Perspective Represntation

DIMENSIONING WORKIN G DRAWINGS Footer Text 02/25/20 1

Dimensioning Line Types extension lines: "extends" from the object with a gap of about 1 mm from the object, and continues to about 3mm past the last dimension line. dimension lines:

lines with arrowheads carrying the dimension digits. arrowheads can be represented three different ways; arrowhead, slash, or dot. 02/25/20 2

Dimensioning Line Types centre lines and reference lines: alternating long and short dashes which indicates the centre or reference for a particular feature. these lines may be used as extension lines for dimensioning. leaders:

thin uniform curved lines ending with arrowheads pointing to the feature to which they refer. 02/25/20 3 Dimensioning Line

Types Notes: In order to completely describe an object, notes are sometimes given on the drawings (e.g., All rounds and fillets 2 mm radius). These notes are usually located on the right column of the drawing above the title block.

02/25/20 4 Dimensioning Symbols Standard Engineering practices allow for symbols to be used to simplify the drawing. The following are examples of such symbols:

DIA. O RADIUS R 02/25/20 5

Methods of Dimensioning Aligned: all dimension figures, except those that apply to angular contours should be lettered parallel to the dimension lines. Unidirectional: all dimensions figures should be lettered parallel to the bottom edge of the paper.

02/25/20 6 Types of Dimensioning Overall Dimensions: indicates the overall length, width or height of the object.

Detail Dimensions: provides information about size or location of any feature or detail about the part. 02/25/20 7

Dimensioning Rules A technical drawing must always specify the full-size dimensions of an object regardless of the scale to which the drawing has been prepared. The units of measurement on metric technical drawings are assumed to be millimetres unless otherwise specified.

02/25/20 8 Basic Dimensioning Rules Extension lines are solid continuous lines. Leave a visible gap between the feature and the extension line Extension lines should extend just beyond the

dimension line Review Basic Dimensioning Rules Place dimensions off, between, or above the views. when possible

Basic Dimensioning Rules Dimension a feature where its shape is best shown. Basic Dimensioning Rules Dimension a feature only once; no duplicate dimensions Basic Dimensioning Rules

Omit one detail dimension in a chain. Basic Dimensioning Rules Dimension to object lines; avoid dimensioning hidden lines Basic Dimensioning Rules Place consecutive detail dimensions in line

Basic Dimensioning Rules Dimension the object rather than the space Basic Dimensioning Rules Extension lines begin about 2mm from the feature being dimensioned.

Correct Incorre ct Basic Dimensioning Rules Dimension obviously identical features only once

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