PROJECTIONS

11.2

PROJECTIONS

DEF: a projection is a representation of a three-dimensional shape on a two-dimensional surface.

PROJECTIONSProjections are arranged into 3 categories:

1. multi-view2. Isometric3. oblique

An example of an isometric projection

DRAWING TERMINOLOGYOBSERVATORY p., 343

PROJECTIONS DIFFER IN 2 ASPECTS:

DIFFERENCE #1

• Position of the object with respect to the surface it is drawn on.

DIFFERENCE #2

• Angle between the visual rays & the sheet of paper.

The table on the next slide will illustrate these differences.

COMMON TYPES OF PROJECTIONSOBSERVATORY p., 344

ORTHOGONAL PROJECTIONS

DEF: an orthogonal projection is a projection in which the visual rays are perpendicular from the surface of the paper.

PROJECTIONS

PROJECTIONS

ORTHOGONAL

MULTI-VIEW ISOMETRIC

OBLIQUE

ISOMETRIC vs. OBLIQUE

ISOMETRIC OBLIQUE

ISOMETRIC PROJECTIONS

DEF: an isometric projection is a “perspective” drawing of an object where the principal edges are arranged on 3 isometric angles (120o degrees).

ISOMETRIC PROJECTIONS

OBSERVATORY p., 347 OBSERVATORY p., 347

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We will illustrate the main stages of isometric drawing of the object shown above in multi-view. We will use a method called box construction.

To create the box, use construction lines to outline an isometric box as large as the overall object to be drawn.

The vertical axis is equal to the real height.

The two other axes, drawn at 30° to horizontal, correspond to the actual width and length of the object.

Isometric drawing

Isometric drawing

The object is drawn by removing volumes from the box.

A 30º- 60º set square is used to trace the isometric lines.

The box is an isometric drawing as large as the overall object to be shown. Its lines are drawn very faintly.

Measurements are reported on the isometric axes, or on lines parallel to these axes.

Isometric drawing

The object is drawn by removing volumes from the box.

A 30º- 60º set square is used to trace the isometric lines.

The box is an isometric drawing as large as the overall object to be shown. Its lines are drawn very faintly.

Measurements are reported on the isometric axes, or on lines parallel to these axes.

Isometric drawing

STAGE 1 STAGE 2 STAGE 3

Sketch the box.

STAGES OF DRAWING IN ISOMETRIC PERSPECTIVE

Measure on the axes and trace the details in construction lines.

Carry out the final layout.

Isometric drawing

STAGE 1 STAGE 2 STAGE 3

Sketch the box.

STAGES OF DRAWING IN ISOMETRIC PERSPECTIVE

Measure on the axes and trace the details in construction lines.

Carry out the final layout.

MULTI-VIEW PROJECTIONS

DEF: a multi-view projection is a 2-D representation of the different views on an object.

MULTI-VIEW PROJECTIONSOBSERVATORY P., 345

MULTI-VIEW PROJECTIONSOBSERVATORY P., 346

Try it yourself!

• Begin working on the lab entitled projections. – Answer all questions on pages 1-2 and complete

the multi-view projection.

PERSEPCTIVEDrawings with “perspective” represent all 3 dimensions in a single view.

OBLIQUE PROJECTIONS

DEF: a perspective drawing in which one of the sides of the object is parallel to the paper, but the depth is represented by parallel lines drawn at oblique angles.

THE USE OF PROJECTIONS IN ENGINEERING DRAWINGS

3 main drawings used in an engineering projects are:

1. General2. Exploded views3. Detail Drawings

GENERAL DRAWINGSAn engineering drawing that shows the overall design of an object.

OBSERVATORY p., 349

EXPLODED-VIEW DRAWINGSAn engineering drawing that shows the different parts, or features, of the object separately.

OBSERVATORY p., 349

DETAIL DRAWINGSAn engineering drawing that specifies all of the details necessary to make a particular part of an object.

TYPES OF ENGINEERING DRAWINGSTYPE DESCRIPTION PROJECTION

General A drawing which shows the overall appearance of an object.

•Multi-view•Isometric

Exploded A drawing that illustrates the different parts of an object, separately. May include a list of materials.

•Isometric

Detail A drawing that contains all of the necessary elements to construct an object.

•Multi-view