1. ENS 207 engineering graphics
Lecture 2: sketching

2. 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.

3. TECHNIQUE OF LINES line patterns
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

4. 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 cutting-plane 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.

5. 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.

6. Edges and Vertices Edges Vertices Points
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.

7. For Example: 1. Visible 2. Hidden 3. Center
From Bertoline: Figure 2.38 / Pg 42
In engineering and technical drawing, it is important that hidden features be represented, so that the reader of the drawing can clearly understand the object.
Thus we need hidden lines to emphasize that those features exist and are hidden in that particular view.
We also need center lines to understand how the features defined in the 2D views translate into 3D.
NOTE: It must be emphasized that hidden lines and center lines are used only on Orthographic projection drawings, never on isometric drawings
Q: Do we need a convention for what line to show if two lines fall on top of each other?
A: Yes! Otherwise features which are more important (eg: visible lines) would be overridden by less important features (eg: hidden lines) and the resulting drawing would be interpreted inaccurately. The next slide shows the convention followed.
2. Hidden
3. Center

8. Horizontal line
Vertical line

9. 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

10. Arc Method 1 : Starting with a square
Method 2 : Starting with a center line

11. Example

13. 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.

14. CURVES
Curved shapes are best sketched by first defining points along the curve, then lightly sketching the curve between the points.

15. 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.

16. Introduction to Isometric Projection
CUBE
Isometric Projection:
One type of axonometric pictorial (3-D) projection
‘Iso-’ means ‘equal
‘metric projection’ means ‘a projection to a scaled measure’
The three dimensions are not only shown in one view, but also the dimensions can be scaled from this drawing
START WITH A CUBE
All of the normal drawing planes (top, front, side) are equally foreshortened or tilted, and all of the major axes (X, Y, Z) are at equal rotations from each other (120 degrees apart), as in the illustration above.
And, because all of the major planes are equally foreshortened, all of the measurements in these planes are equal as well as shown above. This means that the same measuring scale may be used in drawing both the width, height, and depth of objects.
Isometric means equal measure
All planes are equally or proportionately shortened and
tilted
All the major axes (X, Y, Z) are 120 degrees apart
AU 2005

17. Making an Isometric Sketch
Defining Axis
30o
60o
Isometric Axis
Derive the axes from a vertex of the cube
AU 2005

18. Three planes The three planes of an isometric axis are defined as the
left, right, and top planes, respectively

19. Making an Isometric Sketch
Axis Convention
Height
Choose the longest dimension to be the width (or the depth) for optical stability
Width
Depth
The above slide is used to indicate the manner in which the width, depth and height of a 3-dimensional object is seen in an Isometric Sketch.
Note the assignments of height, width, and depth to the axis.
The front view direction is shown. Please emphasize this convention to the students.
Front view
Isometric Axis Convention
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20. Object for Practice
How to derive this object from a rectangular piece of wood?
Shape it in to a rectangle with maximum dimensions (so as to fit the required object) on the three axes
Chisel out the unwanted parts…. Slides follow.
NOTE: No scale provided due to lack of measurements of blocks.
TA’s – Get the blocks from the Instructors Console and distribute them to all the tables.
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21. Blocking in the Object Begin with Front Face
Height
Width
Identify the size of the front view of the object and sketch its outside dimensions on the Isometric view.
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22. Blocking in the Object: Add Side Face
Height
Depth
Side Face
Once the front view outside dimensions are added on the isometric sketch, add the side view dimensions.
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23. Blocking in the Object: Add Top Face
After front and side views are sketched on the isometric drawing, then add the top view.
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24. Adding Detail Cut Outs – Part 1
The order of adding the details is important. They build upon each other.
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25. Adding Detail Cut Outs – Part 2
Note that lines parallel to axes
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26. Adding Detail Cut Outs – Part 3
Note that lines parallel to axes are drawn first, then oblique lines are determined from their intersections.
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27. Darken Final Lines - Part 4
Note:
All visible edges
will be darkened
Construction lines can be left in but must be much lighter than the final lines.
AU 2005

28. 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.