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ENGR 114 Chapter 2: Scale and Projections

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## ENGR 114 Chapter 2: Scale and Projections

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**1. **ENGR 114 Chapter 2: Scale and Projections

**2. **Scale Scales are used to measure distances on technical drawings.
Types of scales
Mechanical Engineers Scale (Fractional divisions)
Civil Engineer’s Scale (Division of 10)
Metric Scale
Architectural Scale (Fractional divisions)
Combination Scale

**3. **Mechanical Engineer’s Scale Mechanical Drawings are drawn in inches.
16 Divisions per inch
Scales
1:1 Full Size
1:2 Half Size
1:4 Quarter Size
1:8 One Eight Size

**4. **Civil Engineer’s Scale Civil Drawings are drawn in feet as the base unit.
Scales commonly used
1”:10’ 1”:100’
1”:20’ 1”:200’
1”:30’ 1”:300’
1”:40’ 1”:400’
1”:50’ 1”:500’
1”:60’ 1”:600’

**5. **Metric Scale Metric Mechanical Drawings are drawn in inches.
Metric Civil Drawings are drawn in meters.
Scale
1:1 Full Size
1:2 Half Size
1:5 Fifth Size
1:10 Tenth Size

**6. **Drawing Scale We use scale in drawing to represent objects in the appropriate size on our drawing sheet.
We can represent large objects on a B-Size sheet using scale. (1” = 50’)
We can represent small objects on B-Size Sheet using scale. (4:1)
What are some examples that you might want to represent in a drawing?

**7. **Drawing Scales are Ratios Drawing Size : Actual Size
A rectangular box on a drawing with the scale of 2:1 has the measured dimensions 10” W x 16” L x 20” H. How large is the actual box?

**8. **Drawing Scales are Ratios Drawing Size : Actual Size
You are looking at drawings for a proposed golf course. The distance from the tee-box to the hole is 12 inches. If the scale on the drawing is 1”:50’, how far is it from the tee-box to the hole.

**9. **Understanding Projections Behind every 2D drawing of an object is a space relationship involving the object and three “imagined” things:
The observer’s eye or station point
The plane of projection
The projectors
Also called visual rays or lines of sight

**10. **Types of Projection There are two main types of projection
Parallel projection – the projectors are parallel
Perspective projection – the projectors come together at the station point
Perspective drawings represent objects as we see them

**11. **Types of Projection

**12. **Types of Projection

**13. **Perspective Projection Perspective – The most realistic of the pictorial drawing styles because it is closest to the way that we see.
An ordinary photograph shows the view in perspective.
We will not cover this view in this class.
You can study it on you own. See Chapter 16 in you text.
A drawing class would be another option.

**14. **Perspective Projection

**15. **Types of Parallel Projection Orthographic projections are a type of parallel projection
Orthographic (right angle) projections have parallel projectors that are perpendicular (90 degrees) to the plane of projection
In orthographic projection objects can be presented at true size or scaled at a proportion of their true size

**16. **Types of Orthographic Projection Multiview projection – A two dimensional representation of a three dimensional object.
It shows one or more necessary views of an object
Front, Rear, Top, Bottom, Right or Left

**17. **Multi-view drawing

**19. **Multiview DrawingsFirst- and Third-Angle Projection There are two main systems used for projecting and unfolding the views:
Third-angle projection which is used in the United States, Canada and some other countries
First-angle projection which is primarily used in Europe and Asia
You should understand both methods

**20. **Multiview DrawingsThird-angle Projection

**21. **Multiview DrawingsFirst-angle Projection

**22. **Types of Orthographic Projection Axonometric projections
Isometric, Dimetric, and Trimetric

**23. **Isometric Projection For a cube an isometric view obtained by first looking straight towards one face. Next the cube is rotated ±45° about the vertical axis, followed by a rotation of approximately ±35.264° (precisely arcsin(tan 30°) ) about the horizontal axis

**24. **Isometric Drawings

**25. **Isometric Grid - 30°

**26. **Types of Parallel Projection Oblique projection – when projectors are parallel to each other but are at an angle other than 90 degrees to the plane of projection
Oblique projections are commonly drawn at a 45° angle from the plane of projection.

**27. **Oblique Projection

**28. **Pictorial Projections Reviewed

**29. **Types of Projection Technical drawings of 3D objects usually use one of four standard types of projection
Multiview
Axonometric
Oblique
Perspective