sketching and sketching technique

Sketching

Contents PurposeTechniquesSize and ProportionAlphabet of LinesProjectionsReferences

PURPOSE

Purpose• 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.

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Purpose• 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

Shows design details

Size requiremen

ts.

Initialed and dated.

Title

TECHNIQUES

Contents

Sketching Techniques• Line Types:

Vertical LineInclined Line

Horizontal line

Sketching Techniques• Finding the slope angle of an inclined line:

Run = 4Rise = 2

Note: Rise and Run unitsdo not matter (As long as theunits are the same). You are finding an angle. In the above case, we are counting grid boxes.

Equation:tans = RISE/RUN

tans = 2/4tans = .5

s = arctan .5

Sketching Techniques• Sketching a Line.

Sketching Techniques• Sketching an Arc

Sketching Techniques• Sketching an Arc

Sketching Techniques• Sketching a Circle

1) Setup the diameter

2) Square in the diameter

3) Sketch diagonals

Sketching Techniques• Sketching a Circle4) Identify triangle centers

5) Sketch arcs

Sketching Techniques• Precision Measurement

– Refer to Presentation in Principles of Engineering

SIZE AND PROPORTION

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.

Size and Proportion• How to create proper size and proportion. Technique I– Using a pencil to measure.

Figure 2

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. Thisdistance will be used as a reference for sketching the restof 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 3

As you see in the completed house in Figure 3, the units of the numbered dimensionsare in windows.You should also notice thatthe use of graph paper also helps in creating proper sizeand proportion.

Size and Proportion• How to create proper size and proportion. Technique II– Boxing in the sketch.

In Figure 4 we are sketchinga chair. We sketch the boxesto the largest outside dimensions of our final object. Notice that light construction lines are alsoused to help guide us tothe proper size and proportion.

Figure 4

Size and Proportion• How to create proper size and proportion. Technique II– Boxing in the sketch.

Finally we use our sketchingtechniques for drawing arcs,lines and circles to completeour chair in Figure 5. Notice the box we started with is still existent as light construction lines. These areour guides for proportion andsize. Figure

5

ALPAHBET OF LINESConstruction Line: Very lightly drawn lines used as guides to help draw all other lines and shapes properly. Usually erased after being used.

Alphabet of Lines

Section Lines:Lines are used to

define where there is material after a part of the object is cut away.

Center Line: Lines that define

the center of arcs, circles, or symmetrical parts.They are half as thick as an object line.

Short Break Line: A freehanddrawn line that shows where a part is broken to reveal detail behind the part or to shorten a long continuous part. (Seeexample of Long Break Lineon the next slide.)

Hidden Line: Lines used to show interior detail that is not visible from the outside of the part.

Object Line: Thick lines

about .6mm(.032in) that show the visible edges of

an object.

Alphabet of LinesDimension 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 thisline to let you know the distance being communicated. Dimension lines are used in conjunction With extension lines to properly dimension objects.

Long Break Lines: Break lines are usedto either show detail or as in this case they canbe used to shorten very long objects thatdo not change in detail. Notice that this part is 12” long however we have shortenedthe drawing with break lines to use our space more efficiently.

How many lines from

the previous

slide can you identify here?

Leader Lines: Leader lines are used toshow 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 drawnwith a note at the end telling information

about what is being pointed at.

Extension Lines: Lines used to show where

a dimension starts and stops on an object.

Used with dimension lines to properly

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

part as to not get confused with the

object lines

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.

Alphabet of lines

How many lines from the previous 2 slides can you identify here?

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 position.

PROJECTIONS

Pictorial• Pictorial sketches are sketches that

show height, width, and depth all in one view. There are three common types:– Isometric– Oblique – Perspective

IsometricNote one

view shows height

width and depth.

Width and depth linesare drawn at 30 degrees from

the horizon line.

Oblique

Width lines areparallel with the horizon.

Front view is

truesize and

shape.

Front view is

truesize and shape.

In Cavalier Oblique depth

is full size. This cube

has the same height, width

and depth dimensions

Depth in an oblique

pictorial is distorted.

Easiest of the

pictorialsto draw.

Oblique

Front view is truesize and shape.

Width lines are

parallel with the

horizon.

In Cabinet Oblique depth

is half size. This allows the view

to look more realistic.

Perspective• 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

Note: The vanishingpoint in this sample is chosen for demonstration.

All lines in the depth project

to one point (vanishing

point). The location of the

vanishing point is based

on your line of sight.

Two Point Perspective

In two point perspective

the depth lines converge on one

vanishing point (VP2) and thewidth lines converge

on theother vanishing point

(VP1).

Shading• 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)

Shading(Stipple Shading)

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.

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 Drawings)

The arrows represent the line of sight associated

with each view.

Use the button below to jumpbetween thisview and the

orthoview on the

nextpage.

Orthographic Principal Views

Views are projected onto planes that exist on the face of that view. Arrows show the direction of the projection

Note how the viewsare oriented. Each

view isadjacent to the other

asif they were unfolded

from a 3D shape.

Front, Top and Right

views are used most

often. You can see how other

views resemblethese three

except they are not

as clear due to hidden lines.

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 In 3rd angle

projection, the projection planes usedto create views

are as shown in red.

Top

Front

Right Side

This sketch shows the quadrants where the

anglesof projection

are made from

Orthographic 3rd Angle Projection

ISO Symbol

Views are projected onto

planes that exist on the face of that view. Arrows show the direction of the

projection

Orthographic Spacial Quadrants and Planes

In 1st angle projection

the projection planes used to

create the views are

as shown in red.

Top

Front

Side

Orthographic 1st Angle Projection

ISO Symbol

Views are projected onto planes that exist on the opposite face of the view you want to display.The arrows show the directionof the projection.

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 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.

Orthographic View Selection

Longest Dimension

Most natural

position.

No hidden lines.

Best shape description

.

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 SelectionTwo views

will be identical

All dimensions

easilyshown on one view.

Uniform shape.

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 left.

Two View Selection

Symmetrical parts. A third view would be identical to the

other views

Second view is necessary for

depth.

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 Lines

An object line here takes precedenceover the center line. However wedraw short thin lines beyond the object to show there is a center lineunderneath 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

References• 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.

References•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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