon. Theoretically these are perfect forms, but because it is impossible to
produce perfect forms, it may be necessary to specify the amount of variation permitted. These
tolerances specify either the diameter or the width of a tolerance zone within which a surface
or the axis of a cylinder or a hole must be if the part is to meet the required accuracy for proper
function and fit. The methods of indicating geometric tolerances by means of geometric
characteristic symbols are shown in Figure 6. Examples of tolerance symbology are shown in
Figure 7.
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