Orthographic Drawing

Orthographic Projection An orthographic projection is a 2 dimensional representation of a 3 dimensional object.

Six Principle Views Any object can be viewed from six perpendicular views

The Glass Box One 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 Method Glass 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 Method The 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 Views When 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 Views You 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 Views Top 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 Plane Normal 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 Plane Inclined 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 Planes Oblique 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 Lines Identify the foreshortened lines in the orthographic projection below.

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

Axis and Center Lines The 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 View Considerations when choosing the front view of an object. Chose the view that shows the most features or characteristics of the object Choose 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 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

Third-angle Projection

First-angle Projection

Hidden Lines An advantage of orthographic views is that each view shows the object all the way through as if it were transparent Thick dark lines represent visible features Dashed lines represent features that would be hidden behind other surfaces When possible, choose views that show features with visible lines

Rules for drawing hidden lines.

Centerlines The centerline is used to: Show the axis of symmetry of a feature or part Indicate a path of motion Show the location for bolt circles or other circular patterns The centerline pattern is composed of three dashes, one long dash on each end with a short dash in the middle

Centerlines

Precedence of Lines When lines coincide on a drawing the rules of precedence are: Visible lines always take precedence over hidden or centerlines Hidden lines take precedence over centerlines

Precedence of Lines

Drawing Pencils ENGR 123 Drawing Conventions Section Lines = 0.5 mm HB Visible Lines = 0.7 mm HB Hidden Lines = 0.5 mm HB Centerlines = 0.5mm HB Construction Lines = 0.5mm 2H

Lines Types and Order of Precedence 1 0.7 mm 2 0.5 mm 0.5 mm 3

Planning Your Drawing or Sketch When laying out a drawing sheet you will need to consider: Size and scale of the object Sheet size Measurement system Space 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 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