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LECTURE 06

GeometricDrawing(Machinery)

CBB 1052

ENGINEERING GRAPHICS

Chapter 6

Week 8

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Learning Objectives

By the end of this lecture, student should be

able to :

Create drawing using modify commands

(mirror, rotate, scale, stretch, break, move andcopy )

Distinguish between precise and exact in

geometric drawing

Produce machinery drawing using AUTOCAD

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Other MODIFY tools

3

Please refer toAUTOCAD 2005 Students Manual

Mirror

Rotate

Scale

Stretch

BreakMove

Copy

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Machinery

In industry, the manufacturing of machinery

parts (e.g., screws, fasteners, rivets, nuts

and bolts) and equipment (e.g., gears, shaft,rotating conveyor belts / chains) entails the

needs for precise rather than exact

measurements.

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Tolerancing Dimension

All dimensions should have tolerance due to:

Technology limitationdifficult to manufacture

items (e.g., parts) to their exact size.

Economic feasibilitythe closer to the exact

size, the more expensive the items become.

What is the different between exactand precise?

Tolerancethe amount that a particular dimension is allowed to vary.

- may be expressed through limit dimensioning, plus & minus dimensioning

- is the difference between the max & min limits

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Tolerancing Dimension

High accuracy, but low precision High precision, but low accuracy

-Must have tolerance

-Smaller the tolerance, harder to manufacture but MORE accurate

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Detail drawing of a spur gear

GEARa toothed-wheel mechanical device used to transmit power & motion

between machine parts

Gear Pinion

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Bearingsmechanical devices used to reduce friction & wear between

two parts & to support a load while permitting motion between them.

Characteristics of rolling bearings

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Valvemechanical device to open/close flow in a pipeline

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Drawing: Gears

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Gears (Tooth)

Draw a rectangle(width=1, height=2)

Stretchthe base by 0.5 unit each to the left and right.

The final object (a gears tooth) on the most right.

Grip the base

and then stretch.

A tooth.

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Gears (A Disc + Tooth)

Explodethe

stretched rectangle.

Extendthese two

lines Erasethe base line.

Why do we need a circle with R5.0?

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Gears (Discs + Teeth)

The discs (circles) may be added by usingthe offsetcommand.

Trimthe teeth around the circle with R5.0.

Array (Polar) Angle to fill

= 360

# of items =14

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Gear (final)

Too small to filletimpractical to be exact.

Add tolerance for conformance (customers requirement).

Note:

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