Chapter 12

Working Drawings

Chapter 12

2Technical Drawing 13th EditionGiesecke, Mitchell, Spencer, Hill Dygdon, Novak, Lockhart

© 2009 Pearson Education, Upper Saddle River, NJ 07458.

All Rights Reserved.

Objectives

• Define top down, bottom up, and middle out design

• Discuss methods of constraining assemblies made using solid modeling and parametric modeling

• Identify the elements of a detail drawing

• List the parts of an assembly drawing




Objectives (cont.)

• List six types of assembly drawings• List the role of the record strip and

title block in the approval process• Describe the process for revising

drawings• Describe the special requirements

of a patent drawing




Top Down Vs. Bottom Up Design• Top down refers to starting the

process of design by:• Considering the function of the entire

system• Breaking it down into subassemblies or

components based on major functions• Each part is manufactured and

assembled




Top Down Vs. Bottom Up Design• Bottom up design is helpful when

the components are standardized parts:• The design process starts at the part

level• Individual components are sized and

designed• Final assembly is built around the

design of the parts




Top Down Vs. Bottom Up Design• Middle out refers to a combination

of top down and bottom up design:• Some parts are standardized• Other parts are designed within the

context of fitting into the design of the assembly




Constraining 3D Assemblies• With constraint based modeling

software, assembly constraints create relationships between modeled parts

• The first part added to the assembly becomes the parent part• Other parts are mated to the parent

part to build up the assembly




Constraining 3D Assemblies




Constraining 3D Assemblies• Subassemblies are groups of

components of a larger machine• Breaking products into

subassemblies can make it easier to coordinate when different designers are working on portions of the same device




3D Layouts and Skeleton Assemblies• An assembly layout or skeleton

assembly can be used to define locations of individual parts in an assembly• Parts are designed so they link to a

skeleton framework in the assembly• The skeleton is a 3D drawing that

defines major relationships in the assembly




Working Drawings or Construction Drawings• Working drawings are a set of

assembly and detail drawing• These drawings are given to

contractors to perform work or manufacture individual parts

• These drawings are legal documents




Assembly Drawings

• Different type of assembly drawings include:• Design assemblies, or layouts• General assemblies• Detail assemblies• Working drawing assemblies• Outline or installation assemblies• Inseparable assemblies (weldments,

etc.)




Assembly Drawings

• Views should show how the parts fit together and suggest function of the unit

• Hidden lines are typically not needed

• Assembly drawings are usually not dimensioned




Detail Drawings

• Detail drawings contain all of the necessary information to manufacture a part

• Detail drawings are also called:• Piece part drawings• Part drawings




Identification




Multidetail Drawings

• When multiple detail drawings are shown on one sheet, identify each part• Place the circles containing the part

numbers adjacent to the parts




Parts Lists

• A parts list or bill of materials (BOM) typically contains:• Part identification number (PIN)• Description of each part• Quantity required in the assembly

• Abbreviations can be used to indicate quantities that are not known such as AR (as required) and EST (estimated quantity)




Parts List




Assembly Sections

• In assembly sections it is necessary to show cut surfaces and distinguish between adjacent parts• To accomplish this, section lines are

drawn in opposing directions• In relatively thin parts, section lines

should be left out or shown solid black• Bolts, nuts, keys, etc. are left

unsectioned




Assembly Sections




Working Drawing Formats

• Number of details per sheet:• Showing one detailed part per sheet

is typically preferred• Machines or structures composed of

few parts sometimes show all the details on one large sheet





• Electronic file formats such as Portable Document Format (PDF) allow the originator to send a document that can be commented on without allowing the original document to be changed

• Using electronic files also saves trees and makes distribution quicker





• Title and record strips show all necessary information not given directly on the drawing with its dimensions and notes

• The type of title used depends on the filing system, manufacturing processes, and requirements of the product





• The title form typically includes:• Name of the object shown• Name and address of manufacturer• Name and address of purchasing

company• Signature of person who made the

drawing and date of completion• Signature of the checker and date of

completion





• Title form information (cont.)• Signature of the chief drafter, chief

engineer, or other official, and the date of approval

• Scale of the drawing• Number of the drawing




Checking Drawings

• The final checker should review the drawing with particular attention to:• Soundness of design• Choice of views• Dimensions• Standard parts• Notes• Clearances• Title form information




Drawing Revisions

• An accurate record of changes made to released drawings is tracked via a revision block

• The record of revisions should show:• What change was made• By whom the change was made• When the change was made• Why the change was made




Simplifying Drawings

• To simplify drawings:• Use word descriptions when practical• Do not show unnecessary views• Use standard symbols and

abbreviations• Avoid elaborate, pictorial, or

repetitive details• List rather than draw standard parts




Simplifying Drawings

• Cont.• Omit unnecessary hidden lines• Use outline section lining in large areas• Omit unnecessary duplication of notes

and lettering• Use symbolic representation for piping

and thread• Use CAD libraries and standard parts

when feasible




Patent Drawings

• Patent applications must include line drawings

• All patent drawings must be mechanically correct and constitute complete illustrations of every feature of the invention claimed

• The U.S. Patent office has strict requirements for patent drawings

Chapter 12

Documents

Transcript of Chapter 12