Lecture 16 - AutoCAD 1

Fundamentals of Engineering – Honors – ENGR H191

Question of the Day

Who created the first practical light bulb?

ANSWER: Joseph Swan, an Englishman,

created the first practical light bulb in 1878

Thomas Edison perfected and marketed the design a year later

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Fundamentals of Engineering – Honors – ENGR H191

Dimensioning

GoalsUnderstand the principles of good dimensioning practiceApply the standard dimensioning practices for engineering drawings

ReferenceBTG Chapter 7

– Dimensions and Tolerances

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Fundamentals of Engineering – Honors – ENGR H191

Geometrics

The science of specifying and tolerancing shapes and locations of features of on objects

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Fundamentals of Engineering – Honors – ENGR H191

Geometrics

It is important that all persons reading a drawing interpret it exactly the same way.Parts are dimensioned based on two criteria: Basic size and locations of the features Details of construction for

manufacturingStandards from ANSI (American National Standards Institute)

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Fundamentals of Engineering – Honors – ENGR H191

Scaling vs. Dimensioning

Drawings can be a different scales, but dimensions are ALWAYS at full scale.

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Fundamentals of Engineering – Honors – ENGR H191

Units of Measure

Length English - Inches, unless

otherwise stated Up to 72 inches – feet

and inches over SI – millimeter, mm

Angle degrees, minutes,

seconds

Angle Dimensions

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Fundamentals of Engineering – Honors – ENGR H191

Dimensioning Terminology

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Fundamentals of Engineering – Honors – ENGR H191

(.25 in)

(.375 in)

Dimensioning Standards

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Fundamentals of Engineering – Honors – ENGR H191Dimensioning Basic Shapes -Assumptions

Perpendicularity Assume lines that

appear perpendicular to be 90° unless otherwise noted

Symmetry If a part appears

symmetrical – it is(unless it is dimensioned otherwise)

Holes in the center of a cylindrical object are automatically located

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Fundamentals of Engineering – Honors – ENGR H191

Dimensioning Basic Shapes

Rectangular Prism

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Fundamentals of Engineering – Honors – ENGR H191

Cylinders Positive

Negative

Dimensioning Basic Shapes

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Fundamentals of Engineering – Honors – ENGR H191

Dimensioning Basic Shapes

Cone Frustum

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Fundamentals of Engineering – Honors – ENGR H191

Dimensioning Basic Shapes

Circle Pattern Center Lines

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Fundamentals of Engineering – Honors – ENGR H191

Dimensioning Shows:

Size Location & Orientation

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Fundamentals of Engineering – Honors – ENGR H191

Example Problem

Think Individually, then share with the person next to you.- Compare with the other pair at your table

What dimensions (size & location) are needed?Where should they be placed?

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Fundamentals of Engineering – Honors – ENGR H191

Grouping Dimensions

Yes No

Dimensions should always be placed outside the part

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Fundamentals of Engineering – Honors – ENGR H191

Staggering Dimensions

Put the lesser dimensions closer to the part.Try to reference dimensions from one surface This will depend

on the part and how the tolerances are based.

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Fundamentals of Engineering – Honors – ENGR H191

Extension Line Practices

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Fundamentals of Engineering – Honors – ENGR H191

Repetitive Features

Use the Symbol ‘x’ to Dimension

Repetitive Features

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Fundamentals of Engineering – Honors – ENGR H191Symbols for Drilling Operations

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Fundamentals of Engineering – Honors – ENGR H191

Example Problem

What dimensions (size & location) are needed?Where should they be placed?

Think Individually, then share with the person next to you.- Compare with the other pair at your table

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Fundamentals of Engineering – Honors – ENGR H191

AssignmentsDwg 31 – DIM-1 Fully dimension the objects shown using correct

dimensioning practices.(part is fully dimensioned if it is possible to machine it from the dimensions provided)

Use Inch Dimensions to the second place (x.xx)

Dwg 32 – DIM-2 Fully dimension the objects shown using correct

dimensioning practices. Use one-place metric dimensions (x.x)

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