Routines

List Drawing Signatures, Approvals, Dates

Engineering drawings are among the most valuable of company assets. When drawings are offered into evidence, for instance in patent litigation, an important consideration is the assurance that the document is an authentic record. In this case a signed and properly dated document with the author's handwritten signature has traditionally been an accepted way of authenticating records. This was particularly helpful where the original drawer might no longer be available, and proof of the document origin is now through its current design activity (drawing custodians). However, with most engineering drawings now being CAD-based, computer printed names are the norm rather than original handwritten signatures. Where handwritten signatures are not used, proof of origin is maintained through a chain of design activity documentation. In some cases digital watermarks are being used as are digitized signatures. Revisions are recorded by using a revision authorization document. The starting date can be printed in full or abbreviated. However, it is recommended that the month be shown as two or three alphabetic characters and not as a numerical abbreviation. The reasoning for this is that in a global economy, using a numerical date may cause confusion because of the differences between ISO date formats (dd/mm/yy) and the customary American format which uses (mm/dd/yy). Other approval names and dates may also be shown according to local custom. All names should include initials.

Drawing Numbers By Hyphen, Part & Group

This section describes the numbering of parts and assemblies on drawings. In certain cases it further describes the distinction between part numbers and assembly numbers. It should be noted that the drawing numbering practices described in this section are not based on American National Standards or any other national standards as none currently exist. Nevertheless they do represent common practice in many industries.

Engineering drawings may be:

  1. A single part drawing
  2. A multiple parts drawing
  3. An inseparable assembly (i.e. weldment) drawing
  4. A separate assembly drawing
  5. A layout drawing
  6. An installation drawing
  7. A modifying drawing
  8. A control drawing
  9. An arrangement drawing
  10. A diagram or schematic drawing
  11. A special applications drawing

Casting Practices/Design Considerations

Metalcasting is one of the oldest and most important manufacturing processes today. Basic steps in the metalcasting process consist of making the mold, melting the metal, pouring the liquefied material into the mold, allowing the material to solidify, and removing the solidified casting from the mold. However, to obtain high quality castings with the desired mechanical and physical properties required to meet customer specifications, additional steps are commonly performed.

The main advantages of the metalcasting process include the capability to produce internal cavities with very complex shapes, and to shape hard-to-machine materials. Another important advantage of the casting process is that it is fairly inexpensive when large quantities need to be manufactured. A versatile process, metalcasting can be used to make parts from fractions of an ounce to many tons. Size can be as small as a fraction of a centimeter to over ten meters. With the many different casting processes, designers can easily identify one or several to suit the needs of a particular application.

Specifying Materials, Applied Finishes and Processes

Only a company or National Standard material i.e., SAE, ASME, etc., applied finish and process designation shall be specified on drawings, except:

  1. When military requirements must be met, the appropriate Government or National Standards designation, as applicable, shall be given followed parenthetically by the company equivalent if available. (The equivalent company designation should be equal to or better than the Government or national designation.)
  2. When a material, applied finish or process is specified for which no company designation has been assigned, the chemical composition, physical or electrical properties, or other identifying characteristics, as applicable, shall be given on the drawing.

The material, applied finish or process for a particular item shall be specified only on the drawing on which the part is described and shall not be repeated on any other drawing or parts list.

Associated Lists: Purpose, Classification, and Preparation

Associated lists are part of the overall system of engineering drawings and related documentation. As part of the drawing, or a separate document, lists are meant to convey engineering requirements for parts or products. With the prevailing use of computer-aided design systems (CAD), lists associated with engineering drawings may also be linked to computerized procurement and inventory systems required of a modern manufacturing enterprise. In such an application, typically each row of a list forms a database record while the contents of each column within a row form a database field. Thus this arrangement may be thought of as cells in a spreadsheet.

A list associated with engineering drawings falls into one of six general categories. These include: parts lists, data lists, index lists, application lists, indentured lists and wire lists.

Among the six categories, lists may be one of three types in relationship with engineering drawings. These include:

  1. Integral with the drawing and on the same page as the drawing.
  2. Integral with the drawing but on a separate drawing sheet.
  3. One or more separate sheet forms totally divorced from the drawing sheets.

Reference Documents
American National Standards
    ANSI/ASME Y14.1 - 1995, Decimal Inch Drawing Sheet Size and Format.
    ANSI/ASME Y14.1M - 1995, Metric Drawing Sheet Size.
    ANSI/ASME Y14.2M - 1992, Line Conventions and Lettering.
    ANSI/ASME Y14.34M - 1996, Associated Lists.
    ANSI/ASME Y14.35M - 1997, Revision of Engineering Drawings and Associated Documentation.
    ANSI/IEEE 200 - 1975 (R1989), Reference Desig nations for Electrical and Electronic Parts and Equipment.
U.S. Government Documents
    Cataloging Handbook H4/H8, Commercial and Government Entity (CAGE).

Mechanization Requirements for Engineering Documentation

The word "mechanization" as used in this section refers primarily to a data processing system that permits the orderly compilation, recording and processing of engineering information by machines as opposed to conventional manual methods. Data thus processed are termed outputs that can be identified in two major categories:

  1. required by engineering
  2. required by manufacturing.

To facilitate storage and communication of engineering data in machine-sensible form, and to ensure compatibility with overall systems mechanization, the basic drafting practices described in this section are recommended.

Due to programming or machine limitations, some companies may have found it expedient in the past to incorporate variations of these practices in their mechanized data systems. The up-to-date equipment and programming techniques now available provide these practices. Therefore, where major changes to systems-or complete new systems-are anticipated that include the latest equipment and programming techniques, every effort should be made to update the current systems in accordance with these practices.

Cast, Formed, and Molded Plastic Parts

Drawings for plastic parts are similar to drawings for metallic parts, and dimensioning practices for such drawings are basically universal. The basic difference lies in the proper design of plastic parts with or without inserts, provisions for extracting the parts from the molds, and stress avoidance.

Consistent with casting design, when metallic inserts are imbedded in the plastic part, they should be detailed on a separate drawing, which is called out on the plastic part drawing as a separate dash or suffix number of the plastic detail.

One of the most outstanding and very important characteristics of dimensioning for plastic parts is the judicious use of datums. The use of this characteristic cannot be overemphasized because most plastic parts are produced from molds, which are very costly. To ensure that the plastic parts are produced properly and as economically as possible, datum dimensioning is crucial to their successful production.

Drawing Consideration

In addition to the usual considerations, the following points should be considered when making a detail drawing of a plastic part:

  1. Can the part be removed from the mold?
  2. Is location of flash line consistent with design requirements?
  3. Is section thickness consistent? Thick sections? Thin sections?
  4. Could greater uniformity of section thickness be maintained?
  5. Has the material been correctly specified for the intended application?
  6. Is each feature in accordance with the thinking of competent materials engineers and molders?
  7. Have close tolerance requirements been reviewed with responsible engineers?
  8. Have all requirements been specified?

Design Considerations for Cast, Formed, and Molded Plastic Parts

This section is intended to acquaint the draftsman and engineer with the general characteristics of commercially available plastics, variables that affect the properties of plastics, and the performance of parts made from such materials. The ultimate objective is the proper use of plastics in products. Various manufacturing processes generally used throughout the plastics industry are discussed. Although this information will aid appreciably when designing plastic parts, it should not be permitted to take the place of consultation with the materials application engineer.

Printed Board Drafting Practice

Prior to the actual design layout of a printed board, some important basic elements should be considered by the design engineer or the designer to insure that the printed board is specified correctly to meet the requirements of design, fabrication and assembly. Listed are contributing factors to acquiring a balanced design to meet electrical, mechanical and thermal performance with reliability, manufacturability and board costs considered. The elements listed are general in nature; additional design elements are dependent upon military or commercial requirements, equipment and process applications, and local practices. This checklist approach requires the printed board designer to specify and document the specifics required. This practice also provides documented communications to the design layout function.

Drawing Titles

The titles of items described on drawings shall be brief, descriptive and of uniform definition.

Titles will comprise a basic noun or noun phrase and sufficient modifiers to differentiate like items in the same major assembly. They will be shown on drawings in upper-case letters.

The noun or noun phrase shall establish a basic concept of an item. A compound noun or noun phrase shall be used only when a single noun is not adequate to establish a basic concept of an item.

Gear Drafting Practice

Gears are rotating devices having toothed peripheries which engage one with the other so as to transmit power and/or angular motion between shafts. The shafts may be parallel, or in an angular relationship and their axes may be intersecting or nonintersecting. A rack is a bar having a toothed surface engaging with a gear to convert circular motion to rectilinear motion or vice versa. Gear geometry determines the ratio and constancy of angular velocity, and the smoothness, efficiency and reliability of operation.

In most applications gears must be capable of running without undue noise, vibration, overheating or wear even when thousands of teeth go through mesh in a second's time. Failure to precisely specify certain gear dimensions can result in a worthless product even though all the drawing requirements are met. If the gear manufacturer is obligated to make parts to pass certain running or other functional tests, a simple gear drawing may suffice. If the manufacturer has no obligation except to meet the part drawing, the drawing must clearly show all dimensions, tolerances and process specifications. The principal parts of a gear drawing are as follows:

  1. Axial section through the part.
  2. Tabulation of tooth data.
  3. Cross-section view of tooth.
  4. Isometric view of tooth.
  5. Involute chart.
  6. Plan view of part.
  7. Specifications for material, heat treatments of the material, and accuracy.

Proprietary Information

Recent history and forecasts of the future indicate a continuing increase in the state of technology. Technology is communicated in the form of technical data. This data is a valuable asset of a business. When business relationships evolve between companies (for example, through licensing agreements, joint ventures, off-shore manufacturing, etc.), the protection of technical data through legal agreements and other means becomes vital. An important conduit through which technical data flows is through the engineering drawings prepared by the drafting function. It is through this medium that detailed information is frequently lost to unauthorized sources unless it is appropriately managed, controlled and protected. It behooves management to specifically control the physical location, access to and handling of information of all types. All employees should be carefully instructed as to what information may be disclosed. This section provides guidelines to prevent the loss of technical data.

Reference Documents
  • Defense Acquisition Regulations (DAR) 7-104.9 - Rights in Data and Computer Software.

Forging Practice

Forging is the deforming of a material into a desired design shape via pressure. Forgings are preformed parts of high strength. They have superior resistance to impact loads and other loads because of the grain structure of the material after forming. Forgings are produced usually in forging dies when intricate shapes are required. They can also be produced by hand (smithing) when simple configurations are required, i.e., a round blank, a "doughnut" shape, slab, etc.

Generally the material being forged is worked at an elevated temperature. It is "squeezed" or impacted with a compression force to fill the desired cavity in the die. Some soft materials can be forged without heating. This is referred to as cold forging. Unlike patterns for castings, forging dies are very costly to produce. Therefore, when engineering decisions must be made as to whether a part will be produced as a forging; the production quantity, complexity, load factors, material savings, consistency of quality for the application are among the principal considerations for their use.

Die-Forging Design Considerations

Unlike casting designs which are dependent on material flow by gravity or applied pressure, forging designs depend largely on press capability and die design from which the forging is produced. The intricacies of the casting process cannot be replicated in the forging process. Therefore, forging designs of necessity must be as simple as possible.

Spare- and Repair-Part Kit Drawings

A kit drawing and associated list is a special-purpose document on which are listed parts used to upgrade and maintain an end product. It depicts a packaged unit, item, group of items, instructions, photographs, and other drawings, as required, for modification and/or installation in a product previously supplied to a customer. Normally, the items in a kit do not in themselves constitute a functional assembly.

There are two basic types of kits that are conventionally used; namely, kits that are accumulated or assembled from vendor-supplied parts used in the product, and kits that are put together from parts produced internally by the manufacturer of the product. The latter kit may also include a small portion of vendor-produced items. The basic documentation for these kits is essentially the same. The detail information for the preparation of drawings, lists, and associated data related to these kits is provided in this standard.

Screw-Thread Representations

This document establishes standards for pictorial representation, specification, and dimensioning of unified and metric screw threads on drawings. It is not concerned with standards for the design and dimensional control of screw threads.

Straight unified screw threads are emphasized in this standard in consideration of their widespread use and general-purpose applications. Except for differences noted, the same drafting practices apply to straight pipe threads, tapered pipe threads, helical-coil inserts, and interference threads. Only the more common thread sizes and configurations are covered in this standard.

Screw-Thread Design Considerations

Threaded fasteners and components offer one of the most versatile methods for joining parts and assemblies, especially when disassembly is a design and maintenance consideration. However, their use requires a knowledge of the kinds of threads available for specific applications and the most cost effective methods of manufacture. This section addresses these considerations. The principles and practices covered herein are applicable to both inch and metric threads. It should be noted that the subject of screw threads is highly complex. For this reason, only the highlights are covered in this section. In addition, torque considerations are not covered because this is an individual design factor.

Pipe-Thread Design Considerations

This document provides design standards for the use of pipe threads applied throughout industry. Although most of the detail standards for thread configurations and methods of measurement are a part of the referenced documents, the basic elements are provided in this standard. This document applies to the use of regular pipe threads in any areas of design where pipe threads may be required. Dryseal types of threads used in the automotive, refrigeration, and hydraulics fields are also included.

Reference Documents
    American National Standards Institute, Straight Pipe Threads for Free-fitting Mechanical Joints, Standard B2.1; and Dryseal Pipe Threads, Standard B2.2.

Fastener Selection for Sheet Metal Products and Other Material

Screws are the most commonly used method of fastening or assembling a product, even with the advances in modern adhesive and welding techniques. They are essential to a product's assembly and disassembly for maintenance and service. For a multitude of products, a business's design and manufacturing engineering function normally specifies which screws to select as fasteners. The product designer normally specifies screw size, head style, and length based on application, years of use, and experience. From this experience a fastener standard is normally documented for future product use. There are many types of screws, with thread types, recesses, and head designs for specific applications.

Charts and Graphs

Charts and graphs provide a graphic means for showing data. The presentation of data on a chart or graph gives a visual indication of the relationship between the factors affecting the data. Charts and graphs are often more easily understood than tables containing numbers. For this reason, the data from tables are often converted into charts. It is sometimes necessary to use more than one chart to show all the information in a complex table.

The terms chart and graph are nearly synonymous. Dictionary definitions for the word chart often include the word graph. Graphs are defined as a means for presenting data using either a curve or columns to show the relationship between two or more data items. This indicates that a graph is a type of chart. Any sheet that shows numerical data in graphic form can be labeled a chart. If the graphic form uses either curves or columns to show the data, the chart can be further defined as a graph.

Charts and graphs can be created in many predefined formats using software packages. Some software permits the format to be modified to meet the needs of the user. Manually produced graphs and charts may be produced in any format that clearly presents the data.

Reading a set of graphs and charts can be made easier if the data are presented in a consistent manner. American National Standards previously defined formats for time-series charts and flow diagram symbols, but these standards are no longer active. They have been withdrawn by ASME. However, compliance with the guidelines previously provided by the standards will aid in achieving easy-to-understand charts and graphs. The information contained in this section regarding time-series charts and flow diagram symbols is based on the withdrawn national standards.