Class 6 presentation

2D ESSENTIALSInstructor: Laura Gerold, PE

Catalog #10614113Class # 22784, 24113, 24136, & 24138

Class Start: January 18, 2012 Class End: May 16, 2012

QUESTIONS?

Accuracy

Standard – draw (and round) to two decimal places. Never draw or round to greater than three decimal places

Steel Fabrication tolerances is 1/8 and Engineered wood trusses are 1/16, you do not want to be any larger than the actual material sizes

When drawing or designing new detail or plan for scales ¾ and smaller round to a ¼”, 1” to full scale, 1/16” is the smallest. Materials suppliers do not round their products lower then 1/16.

When field dimensioning an existing building round to the nearest ¼”, because it is easier to do a dimension check right at the site.

I have seen spotted elevations on site plans round their plans to 3 decimal point. Example 1’-4” = 1.333’

CHAPTER 4 – GEOMETRIC

CONSTRUCTION WRAP-UP

BISECTING A LINE OR CIRCULAR ARC

From A ad B draw equal arcs with radius greater than half AB

Join Intersection D and E with a straight line to locate center C

Compass system

BISECTING AN ANGLE

1. Lightly draw arc CR 2. Lightly draw equal arcs r with radius

slightly larger than half BC, to intersect at D

3. Draw line AD, which bisects the angle

Practice

Draw a random line and a random angle Trade with your neighbor and bisect both

the line and the angle using the compass methods.

Check with your protractor and scale

Homework Help

Problem 4.30

CHAPTER 5 – ORTHOGRAPHIC

PROJECTION

Why do we need to learn about Orthographic Projection?

It’s a good way to understand how to draw three-dimension items as a 2-D sketch

Why do we need to learn about Orthographic Projection?

It’s used for a variety of applications including . . .

Architecture

Machine Design

Aviation Design

Prototypes

Toy (or Killer Robot?) Design

ETC . . .

UNDERSTANDING PROJECTIONS

To make and interpret drawings you need to know how to createprojections and understand the standard arrangement of views.

You also need to be familiar with the geometry of solid objects and be able to visualize a 3D object that is represented in a 2D sketch or drawing.

UNDERSTANDING PROJECTIONS

Vanishing Points: An Introduction to Architectural Drawing

Projection Method

Projection of an Object

The outline on the plane of projection shows how the object appears to the observer. In orthographic projection, rays (or projectors) from all points on the edges or contours of the object extend parallel to each other and perpendicular to the plane of projection. The word orthographic means “at right angles.”

Horizontal and Profile Projection Planes

Specific names are given to the planes of projection. The front view is projected to the frontal plane. The top view is projected to the horizontal plane. The side view is projected to the profile plane.

Views of Objects

The system of views is called multiview projection. Each view provides certain definite information. For example, a front view shows the true shape and size of surfaces that are parallel to the front of the object.

Multiview ProjectionThe system of views is called multiview projection. Each view provides certain definite information.

The Six Standard ViewsAny object can be viewed from six mutually perpendicular directions,

Six Standard Views:1. Top (Plan)2. Bottom3. Right Side4. Left Side5. Front6. Rear

Revolving the Object to Produce Views

Revolving the Object to Produce Views. You can experience different views by revolving an object.

The Glass BoxOne way to understand the standard arrangement of views on the sheet of paper is to envision a glass box.

If planes of projection were placed parallel to each principal face of the object, they would form a box.

Unfolding the Glass Box

To organize the views of a 3D object on a flat sheet of paper, imagine the six planes of the glass box being unfolded to lie flat.

Note the six standard views (front, rear, top, bottom, right side, left side).

The Glass Box UnfoldedLines extend around the glass box from one view to another on the planes of projection. These are the projectors from a point in one view to the same point in another view.

The Orthographic ProjectionThe front, top, and right-side views of the object shown now without the folding lines.

Principal DimensionsThe three principal dimensions of an object are width, height, and depth.

The front view shows only the height and width of the object and not the depth. In fact, any principal view of a 3D object shows only two of the threeprincipal dimensions; the third is foundin an adjacent view. Height is shown inthe rear, left-side, front, and right-sideviews. Width is shown in the rear, top,front, and bottom views. Depth isshown in the left-side, top, right-side,and bottom views.

Group Activity

Break up into groups of 2-3 Use the blocks to create a new “part” or

“building” Sketch the six standard orthographic

views Label the principal dimensions as width,

depth, and height Prepare to present your views

Elevation?

On architectural plans, the term elevation is used for all views that show the height

The top view is often called the “plan view” on architectural and engineering drawings

Label your six standard views as either elevation or plan views if relevant

Necessary Views

The top, front, and right-side views, arranged together, are called the three regular views because they are the views most frequently used.

A sketch or drawing should contain only the views needed to clearly and completely describe the object.

Transferring Depth Dimensions

You can transfer dimensions between the top and side views either with dividers or with a scale.

The depth dimensions in the top and side views must correspond point-for-point. When using CAD or instruments, transfer these distances accurately.

You may find it convenient to use a 45° miter line to project dimensions between top and side views.

Transferring Depth Dimensions Using a Miter Line (Also see page 186 in

text) Place the miter line (fig. 5-10, view B) to the

right of the top view at a convenient distance, keeping the appearance of a balanced drawing

Draw light projection lines from the top view to the miter line (fig. 5-10, view C), then vertically downward (fig. 5-10, view D)

Using the front view, draw horizontal projection lines (fig. 5-10, view E) to the right, intersecting the vertical projection lines

The result of this procedure is the outline and placement of the right side view

Miter Line

Group Project – Transfer Dimensions

Using your block creation, transfer the dimensions for three views using both the scale and the miter methods

Third-Angle Projection

To understand the two systems, think of the vertical and horizontal planes of projection, as indefinite in extent and intersecting at 90° with each other; thefour angles produced are called the first, second, third, and fourth angles (similar to naming quadrants on a graph.) If theobject to be drawn is placed below the horizontal plane and behind the vertical plane, as in the glass box you saw earlier, the object is said to be in the third angle. In third-angle projection, the views are produced as if the observer is outside, looking in.Common in the US &

Canada Third Angle Projection

Position of the Side ViewSometimes, drawing three views using the conventional arrangement wastes space.

First-Angle ProjectionIf the object is placed above the horizontal plane and in front of the vertical plane, the object is in the first angle.

The biggest difference between third-angle projection and first-angle projection is how the planes of the glass box are unfolded.

Common in Europe & Asia

First Angle Projection

Differentiate between 1st and 3rd Angle Projection

Group Project Use transparencies to create 1st and 3rd Angle

projections of your block structure

Hidden LinesThick, dark lines represent features of the object that are directly visible. Dashed lines represent features that would be hidden behind other surfaces.

CenterlinesThe centerline pattern is used to:

• show the axis of symmetry for a feature or part• indicate a path of motion• show the location for bolt circles and other circular patterns

The centerline pattern is composed of three dashes: one long dash on each end with a short dash in the middle.

Hidden Line Techniques

A. Make a hidden line join a visible line, except when it causes the visible line to extend too far.

B. Make hidden lines intersect at L and T corners.

Hidden Line Techniques

C. Make visible line “jump” a visible line when possible.

D. Draw parallel hidden lines so that the dashes are staggered.

Hidden Line Techniques

E. & F. When two or three hidden lines meet at a point, join the dashes.

Hidden Line Techniques

G. Make a hidden line join a visible line, except when it causes the visible line to extend too far.

H. Draw hidden arcs with the arc joining the centerline. There should not be a gap between the arc and the centerline.

Group Project

Use the Hidden Line Techniques to draw a view with hidden lines of your block project

No hidden lines? Draw a view of a coffee mug with hidden lines.

PRECEDENCE OF LINES

A visible line always takes precedence over and covers up a centerline or a hidden line when they coincide in a view (A and B).

A hidden line takes precedence over a centerline (C).

Group Project

Look over your drawings for today and determine whether you followed the precedence of lines

Centerlines continued…

Centerlines (symbol: ) are used to indicate symmetrical axes of objects or features, bolt circles, and paths of motion.

VIEWS OF SURFACESThere are terms used for describing a surface’s orientation to the plane of projection. The three orientations that a plane surface can have to the plane of projection are normal, inclined, and oblique.

Note how a plane surface that is perpendicular to a plane of projectionappears on edge as a straight line

ANGLES

If an angle is in a normal plane (a plane parallel to a plane of projection) it will show true size on the plane of projection to which it is parallel.

SIMILAR SHAPES OF SURFACESIf a flat surface is viewed from several different positions, each view will show the same number of sides and a similar shape. This consistency of shapes is useful in analyzing views.

INTERPRETING VIEWS

One method of interpreting sketches is to reverse the mental process used in projecting them.

Two ViewsMany objects need only two views to clearly describe their shape. If an object requires only two views, and the left-side and right-side views show the object equally well, use the right-side view.

One-ViewOften, a single view supplemented by a note or by lettered symbols isEnough.

Choice of Front View

The view chosen for the front view in this case is the side, not the front, of the automobile.

What’s Next?

• Review for Test 1• Finish Chapter 5• Chapter 6 – 2D Drawing Representation

Questions?

On one of your sketches, answer the following two questions: What was the most useful thing that you

learned today? What do you still have questions about?

Homework

Read Chapter 6Chapter 5 Review Questions: 1, 2, 8.Chapter 5 Exercises: 5.1, 5.5 (1, 2, 3), 5.6 (1, 2 – no isometric drawing)