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Engineering Drawings

Engineering Drawings

Detail Drawings. As the product evolves on the layout drawing, the detail of individual components develops. These are documented on detail drawings. Important characteristics of a detail include the following: All dimensions must be toleranced. Most companies have standard tolerances for all but the most critical dimensions. The upper and lower limits of the critical dimensions are given. Materials and manufacturing detail must be in clear and specific language. Special manufacturing processing must be spelled out clearly. Drawing standards such as those given in ANSI Y14.5M-1994, Dimensions and Tolerancing, and in DOD-STD-100, Engineering Drawing Practices, or company standards should be followed. Since the detail drawings are a final representation of the design effort and will be used to communicate the product to manufacturing, each drawing must be approved by management. A signature block is therefore a standard part of a detail drawing. 

Layout Drawings: A layout drawing is a working document that supports thedevelopment of the major components and their relationships.Consider the characteristics of a layout drawing: A layout drawing is a working drawing and as such is frequently changed during the design process. Because these changes are seldom documented, information can be lost. Good records in the design notebook can compensate for this loss. A layout drawing is made to scale. Only the important dimensions are shown on a layout drawing.  Tolerances are usually not shown, unless they are critical. Notes on the layout drawing are used to explain a design feature or the function of the product. A layout drawing often becomes obsolete. As detail drawings and assemblydrawings are developed, the layout drawing becomes less useful. If the product is being developed on a CAD system, however, the layout drawing’s data file becomes the basis for the detail and assembly drawings.

Layout and assembly drawing focus on systems or subsystems, detail drawings address single components.

Assembly Drawings: The goal in an assembly drawing is to show how the components fit together. There are many types of drawing styles that can be usedto show this. Assembly drawings are similar to layout drawings except that theirpurpose, and thus the information highlighted on them, is different. An assemblydrawing has these specific characteristics: Each component is identified with a number or letter keyed to the Bill of Materials (BOM). Some companies put their Bill of Materials on theassembly drawings; others use a separate document. References can be made to other drawings and specific assembly instructions for additional needed information.

Reference: David G. ULLMANThe Mechanical Design Process, 4th edition, Mc Graw Hill, 2010 

Note: The team must include all the relevant Assembly, Sub Assembly, Component and Part drawings as per the Configuration Management Numbering System in the Appendix "E".

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