freehand sketching-introduction to mechanical engineering
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Freehand Sketching
Freehand Sketching● Ideation – Integral to the design process
– Generation of design concepts to solve a design problem● Usually freehand sketching is used to explore, study and
communicate these design concepts● Even today, and for the foreseeable future, many great
design ideas are communicated via freehand sketching● The “BEST” design engineers can immediately
communicate an idea via a freehand sketch
● Required– Pencil, Paper and Eraser
● Do not use– Straight edges, templates, compasses etc.
They slow down the process and defeat the purpose of fast communication of ideas!
● Sketches are planned● Visualize the sketch
– Size of paper & scale– Orientation of the object– Minimum detail to communicate the idea– Type of sketch● Oblique● Isometric● Orthographic
Types of SketchesOblique
Advantage: one true faceDisadvantage: not “photorealistic”
Isometric (a type of axonometric drawing) & PerspectiveAdvantage: easy to visualize the objectDisadvantage: no true face
Multi-View (orthographic)Advantage: true facesDisadvantage: hard to visualize
Isometric, oblique, and perspectivesketches are methods of showing the object in a single view.
● Freehand sketches are not sloppy!
● When possible use the grid on your engineering paper!
● Outline the sketch– Use light lines– Show major edges and boundaries and then add small
details
● Shape the sketches– Add appropriate details– Darken object lines
● Fundamental Rule of Sketching– Maintain Proportion
● Hints: use standard techniques to draw lines and arcs
● Lines– Locate a start “dot”– Locate an end “dot”– Put pencil on start dot, look at the end dot and
smoothly move pencil toward the end dot
● Circles (arcs)– Draw light horizontal and vertical lines that
intersect at the center– Lightly mark the radius on the lines– Connect the radius marks with arcs to
complete the circle– See Step-by-Step 3.1& 3.3 on pages 60 & 62.
Construction Lines● Light and thin lines● Serve as path for final straight lines● Intersection of construction lines specify the
length of the final lines● Points marked by the intersection of
construction lines serve as guides for sketching of arcs and circles
● Guide the proportion of the sketch
Linetypes
Examples of Good Freehand Sketching Technique
Oblique Sketching● Step 1 – Draw the horizontal and vertical
construction lines which outline the basic shape of the main face - “Blocking in”
● Step 2 – Sketch the face of the part● Step 3 – Sketch receding construction lines at
30 or 45 degrees● Step 4 – Sketch- in and darken the lines
outlining the part – Done!
Isometric Sketching
● Step 1 – Construct a horizontal line, two lines at 30 degrees above the horizontal and a vertical line through their intersection– This defines the isometric axes used to draw
the sketch
Isometric Sketching
● Step 2 – Sketch in a box to “block-in” the front face and the other faces follow
● Step 3 – Sketch the outline of the front face in it’s “block” and the other faces follow– Work parallel to the isometric axes
References
● Chapter 3 of Modern Graphics Communication by Giesecke, Mitchell, Spencer, Hill, Dygdon, Novak, and Lockhart, 3rd edition. Prentice-Hall, 2004.
● Technical Drawing by Giesecke, Mitchell, Spencer, Hill, Dygdon, and Novak, 9th edition. Macmillan, 1991.