ENS 207 ENGINEERING GRAPHICS
LECTURE 2: SKETCHING
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Freehand Sketching
Freehand sketches are a helpful way to organize your thoughts
and record ideas. They provide a quick, low-cost way to explore
various solutions to design problems so that the best choices can
be made.
TECHNIQUE OF LINES
The chief difference between a drawing and a freehand sketch lies in the character
or technique of the lines.
A good freehand line is not
expected to be as rigidly straight
or exactly uniform. A good
freehand line shows freedom and
variety, whereas a line drawn
using CAD or instruments should
be exact.
line patterns
Lineweights
Even in freehand drawings, thick lines should be twice the width of thin lines.
Thicknesses do not have to be exact, but there should be an obvious
difference between thick and thin lines. Because visible lines and cuttingplane lines are the two thick line patterns, other lines should be distinctly
thinner in comparison.
To draw thick and thin lines freehand,
you might like to keep two pencils
handy, one that is razor sharp for thin
lines and another that is dulled, to
create thicker lines. As the sharp point
becomes dulled, switch it with the
dull pencil, and sharpen the other,
so that there is always one sharp
and one dulled point ready to use.
FREEHAND LINES
The main difference between an instrument or CAD drawing and a freehand
sketch is in the appearance of the lines. A good freehand line is not expected to
be precisely straight or exactly uniform, as is a CAD or instrument-drawn line.
Freehand lines show freedom and variety.
Freehand construction lines are very light, rough lines. All
other lines should be dark and clean.
Edges and Vertices
Edges
An edge of the solid is formed where two
surfaces intersect. Edges are represented in
drawings by visible or hidden lines.
Vertices
A vertex (plural, vertices) of a solid is
formed where three or more surfaces
intersect..
Points
A point is used to represent a location in space
but has no width, height, or depth.
For Example:
1. Visible
2. Hidden
3. Center
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Horizontal line
Vertical line
Small Circle
Method 1 : Starting with a square
1. Lightly sketching the square and marking the mid-points.
2. Draw light diagonals and mark the estimated radius.
3. Draw the circle through the eight points.
Step 1
Step 2
Step 3
Arc
Method 1 : Starting with a square
Method 2 : Starting with a center line
Example
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PROPORTIONS
Sketches should be proportional. A square should look like a square, and a
rectangle like a rectangle. Graph paper is very helpful in sketching
proportionally, but it is still sometimes difficult to be accurate even with graph
paper.
CURVES
Curved shapes are best sketched by first defining points along
the curve, then lightly sketching the curve between the points.
Circles and Ellipse
An ellipse can be sketched by first sketching a perpendicular axis, then
locating four marks on the centerlines that are approximately equal to
major and minor axis distances. Sketch a light curve, make any
corrections necessary, and
darken in the elliptical shape.
Introduction to Isometric Projection
CUBE
• Isometric means equal measure
• All planes are equally or proportionately shortened and
tilted
• All the major axes (X, Y, Z) are 120 degrees apart
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Making an Isometric Sketch
• Defining Axis
60o
30o
30o
Isometric Axis
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60o
Three planes
The three planes of an isometric axis are defined as the
left, right, and top planes, respectively
Making an Isometric Sketch
•
Axis Convention
Height
Choose the longest
dimension to be the width
(or the depth) for optical
stability
Width
Front view
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Depth
Isometric Axis Convention
Object for Practice
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Blocking in the Object
Begin with Front Face
Front Face
Height
Width
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Blocking in the Object: Add Side
Face
Side Face
Height
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Depth
Blocking in the Object: Add Top Face
Top Face
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Adding Detail Cut Outs – Part 1
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Adding Detail Cut Outs – Part 2
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Adding Detail Cut Outs – Part 3
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Darken Final Lines - Part 4
Note:
All visible edges
will be darkened
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PLANNING YOUR DRAWING OR SKETCH
When laying out a drawing sheet, you will
need to consider:
• the size and scale of the object you will
show
• the sheet size
• the measurement system (units) for the
drawing
• the space necessary for standard notes
and title block.