Machinery's Handbook, 31st Edition
Drawing Checklists 639 If following US practice, are all dimensions, notes and other text readable from the bot tom of the drawing? If following ISO practice, is all dimensional text aligned with each dimension on the drawing? When dimensioning in metric, are preceding 0s shown for values less than 1, and trail ing 0s not shown for integers? (e.g. 0.11 and 10) When heat treatment is required, the heat treatment should be specified. When dimension in inches, are preceding 0s not shown for values less than 1, and trail ing 0s added for consistent significant digits? (e.g. 11 and 10.00) If dimensioning symbols are used, such as depth, diameter, radius, etc., are the symbols placed before the dimensional value? Are quantities specified for all dimensions or features occurring in multiple locations (via 2X or TWO TIMES)? Are threaded holes specified by tap drill and thread specifications to avoid potential look-up errors? Are all occurrences of dimensional and non-dimensional text to consistent size or per company policy? Are dimensions to hidden lines and those directly to object lines minimized unless impossible to avoid? Are dimensions shown in a view depicting the true shape projection of the feature? Do all dimensions account for tolerance, either directly or indirectly, via note or block tolerance? Does the selection of paper size match the complexity of the part to avoid over-crowding via a size too small or wasted space via a size too large? Are dimensions shown in a form that minimizes unnecessary calculations by readers of the drawing? Are views aligned left-to-right and bottom-to-top, and arranged properly for 3rd angle projection (or 1st angle projection)? Is the primary view the most descriptive view possible? Is chain dimensioning minimized to avoid “stacking” of tolerances? Are holes and other round features and parts located by their centers? Are witness lines (extension lines) used with dimensions rather than dimensioning directly to features? Is the drawing title correct and the drawing number or file name in the correct format? Arrangement of Views.— A drawing may show one or more views of an object arranged according to a definite plan. In the United States, the general practice is to place the top view above the front view, and the end view next to whatever end it represents. For exam ple, if a view of the left-hand end is considered important, the end view is placed to the left of the front view. If a right-hand view is also necessary, it is placed to the right of the front view. If a bottom view is needed, it is placed below the front view. The view obtained by looking at an object from above is a plan view. The view obtained by looking at the object from its side and showing a vertical face is an elevation, which may be either a front elevation or an end elevation (also known as side elevation). Third-angle and First-angle Projection: If the views are placed with the plan above the front elevation, the right-hand end view to the right and the left-hand end view (when drawn) to the left, this is known as third-angle projection . In ISO practice, it is the custom to use what is known as first-angle projection . With this method, the front elevation is placed at the top, the plan view at the bottom, the right-hand end view at the left, and the left-hand end view at the right. The first-angle projection is also generally employed in architectural and structural work, as in drawings of bridges, etc. See Fig. 1a and Fig. 1b on page 626.
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