freehand sketching-introduction to mechanical engineering

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.