Freehand Sketching

Introduction to Mechanical Engineering

Fall 2004

Created by:

P.M. Larochelle & J.S. Ketchel

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

Freehand Sketching

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!

Freehand Sketching

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 Sketches

Types of Sketches Oblique

– Advantage: one true face– Disadvantage: not “photorealistic”

Isometric (a type of axonometric drawing) & Perspective– Advantage: easy to visualize the object– Disadvantage: no true face

Multi-View (orthographic)– Advantage: true faces– Disadvantage: hard to visualize

Isometric, oblique, and perspective sketches are methods of showing the object in a single view.

Freehand Sketching Freehand sketches are not sloppy!

Freehand Sketching When possible use the grid on your engineering paper!

Freehand Sketching

Outline the sketch– Use light lines– Show major edges and boundaries and then add

small details

Freehand Sketching

Shape the sketches– Add appropriate details– Darken object lines

Freehand Sketching

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

Freehand Sketching

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 Lockhard, 3rd edition. Prentice-Hall, 2004.

Technical Drawing by Giesecke, Mitchell, Spencer, Hill, Dygdon, and Novak, 9th edition. Macmillan, 1991.