Orthographic Projection – Multi-View Drawing

Orthographic Projection

a system of drawing views of an object using perpendicular projectors from the object to a plane of projection

Revolving an Object to Produce the Six Basic Views

Projection of an Object

The Glass Box

• Imagine that the object you are going to draw is positioned inside a glass box, so that the large flat surfaces of the object are parallel to the walls of the box.

• From each point on the object, imagine a ray, or projector perpendicular to the wall of the box forming the view of the object on that wall or projection plane.

The Glass Box

Unfolding the Glass Box

The Six Basic Views

Why must views be arranged so that they align?To make it possible for someone to interpret the drawing.

TOPLEFT FRONT RIGHT

BOTTOM REAR

The Standard Arrangement of Views

Transferring Dimensions

Using a Miter Line to Transfer Depth1.

Draw miter line at 45 degreesat a convenient distance to produce the desired view.

2. Sketch light lines projecting depth locations for points to miter line and then down into side view as shown.

3. Project additional points, surface by surface.

4. Draw the view locating each vertex of the surface on the projection and miter line.

Symbols for 1st & 3rd Angle Projection

Third angle projection is usedin the U.S., and Canada

Other Visualization Tools

• Number vertices in different views of multiview and isometric drawing

• Practice

Multiview Sketching

• Represents a 3-D object with a series of 2-D views in contrast to “pictorials” which show all three dimensions in a single view

• Also called orthographic projection

Multiview DrawingMultiview Drawing

PictorialPictorial

Parallel projection• Preserves true relationship

between features– Lines that are parallel on the object

are parallel on the drawing

Parallel versus Perspective Projection

ParallelParallelParallelParallel

Projection Planes versus Views

• Projection planes: – Object formed from projection lines projected perpendicularly

onto a projection plane

– Planes: Horizontal, frontal, and profile

– Each projection plane is perpendicular to adjacent projection planes

• Principle views– The object is rotated 90 degrees about the horizontal or

vertical axis to give six principle views (top, bottom, front, rear, left, and right side)

– Common views: top, front, and right side

Only use Necessary Views • One view drawings

– Sphere (Football)

• Two view drawings– Cylindrical parts

– Show the circular and rectangular view

• Three view drawings– Usually sufficient for all other drawings

– Top, front, and right side view

Orientation and Placement of Views

• The most descriptive view should be selected as the front view

• The natural orientation of the part should be preserved if possible

• Views must be aligned– Top view above front view

– Right view to the right of front view

Hidden linesHidden lines• Represented with dashed

lines• Precedence of lines

(visible, hidden, center)• Views should be selected

to minimize the use of hidden lines most descriptive view should be selected as the front view

Fold Lines

• Represents a 90 degree fold between views • Generally not shown on engineering drawings

except when views other than the principle views (auxiliary views) are used.

Terminology to Relate Views

• Adjacent view– A view that is separated by a fold line

– The top view is an adjacent view to the front view

• Central View– A view that is between two adjacent views

– The front view is the central view of the top, front, and right side view

• Related views– Two views that are adjacent to a central view

– The top and right side view are related views since they are both adjacent to the front view

Constructing a New View

The top and front views of a surface are shown

The fold line represents a 90 degree fold between the views

Parallel projection lines are perpendicular to the fold line

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Constructing a New View A vertical fold line is drawn at an

arbitrary distance from the front view Parallel projection lines are drawn from

each vertex The common depth between the top and

side view is used to locate each vertex on the projection lines

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Sketching Allows for the Quick Translation of Thoughts to Paper

• Commit thoughts to paper before you lose an idea

• Avoid the of use mechanical tools (drawing tools are helpful for beginners)

• Does not need to be an exact representation– objects may be simplified

– parts may be missing

• Avoid erasing– as new ideas are developed make new sketches

– start with light lines and then darken with darker lead or heavier strokes

Summary

• The six standard views are often thought of as produced from an unfolded glass box.

• Distances can be transferred or projected from one view to another.

• Only the views necessary to fully describe the object should be drawn.