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Forging new generations of engineers. Sketching. Purpose Techniques Size and Proportion Alphabet of Lines Projections References. Contents Click Shape to go to section. PURPOSE. Contents. Purpose.

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Contents click shape to go to section l.jpg



Size and Proportion

Alphabet of Lines



Contents Click Shape to go to section.

Purpose l.jpg


Purpose5 l.jpg

  • The main purpose of sketching is to convey ideas. Engineers have to use sketches to brainstorm ideas, as well as, to show others what they are working on or what should be designed. Sketches are also used to document measurements from the field before they are produced as solid models on the computer.

Do you want to be a good sketcher l.jpg









Do you want to be a good sketcher?

Purpose7 l.jpg

  • Proper documentation in a notebook is essential. When proper documentation is made, ideas are not lost and projects can be duplicated. Figure 1 is a sample from a notebook where a sketch was made and notes as well as dimensions have been documented.

Proposed notebook sample l.jpg
Proposed Notebook Sample

Size requirements.

Shows design details


Initialed and dated.

Techniques l.jpg


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Sketching Techniques

  • Line Types:

Inclined Line

Vertical Line

Horizontal Line

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Run = 4

Rise = 2

Sketching Techniques

  • Finding the slope angle of an inclined line:


tans = RISE/RUN

tans = 2/4

tans = .5

s = arctan .5

Note: Rise and Run units

do not matter (As long as the

units are the same). You are

finding an angle. In the above

case, we are counting grid boxes.

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Sketching Techniques

  • Sketching a Line.

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Sketching Techniques

  • Sketching an Arc

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Sketching Techniques

  • Sketching an Arc

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1) Setup the


2) Square in the


3) Sketch


Sketching Techniques

  • Sketching a Circle

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4) Identify triangle


5) Sketch arcs

Sketching Techniques

  • Sketching a Circle

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Sketching Techniques

  • Precision Measurement

    • Refer to Presentation in Principles of Engineering

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Size and Proportion

  • Although you have learned to draw lines and arcs, you can not communicate properly until you understand how to sketch with the correct size and proportion. Without proper size and proportion your sketch will not look right.

  • Size: Length, width, height, distance. How big is the object you are sketching?

  • Proportion: If two objects are five feet apart in real life, then those two objects must appear to be five feet apart in your sketch.

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Hold your pencil at arms

length as you see in Figure 2.

Use the top of the pencil and

your thumb as a distance for

the height of the window. This

distance will be used as a

reference for sketching the rest

of the house as we did in the

house on the next slide.

Size and Proportion

  • How to create proper size and proportion.

    Technique I

    • Using a pencil to measure.

Figure 2

Size and proportion21 l.jpg

Figure 3

Size and Proportion

  • How to create proper size and proportion.

    Technique I

    • Using a pencil to measure.

As you see in the completed

house in Figure 3, the units

of the numbered dimensions

are in windows.

You should also notice that

the use of graph paper also

helps in creating proper size

and proportion.

Size and proportion22 l.jpg

Figure 4

Size and Proportion

  • How to create proper size and proportion.

    Technique II

    • Boxing in the sketch.

In Figure 4 we are sketching

a chair. We sketch the boxes

to the largest outside

dimensions of our final

object. Notice that light

construction lines are also

used to help guide us to

the proper size and


Size and proportion23 l.jpg

Figure 5

Size and Proportion

  • How to create proper size and proportion.

    Technique II

    • Boxing in the sketch.

Finally we use our sketching

techniques for drawing arcs,

lines and circles to complete

our chair in Figure 5.

Notice the box we started

with is still existent as light

construction lines. These are

our guides for proportion and


Alphabet of lines l.jpg

Object Line: Thick lines

about .6mm(.032in) that show

the visible edges of an object.

Alphabet of Lines

Short Break Line: A freehand

drawn line that shows where a part is

broken to reveal detail behind the part or

to shorten a long continuous part. (See

example of Long Break Line

on the next slide.)

Hidden Line: Lines used to

show interior detail that is not visible

from the outside of the part.

Center Line: Lines that define

the center of arcs, circles, or symmetrical parts.

They are half as thick as an object line.

Section Lines: Lines are used to

define where there is material

after a part of the object is cut away.

Construction Line: Very lightly

drawn lines used as guides to help draw

all other lines and shapes properly.

Usually erased after being used.

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Alphabet of Lines

Long Break Lines: Break lines are used

to either show detail or as in this case they can

be used to shorten very long objects that

do not change in detail. Notice that this part

is 12” long however we have shortened

the drawing with break lines to use

our space more efficiently.

Dimension Lines: Lines that are used to

show distance. Arrows are drawn on the

ends to show where the dimension line starts and ends.

The actual distance is usually located in the middle of this

line to let you know the distance being communicated.

Dimension lines are used in conjunction

with extension lines to properly

dimension objects.

Cutting Plane Line: A line used to

designate where a part has been cut

away to see detail. The arrows should

point in the direction that you are

looking at the cutout.

Extension Lines: Lines used to show where

a dimension starts and stops on an object.

Used with dimension lines to properly dimension

an object. The line is 1/16” away from the

part as to not get confused with the object lines

Leader Lines: Leader lines are used to

show dimensions of arcs, circles and to help

show detail. An arrow head is used to point

to the part you are dimensioning and the line comes

off the arrow point usually at a 45 degree angle.

At the end of this line a horizontal line is drawn

with a note at the end telling information

about what is being pointed at.

How many lines from the

previous slide can you identify


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Alphabet of lines

Phantom Lines: Phantom lines are used

to identify alternate positions that a part my

take up. In this example we are using Phantom

lines to show that the door handle may only move

45 degrees from it’s horizontal


How many lines from the

previous 2 slides can you

identify here?

Projections l.jpg


Pictorial l.jpg

  • Pictorial sketches are sketches that show height, width, and depth all in one view. There are three common types:

    • Isometric

    • Oblique

    • Perspective

Isometric l.jpg

Width and depth lines

are drawn at 30 degrees from

the horizon line.


Note one view shows

height width and depth.

Oblique l.jpg

Front view is true

size and shape.

Width lines are

parallel with the


In Cavalier Oblique depth

is full size. This cube

has the same height, width

and depth dimensions

Depth in an oblique

pictorial is


Easiest of the pictorials

to draw.

Depth lines are drawn

at an angle with the


Oblique32 l.jpg

Width lines are

parallel with the


In Cabinet Oblique depth

is half size. This allows the view

to look more realistic.

Front view is true

size and shape.


Perspective l.jpg

  • Perspective is a way to draw that shows a view of the object in the most realistic way. Vanishing points are used to guide the lines in the object to the horizon line or the horizontal line you see at your line of sight. We will discuss one and two point perspective.

One point perspective l.jpg
One Point Perspective

All lines in the depth project

to one point (vanishing

point). The location of the

vanishing point is based

on your line of sight.

Note: The vanishing

point in this sample

is chosen for


Two point perspective l.jpg
Two Point Perspective

In two point perspective

the depth lines converge on one

vanishing point (VP2) and the

width lines converge on the

other vanishing point (VP1).

Shading l.jpg

  • Shading allows us to create a more realistic image by showing how light reflects on the object. We use shading in engineering graphics to show features not easily seen otherwise. There are two main types of shading:

    • Straight Line

    • Stippling

Shading straight line l.jpg
Shading (Straight Line)

Shading stipple shading l.jpg
Shading(Stipple Shading)

Orthographic multiview drawings l.jpg
Orthographic (Multiview Drawings)

  • Pictorial sketches are great for engineers to explain ideas and communicate what the final part will look like to the customer. Unfortunately, pictorial drawings have some disadvantages. Foreshortened views and distorted features do not allow for accurate prototyping. Many times, for parts to be accurately depicted, you need straight on views of each surface.

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Orthographic (Multiview Drawings)

  • In order to obtain these straight line views we have a type of drawing called Orthographic Projection also known as Multiview drawings. Orthographic projection is a way to project a view based on a line of sight that is perpendicular to that view. There are six of these views to any object as shown in the next slide.

Orthographic multiview drawings41 l.jpg
Orthographic (Multiview Drawings)

The arrows represent the

line of sight associated

with each view.

Use the button

below to jump

between this

view and the ortho

view on the next



Orthographic principal views l.jpg
Orthographic Principal Views

Note how the views

are oriented. Each view is

adjacent to the other as

if they were unfolded

from a 3D shape.


Top and Right views

are used most often. You can

see how other views resemble

these three except they are not

as clear due to hidden lines.

Click to go back

to ISO view.


Orthographic angle of projection l.jpg
Orthographic Angle of Projection

  • The example you have just seen is shown in the third angle of projection. This is the standard in the United States and Canada. The rest of the world draws in the first angle of projection. The following slides will show how the views are derived and what they look like.

Orthographic spacial quadrants and planes l.jpg

In 3rd angle projection,

the projection planes used

to create views are

as shown in red.



Right Side

Orthographic Spacial Quadrants and Planes

This sketch shows the

quadrants where the angles

of projection are made from

Orthographic 3rd angle projection l.jpg
Orthographic 3rd Angle Projection

Views are projected onto planes

that exist on the face of that view.

Arrows show the direction of the


ISO Symbol


Orthographic spacial quadrants and planes46 l.jpg



In 1st angle projection

the projection planes used to

create the views are

as shown in red.


Orthographic Spacial Quadrants and Planes

Orthographic 1st angle projection l.jpg
Orthographic 1st Angle Projection

Views are projected onto planes

that exist on the opposite face of the

view you want to display. The

arrows show the direction

of the projection.

ISO Symbol


Orthographic view selection l.jpg
Orthographic View Selection

  • Finding the best view of a part can be difficult. Two or more sides may look like the best solution for a front view. On the next slide is a list of characteristics that you should use in choosing your views.

Orthographic view selection49 l.jpg
Orthographic View Selection

  • Steps in selecting the front.

    • Most natural position or use.

    • Shows best shape and characteristic contours.

    • Longest dimensions.

    • Fewest hidden lines.

    • Most stable and natural position.

    • Relationship of other views

      • Most contours.

      • Longest side.

      • Least hidden lines.

      • Best natural position.

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Orthographic View Selection

Most natural position.

Longest Dimension

Best shape description.

No hidden lines.

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Orthographic View Selection Numbers

  • Another decision on view selection you need to make is how many views. You usually do not need more than three but you may only need one or two. The following slides will show when to make a decision between one, and two view drawings.

One view selection l.jpg
One View Selection

Two views

will be identical

Uniform shape.

All dimensions easily

shown on one view.

One view selection53 l.jpg
One View Selection

It is also possible to

have one view drawings

of objects that are flat

and have even thickness.

Gauges and gaskets are

two such objects. We

have a gauge here on the


Two view selection l.jpg
Two View Selection

Symmetrical parts. A third view

would be identical to the other


Second view is necessary for


Precedence of lines l.jpg
Precedence of Lines

  • In multiple view drawings, many times different line types will take up the same space, therefore, we have line precedence. The following is an explanation of which lines exist over others.

    • Object lines over hidden and center.

    • Hidden over center.

    • Cutting plane lines over center lines.

  • The following slide will show an example.

Precedence of lines56 l.jpg
Precedence of Lines

An object line here takes precedence

over the center line. However we

draw short thin lines beyond the

object to show there is a center line

underneath the object line.

Object lines took precedence over

the hidden lines you would see

from the hole. The center line in

the top view would show the depth

of the hole as well as the right

side view.

References l.jpg


References58 l.jpg

  • Madsen, David A., Shumaker, Terence M., Stark, Catherine, Turpin, J. Lee, Engineering Drawing and Design Second Edition,Delmar Publishers, 1996, ISBN 0-8273-6720-1.

  • Brown, David, You Can Draw,North Light Books, Cincinnati, Ohio, 1986, ISBN 0-89134-216-8.

  • Olivo, Dr. C. Thomas, Olivo, Thomas P., Basic Blueprint Reading and Sketching Sixth Edition, Delmar Publishers Inc., 1993, ISBN 0-8273-5740-0.

  • Johnson, Cindy M., Lockhart, Shawna D., Engineering Design Communication, Prentice Hall, 2000, ISBN 0-201-33151-9.

References59 l.jpg

  • Spencer, Henry Cecil, Dygdon, John Thomas, Novak, James E; Basic Technical Drawing 6th Edition; Glencoe McGraw Hill; New York, New York,1995, ISBN 0-02-685660-3.

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Do you want to be a good sketcher?

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