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An engineered product must have models, drawings, and sketches that document initial design solutions, represent results of analysis, and communicate the final design for production. Production or working drawings are specialized engineering drawings that provide the information required to make the part or assembly of the final design. Working drawings rely on orthographic projection and many other graphical techniques to communicate design information for production.
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BASIC CONCEPTS |
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| 19.1 Engineering drawings are used to communicate designs to others, document design solutions, and communicate design production information. |
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| 19.2-4 Documenting is the process of communicating and archiving design and manufacturing information on a product or structure. The documents created include drawings, models, change orders, memos, and reports. Working drawings are the complete set of standardized drawings specifying the manufacture and assembly of a product based on its design. The complexity of the design determines the number and types of drawings. Working drawings may be on more than one sheet and may contain written instructions called specifications. Working drawings are the blueprints used for manufacturing products. Therefore, the set of drawings must: (a) completely describe the parts, both visually and dimensionally; (b) show the parts in assembly; (c) identify all the parts; and (d) specify standard parts. Generally, a complete set of working drawings for an assembly includes: Detail drawings of each nonstandard part. An assembly or subassembly drawing showing all the standard and nonstandard parts in a single drawing. A bill of materials (BOM). A title block. |
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| 19.5-9 A detail drawing is a dimensioned, multiview drawing of a single part, describing the part’s shape, size, material, and finish, in sufficient detail for the part to be manufactured based on the drawing alone. Standard parts are not drawn as details because they are normally purchased, not manufactured, for the assembly. |
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| 19.10 When more than one detail is placed on a sheet, the spacing between details is carefully planned, including leaving sufficient room for dimensions and notes. |
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| 19.11 An assembly drawing shows how each part of a design is put together. If the design depicted is only part of the total assembly, it is referred to as a subassembly. An assembly drawing normally consists of: All the parts, drawn in their operating position. A parts list or bill of materials (BOM) shows the detail number for each part, the quantity needed for a single assembly the description or name of the part, the catalog number if it is a standard part, and the company part number. Leader lines with balloons, assigning each part a detail number, in sequential order and keyed to the list of parts in the parts list. Machining and assembly operations and critical dimensions related to these functions. |
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| 19.12 Assembly drawings are used to describe how parts are put together as well as the function of the entire unit; therefore, complete shape description is not important. The views chosen should describe the relationships of parts and the number of views chosen should be the minimum necessary to describe the assembly. Dimensions are not shown on assembly drawings unless necessary to provide overall assembly dimensions, or to assist machining operations necessary for assembly. Also, hidden lines are omitted in assembly drawings, except when needed for assembly or clarity. |
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| 19.13 An outline assembly gives a general graphic description of the exterior shape. Outline assemblies are used for parts catalogs and installation manuals or for production when the assembly is simple enough to be visualized without the use of other drawings. |
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| 19.14-15 A sectioned assembly gives a general graphic description of the interior shape by passing a cutting plane through all or part of the assembly. Sectioned assembly drawings are used for the manufacture and assembly of complicated devices. |
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| 19.16 A pictorial assembly gives a general graphic description of each part, and uses center lines to show how the parts are assembled. |
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| 19.17 A 3-D CAD model can also be used to create pictorial assemblies by positioning each part in a pictorial view. |
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| 19.18 Every part in an assembly is assigned a part number, which is usually a string of numbers coded in such a way that a company can keep accurate records of its products. Large aircraft have thousands of parts, and considerable documentation is necessary to design, manufacture, assemble, and maintain the aircraft. Every drawing used in industry is assigned a number. Each company develops its own standard numbering system, based on various criteria such as sequential numbers, combinations of numbers and letters, sheet sizes, number of parts in the assembly, model numbers, function, etc. Both part numbers and drawing numbers are commonly used to name CAD files and code information for company-wide CIM databases. |
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| 19.19 Title blocks are used to record all the important information necessary for the working drawings. The title block is normally located in the lower right corner of the drawing sheet. Title blocks should contain the following: Name and address of the company or design activity. Title of the drawing. Drawing number. Names and dates of the drafters, checker, issue date, contract number, etc. Design approval, when subcontractors are used. Additional approval block. Predominant drawing scale. Federal supply code for manufacturers (FSCM) number. Drawing sheet size letter designation. Actual or estimated weight of the item. Sheet number, if there are multiple sheets in the set. |
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| 19.20 ANSI recommended minimum letter heights for engineering drawings. |
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| 19.21 A complete set of working drawings must include a detailed parts list or bill of material. Based on ANSI standards, a parts list should be located in the lower right corner above the title block. The information normally included in a parts list is as follows: Name of the part. A detail number for the part in the assembly. The part material, such as cast iron or bronze. The number of times that part is used in the assembly. The company-assigned part number. Other information, such as weight, stock size, etc. |
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| 19.22 Information on standard parts, such as threaded fasteners, includes the part name and size or catalog number. |
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| 19.23-24 Parts are identified in assembly drawings by a leader line with an arrow that points to the part. The other end of the leader has a balloon showing the part detail number. |
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| 19.25 Drawing revisions occur because of design changes, tooling changes customer requests, errors, etc. If a drawing is changed, an accurate record of the change must be created and should contain the date, name of the person making the change, description of the change, the change number and approval. This information is placed in a revision block which is normally in the upper right corner of the drawing, with sufficient space reserved for the block to be expanded downward. The scale used on a set of working drawings is placed in the title block. If more than one scale is used, the scale is shown near the detail drawing. Scales are indicated in metric drawings by a colon, such as 1:2; for the English system, an equal sign such as 1=2. |
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| 19.26 The designations METRIC or SI appear in or near the title block to show that metric dimensions and scale are used on the drawing. A graphics scale can also be used, especially on mapping drawings. This graphics scale has calibrations for transferring distances from the drawing to the scale to determine distances. Tolerances are specified in a drawing using toleranced dimensions. For those dimensions that are not specifically toleranced, a general tolerance note is used. |
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| 19.27 The general tolerance note can also contain a general note for angles. |
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| 19.28 Zones are used on large sheets for reference purposes. Zones in engineering drawing are similar to the zones used on highway maps. After a set of working drawings is completed, the set must be thoroughly checked for accuracy. Any changes or errors are commonly marked in red, which is called redlining, and the drawing is sent back to the designer/drafter to make the corrections. |
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| 19.29 Tabular drawings are used when several similar parts have common features. Such parts can be grouped together into a family of parts. |
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| 19.30 A working assembly drawing, also known as a detailed assembly, combines on a single sheet the detail drawing and the assembly drawing, usually a section view. Such drawings are used for relatively simple assemblies that use some standard parts. When a change is needed, a formal request must be made and the stored engineering drawings must be located, retrieved, changed, checked, and approved. The formal request for making a change to existing engineering drawings is called the engineering change order (ECO). Normally, the ECO is accompanied by a copy of the engineering drawing, along with sketches and a written description of the change. A reference number is given to the ECO so that it can be traced within the organization. An engineering change note (ECN) is added to the engineering drawing in the revision block, to document that a change has been made. |
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REPROGRAPHICS |
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Reprographics refers to the technology and techniques of reproducing documents. After the engineering drawings have been created they are copied for others to use, carefully stored, and set up for easy future accessibility. After the original drawing is created, it must be carefully stored or archived. The process used to store and retrieve engineering drawings is called archiving. |
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| 19.31 Blueprinting is a photographic reproduction process in which the copy produced, called a blueprint, has white lines on a blue background. |
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| 19.32 Diazo is a more modern technique similar to the blueprint process The diazo print, also called an ozalid dry print or a blueline print, is a direct-print dry process. Sepias are special prints used as secondary originals. Changes can be made on the sepia, using pencil or ink, and the original can be left unchanged. |
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| 19.33 Xerography is an electrostatic process that transfers images onto ordinary paper. A distinct advantage of the xerographic process is that multiple reduced or enlarged copies can be produced quickly and easily. Engineering drawings produced on large sheets of paper present a significant storage and retrieval problem for industry. One technique for reducing the size of the originals is microfilming, which is a photographic process that produces a small film negative. |
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| 19.34 An aperture card is a long, rectangular card with a rectangular hole for mounting microfilm. |
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| 19.35 Just as CAD has revolutionized the engineering design/drafting process the use of computers for reprographics is revolutionizing the copying storing, and retrieving of engineering drawings. However, a more modern approach would be to use the digital data as the basis for storing, copying, and retrieving the engineering drawings. |
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SUMMARY |
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Working drawings are a fundamental part of any manufacturing or construction business. These drawings document the manufacturing and construction process for simple-to-complex assemblies. Typically, a set of working drawings includes dimensioned detail drawings, assembly drawings, and parts lists normally developed based on ANSI standards. Drawings are numbered according to systems developed within each company, and these numbers form the basis for storage and retrieval of the documents. Traditionally, drawings are created on paper, which must be stored, retrieved, and copied through a process called reprographics. In the future, working drawings may be created, stored, retrieved, and copied using computers alone. |