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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 Engineers Scale (Division of 10) Metric Scale Architectural Scale (Fractional divisions) Combination Scale

    3. Mechanical Engineers 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 Engineers 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 observers 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 Drawings First- 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 Drawings Third-angle Projection

    21. Multiview Drawings First-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