Engineering Graphics V

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Engineering Graphics V

• Prof. Jon Southen
• October 20, 2008

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Tolerancing
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Tolerances

• Variations exist in all manufactured parts
• Tolerances specify minimum and maximum allowable
  value of a dimension
• Especially important for systems of with mating
  parts - if tolerances are exceeded, parts may not
  fit together

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Tolerancing

• Allowable variations or tolerances must be
  specified by the designer, with two objectives
• ensure fit and function
• minimize manufacturing cost

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Tolerancing

• Tolerances can drive the manufacturing process
• e.g. a shaft must turn in a hole in a bearing
• hole .7500 to .7512, shaft .7484 to .7492
• function drives tolerance which then drives
  machining process used
• OR
• The manufacturing process can drive the tolerance
• What if drill press is only tool available to
  make the hole, and it can only deliver .748 to
  .754?

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Tolerances of Different Manufacturing Processes
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Tolerance Specific Parts

• If a part is dimensioned 4.650 0.003, it means
  that the part is acceptable within the range
  4.653 and 4.647
• The upper and lower limits are called limit
  dimensions (4.653 and 4.647)
• The tolerance is the difference between the limit
  dimensions ( 4.653 4.647 0.006)

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Tolerance Specific Parts

• Plus and minus tolerance
• e.g. 4.650 0.003 (bilateral tolerance)
• e.g. 4.650 (unilateral tolerance)
• Limit tolerance
• Maximum and minimum sizes are specified directly
• e.g.

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Geometric Dimensioning and Tolerancing (GDT)

• GDT symbols specify additional tolerancing
  information for 3D geometry
• Used in addition to standard /- dimensioning
• Used properly, GDT can allow looser tolerances
  to minimize manufacturing cost

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GDT symbols
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Example
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Working Drawings
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Outline

• Definition of working drawings
• Some basics
• Standard sheet size
• Dimensioning standards
• Drawing scale
• Projection angle
• Title blocks
• Detail drawings
• Assembly drawings
• Examples

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Elements of Engineered Products

• Engineered products contain many parts
• Non-standard parts that must be made
• Standard parts that can be ordered from
  catalogues
• fasteners
• bearings
• gears
• etc.

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Working Drawings

• Working drawings are the complete set of
  standardised drawings specifying the manufacture
  and assembly of a product based on its design.

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Some Basics

• Drawings use standard sheet sizes
• Specified dimensioning standards are used
• Drawings are to a specified scale
• Specified projection angle is used
• First-angle (Europe) or third-angle (North
  America)

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ANSI Standard Sheet Sizes
Metric (mm) U.S. Standard
A4 210 x 297 A-Size 8.5 x 11
A3 297 x 420 B-Size 11 x 17
A2 420 x 594 C-Size 17 x 22
A1 594 x 841 D-Size 22 x 34
A0 841 x 1189 E-Size 34 x 44
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Dimensioning Standards

• Specify appearance of arrowheads, dimension
  lines, text alignment, etc.
• ANSI North America
• ISO Europe
• DIN Germany
• JIS Japan
• Etc.

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Metric Scale

• Each view on a drawing has an associated scale
• Unless otherwise specified, the drawing scale is
  used

11 Full size
12 Half size
15 Fifth size
110 Tenth size
120 Twentieth size
150 Fiftieth size
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Title Blocks

• Drawing title blocks typically contain the
  following
• Name and address of company
• Title of drawing
• Drawing number
• Names and dates of drafter, checker, etc.
• Design approvals
• Predominant drawing scale
• Drawing sheet size
• Weight of item
• Projection angle
• Sheet number (if multiple sheets used)

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Title Block
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Part and Drawing Numbers

• Every part is assigned a unique part number for
  record keeping
• This allows the same part to be used in different
  products
• Every drawing is also assigned a unique number,
  also for record keeping

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Other Required Information

• Revision block
• records revisions to drawing
• CAD packages create these automatically
• Tolerance specifications
• assumed tolerances for all dimensions, unless
  otherwise specified on the drawing

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Requirements for Working Drawings

• Completely describe the parts
• Show the parts in an assembly
• Identify all the parts
• Specify standard parts

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Elements of Working Drawings

• A set of working drawings typically includes
• Detail drawings of each nonstandard part
• Assembly drawings showing all the standard and
  nonstandard parts in a single drawing

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Detail Drawings

• Dimensioned, multi-view drawing of a single part
• All information required for manufacture,
  including
• Dimensions and tolerances
• Material
• Surface finish
• Etc.

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Dimensioned Detail Drawing
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Example Detail Drawing
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http//www.tpub.com/content/draftsman/14040/img/14
040_47_1.jpg
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Assembly Drawings

• Assembly drawings show all the parts and how they
  go together
• Dimensioning is not usually required
• Hidden lines usually omitted
• 3D CAD packages can generate assembly drawings
  directly from assembly models

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Elements of an Assembly Drawing

• All parts shown in one drawing
• assembled view
• sectioned assembly
• exploded assembly
• Parts list or bill of materials (BOM)
• part ID, quantity, description, catalog number,
  etc.
• Balloons
• each part is identified by a numbered balloon,
  and referenced to the parts list
• Machining and assembly instructions

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Assembly Drawing
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Exploded Assembly Drawing
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Sectioned assembly
http//www.jatsgreenpower.com/Uwtech3.gif
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Example
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Example
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Example

• MicroLux Drill Press 81631 Assembly Drawing

http//www.micromark.com/html_pages/instructions/8
1631i/81631g.gif
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Example

• Harley Sportster Transmission

http//www.nightrider.com/biketech/images/xl_cam_a
ssembly.gif
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Example Geared Locomotive (1896)
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Examples from Westerns Formula SAE Team
SolidWorks rendering of 2005 car
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Formula SAE Shock Absorber