Sketching and sketching technique

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Transcript of Sketching and sketching technique

Sketching

Contents

PurposeTechniquesSize and ProportionAlphabet of LinesProjectionsReferences

PURPOSE

PurposeThe 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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PurposeProper 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 SampleShows design detailsSize requirements.Initialed and dated.Title

TECHNIQUESContents

Sketching TechniquesLine Types:

Vertical LineInclined Line

Horizontal line

Sketching TechniquesFinding 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/RUNtans = 2/4tans = .5s = arctan .5

Sketching TechniquesSketching a Line.

Sketching TechniquesSketching an Arc

Sketching TechniquesSketching an Arc

Sketching TechniquesSketching a Circle

1) Setup the diameter2) Square in the diameter3) Sketch diagonals

Sketching TechniquesSketching a Circle

4) Identify triangle centers5) Sketch arcs

Sketching TechniquesPrecision MeasurementRefer to Presentation in Principles of Engineering

SIZE AND PROPORTION

Size and ProportionAlthough 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 ProportionHow to create proper size and proportion. Technique IUsing 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 ProportionHow to create proper size and proportion. Technique IUsing a pencil to measure.

Figure 3As 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 ProportionHow to create proper size and proportion. Technique IIBoxing 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 ProportionHow to create proper size and proportion. Technique IIBoxing 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 LinesSection 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.

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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?

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Leader Lines: Leader lines are used toshow dimensions of arcs, circles and to help show detail. An arrow head is used to pointto the part you are dimensioning and the line comesoff 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.

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Extension Lines: Lines used to show wherea dimension starts and stops on an object. Used with dimension lines to properly dimensionan object. The line is 1/16 away from thepart 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.

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Alphabet of linesHow 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 its horizontal position.

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PROJECTIONS

PictorialPictorial sketches are sketches that show height, width, and depth all in one view. There are three common types:IsometricOblique Perspective

Isometric

Note 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 depthis full size. This cubehas the same height, widthand depth dimensionsDepth in an obliquepictorial is distorted.Easiest of the pictorialsto draw.

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Oblique

Front view is truesize and shape.Width lines areparallel with the horizon.In Cabinet Oblique depthis half size. This allows the viewto look more realistic.

PerspectivePerspective 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 projectto one point (vanishingpoint). The location of the vanishing point is basedon your line of sight.

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Two Point Perspective

In two point perspective the depth lines converge on onevanishing point (VP2) and thewidth lines converge on theother vanishing point (VP1).

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ShadingShading 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 LineStippling

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.

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Orthographic Principal Views

Views are projected onto planes that exist on the face of that view. Arrows show the direction of the projectionNote how the viewsare oriented. Each view isadjacent to the other asif they were unfolded from a 3D shape.

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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.

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Orthographic Angle of ProjectionThe 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.TopFrontRight SideThis 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

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Orthographic Spacial Quadrants and Planes

In 1st angle projection the projection planes used tocreate the views areas shown in red.TopFrontSide

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.

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Orthographic View SelectionFinding 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 SelectionSteps 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 viewsMost contours.Longest side.Least hidden lines.Best natural position.

Orthographic View Selection

Longest DimensionMost natural position.No hidden lines.Best shape description.

Orthographic View Selection NumbersAnother 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

Two views will be identicalAll 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.

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Two View Selection

Symmetrical parts. A third view would be identical to the other views

Second view is necessary fordepth.

Precedence of LinesIn 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

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REFERENCES

ReferencesMadsen, 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.

ReferencesSpencer, 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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