Basics of Mechanical Drawing and Dimensioning

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Basics of Mechanical Drawing and Dimensioning ChE 126 Borrowed mostly from the Fundamentals of Engineering Honors program at Ohio State 1

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Basics of Mechanical Drawing and Dimensioning. ChE 126 Borrowed mostly from the Fundamentals of Engineering Honors program at Ohio State. How Would You Describe This?. Describe this using only words How effective is it?. Three Basic Types of Technical Drawings. Freehand sketches - PowerPoint PPT Presentation

Transcript of Basics of Mechanical Drawing and Dimensioning

Page 1: Basics of Mechanical Drawing and Dimensioning

Basics of Mechanical Drawing and Dimensioning

ChE 126

Borrowed mostly from the Fundamentals of Engineering Honors program at Ohio State

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How Would You Describe This?

• Describe this using only words• How effective is it?

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• Freehand sketches

• Instrument drawings

• Computer drawings and models

Three Basic Types of Technical Drawings

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Introduction to Projections

• Present 3-D objects with 2-D media• Two Basic Categories

Orthographic Pictorial

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Orthographic Projection

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Defining the SixPrincipal Views

orOrthographic

Views

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• Hidden Lines – represent features that cannot be seen in the current view

• Centerlines – represent symmetry and mark the center of circles, the axes of cylinders, and the axes of symmetrical parts, such as bolts

Hidden and Center Lines in Orthographic Projections

• Object Lines – represent visible features for an object

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For Example:

1. Visible

2. Hidden3. Center

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Step 1 – Lightly Block Three Views

Use very light lines for drawing in

the construction

lines

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Step 2 – Lightly Block Major Features

Use very light lines for

drawing in the construction

lines

• Holes• Arcs• Cutouts

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Step 3 – Add Final Lines

Use very light lines for drawing in

the construction

lines

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Completed Sketch

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Dimensioning

• Orthographic and isometric views define the shape and general features of the object

• Dimensioning adds information that specifies

– Size of the object

– Location of features (e.g. holes)

– Characteristics of features (e.g. depth and diameter of hole)

• Dimensions also communicate the tolerance (or accuracy) required

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Units of Measure

• Length– English: Inches, unless

otherwise stated• Up to 72"• Feet and inches over 72"

– SI: millimeter, mm

• Angle– degrees, minutes, seconds

Angle Dimensions

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Dimensioning Basic Shapes – Assumptions

• Perpendicularity

• Symmetry

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Dimensioning Basic Shapes

• Rectangular Prism

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Dimensioning Shows:

ALWAYS give DIAMETER " " for full circles (360 degrees) and RADIUS "R" for arcs (less than 360

degrees)

A) Size B) Location and Orientation

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General Guidelines: Clarity is the Goal

• Dimension Outside of View

Avoid Good Practice

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General Dimensioning Guidelines

• Start with basic outside dimensions of the object– Height– Width– Depth

• Add dimension for location and size of removed features

• Add general and specific notes – such as tolerances

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Practice Problem

How many Dimensionsare needed?

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Practice Problem

How many Dimensionsare needed?

Answer: 8