Orthographic ProjectionAn orthographic projection is a 2 dimensional

representation of a 3 dimensional object.

Six Principle ViewsAny object can be

viewed from six perpendicular views

The Glass BoxOne way to understand the standard

arrangement of views on a sheet of paper is to envision the object in a glass box

The outside observer would see six standard views of the object through the sides of this imaginary glass box

Glass Box MethodGlass Box Method:

The object is placed in a glass box. The image of the object is projected on the

sides of the box. The box is unfolded.The sides of the box are the principle views.

Glass Box MethodThe object is

placed in a glass box.

The side of the box represent the 6 principle planes.

Six Principle Views

Reading Isometric Sketches

Reading Isometric Sketches

Create the orthographic projections for the following object.

The height and depth of is equal to 3 grid squares.

Create the orthographic projections for the following object.

Number of Required ViewsWhen drawing an orthographic projection

you must include the appropriate number of views to fully describe the true shape of the part.

You may use a fewer number of views if you can fully describe the part in the given views.How many views are required to fully describe

a rectangular box?How many views are required to fully describe

a sphere?

Number of Required ViewsYou may use additional views, such as the

left, back, or bottom views to describe an object if the object cannot be fully described in the three standard views.

additional views such as section views, detail views and auxiliary views may also be drawn to fi.

Measurement Transfer Between ViewsMeasurement Transfer Between ViewsTop and Bottom

views show LENGTH and WIDTH.

Left and Right views show HEIGHT and WIDTH

Front and Rear views show HEIGHT and LENGTH.

The line (drawn at a 45° angle) is used to transfer depth measurements between the top and right side (or left side) views.

Normal PlaneNormal PlaneNormal Planes

will appear as an edge in two views and a true sized plan in the remaining view when using three views such as a top, front and right side.

Inclined PlaneInclined PlaneInclined Planes

will appear as an edge view in only one of the three views.

The inclined plane will appear as a rectangular surface in the other two views.

Oblique PlanesOblique PlanesOblique Planes

will not appear as an edge view in any of the six views since they are not parallel or perpendicular to the projection planes.

They always appear as a “plane” and have the same number of corners in each of the six views.

Foreshortened LinesIdentify the foreshortened lines in the orthographic projection below.

Curved SurfacesCurved SurfacesA cylinder

will appear as a circle in one view and a rectangular shape the other two views.

Axis and Center LinesAxis and Center LinesThe axis

appears where the cylinder appears rectangular.

Center marks are used to identify the center of the cylinder where it appears circular.

Choosing the Front ViewConsiderations when choosing the front view

of an object.Chose the view that shows the most features or

characteristics of the objectChoose the view that contains the least number

of hidden lines. Choose the view so the part is oriented with its

longest length parallel to the bottom of the drawing.

First- and Third-Angle ProjectionThere 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

Third-angle Projection

First-angle Projection

Hidden LinesAn advantage of orthographic views is that

each view shows the object all the way through as if it were transparentThick dark lines represent visible featuresDashed lines represent features that would be

hidden behind other surfacesWhen possible, choose views that show

features with visible lines

Rules for drawing hidden lines.

CenterlinesThe centerline is used to:

Show the axis of symmetry of a feature or part

Indicate a path of motionShow the location for bolt circles or other

circular patternsThe centerline pattern is composed of

three dashes, one long dash on each end with a short dash in the middle

Centerlines

Precedence of LinesWhen lines coincide on a drawing the rules of

precedence are:Visible lines always take precedence over

hidden or centerlinesHidden lines take precedence over centerlines

Precedence of Lines

Drawing PencilsENGR 123 Drawing Conventions

Section Lines = 0.5 mm HBVisible Lines = 0.7 mm HBHidden Lines = 0.5 mm HBCenterlines = 0.5mm HBConstruction Lines = 0.5mm 2H

Lines Types andOrder of Precedence

1

2

3

0.7 mm

0.5 mm

0.5 mm

Planning Your Drawing or SketchWhen laying out a drawing sheet you will

need to consider:Size and scale of the objectSheet sizeMeasurement systemSpace necessary for notes and title block

Putting it all together…Choose the front view.Determine the number of required views.Identify the scale.Draw visible lines for the front view.Project the feature to draw the top view.Draw the hidden lines.Draw the center lines and center marks.

Draw the orthographic projections needed to fully describe the part. Choose the best view for the front view. Use a scale of 1:1 with 2” spacing between the views