Fundamentals of Dimensioning Rules

(In accordance with ASME Y14.5 - 2018)

1. Each feature shall be toleranced. Tolerances may be applied directly to size dimensions. Tolerances shall be applied using feature control frames when feature definition is basic. Tolerances may also be indicated by a note or located in a supplementary block of the drawing format. See ASME Y14.1 and ASME Y14.1M. Those dimensions specifically identified as reference, maximum, minimum, or stock (commercial stock size) do not require the application of a tolerance.

2. Dimensioning and tolerancing shall be complete so there is full understanding of the characteristics of each feature. Values may be expressed in an engineering drawing or in a CAD product definition data set. See ASME Y14.41. Neither scaling (measuring directly from an engineering drawing graphics sheet) nor assumption of a distance or size is permitted, except in undimensioned drawings, such as loft, printed wiring, templates, and master layouts prepared on stable material, provided the necessary control dimensions are specified. Model data shall be queried when dimensions are not displayed on the model.

3. Each necessary dimension of an end product shall be shown or defined by model data. No more dimensions than those necessary for complete definition shall be given. The use of reference dimensions on a drawing should be minimized.

4. Dimensions shall be selected and arranged to suit the function and mating relationship of a part and shall not be subject to more than one interpretation.

5. The drawing should define a part without specifying manufacturing methods. Thus, only the diameter of a hole is given without indicating whether it is to be drilled, reamed, punched, or made by another operation. However, in those instances where manufacturing, processing, quality assurance, or environmental information is essential to the definition of engineering requirements, the information shall be specified on the drawing or in a document referenced on the drawing.

6. Nonmandatory processing dimensions shall be identified by an appropriate note, such as NONMANDATORY (MFG DATA). Examples of nonmandatory data are processing dimensions that provide for finish allowance, shrink allowance, and other requirements, provided the final dimensions are given on the drawing.

7. Dimensions should be arranged to provide required information for optimum readability.

8. Dimensions in orthographic views should be shown in true profile views and refer to visible outlines. When dimensions are shown in models, the dimensions shall be applied in a manner that shows the true value.

9. Wires, cables, sheets, rods, and other materials manufactured to gage or code numbers shall be specified by linear dimensions indicating the diameter or thickness. Gage or code numbers may be shown in parentheses following the

dimension.

10. An implied 90° angle shall apply where center lines and lines depicting features are shown on orthographic views at right angles and no angle is specified. For information on applicable tolerances for implied 90° angles.

11. An implied 90° basic angle shall apply where center lines of features or surfaces shown at right angles on an orthographic view are located or defined by basic dimensions and no angle is specified. For information on applicable tolerances for implied 90° basic angles.

12. A zero basic dimension shall apply where axes, center planes, or surfaces are shown coincident on ortho-graphic views and geometric tolerances establish the relationship between the features. On CAD models, the distance is basic

when queried model distances are zero and geometric tolerances establish the relationship between the features. For information on applicable tolerances for zero basic dimensions.

13. Unless otherwise specified (UOS), all dimensions and tolerances are applicable at 20°C (68°F) in accordance with ASME B89.6.2. Compensation may be made for measurements made at other temperatures.

14. Unless otherwise specified (UOS), all dimensions and tolerances apply in a free state condition.

15. Unless otherwise specified (UOS), all tolerances and datum features apply for full depth, length, and width of the feature.

16. Dimensions and tolerances apply only at the drawing level where they are specified. A dimension specified for a given feature on one level of drawing (e.g., a detail drawing) is not mandatory for that feature at any other level (e.g., an assembly drawing).

17. Unless otherwise specified (UOS) by a drawing/model note or reference to a separate document, the as-designed dimension value does not establish a functional or manufacturing target.

18. Where a coordinate system is shown on the ortho-graphic views or in the model, it shall be right-handed UOS. Each axis shall be labeled and the positive direction shown.

NOTE: Where a model coordinate system is shown on the drawing, it shall be in compliance with ASME Y14.41.

19. Unless otherwise specified (UOS), elements of a surface include surface texture and flaws (e.g., burrs and scratches). All elements of a surface shall be within the applicable specified tolerance zone boundaries.

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Fundamentals of Dimensioning Rules

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