Engineering Graphics V Prof. Jon Southen October 20, 2008

Tolerancing

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

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

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?

Tolerances of Different Manufacturing Processes

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)

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.

Geometric Dimensioning and Tolerancing (GD&T) GD&T symbols specify additional tolerancing information for 3D geometry Used in addition to standard +/- dimensioning Used properly, GD&T can allow looser tolerances to minimize manufacturing cost

GD&T symbols

Example

Working Drawings

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

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.

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

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)

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” ANSI Standard Sheet Sizes

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

Metric Scale Each view on a drawing has an associated scale Unless otherwise specified, the drawing scale is used 1:1 Full size 1:2 Half size 1:5 Fifth size 1:10 Tenth size 1:20 Twentieth size 1:50 Fiftieth size

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)

Title Block

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

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

Requirements for Working Drawings Completely describe the parts Show the parts in an assembly Identify all the parts Specify standard parts

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

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

Dimensioned Detail Drawing

Example Detail Drawing

http://www.tpub.com/content/draftsman/14040/img/14040_47_1.jpg

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

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

Assembly Drawing

Exploded Assembly Drawing

Sectioned assembly http://www.jatsgreenpower.com/Uwtech3.gif

Example

Example

Example MicroLux Drill Press #81631 Assembly Drawing http://www.micromark.com/html_pages/instructions/81631i/81631g.gif

Example Harley Sportster Transmission http://www.nightrider.com/biketech/images/xl_cam_assembly.gif

Example: Geared Locomotive (1896)

Examples from Western’s Formula SAE Team SolidWorks rendering of 2005 car

Formula SAE Shock Absorber