TED 105: Communicating Technical Designs Sketching and Shape Description –Straight Lines...
-
Upload
bertha-underwood -
Category
Documents
-
view
221 -
download
0
Transcript of TED 105: Communicating Technical Designs Sketching and Shape Description –Straight Lines...
TED 105: Communicating Technical Designs
• Sketching and Shape Description– Straight Lines– Circles and Arcs– Proportions– Generating Technical Designs
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.
Freehand Sketching
• Most original designs are first expressed on medium as a freehand sketch.
• Used for:– Amplifying and clarifying– Recording
verbal explanations
Technical Sketching
• Engineers’ view: ability to render serviceable sketches greater value than skill to create instrument drawings
• Freehand sketch should not mean crude and sloppy
• Freehand sketch should be made with care and attention to proportion, clarity, and line widths.
Types of Sketches
Scale
• Typically not made to any scale.• Correct proportions are needed.• Size of sketch:
– Optional– Determined by:
• Complexity of object• Size of paper
• Small objects may be enlarged to show details clearly.
Do you want to be a good sketcher?
Purpose
• Proper documentation in a notebook is essential. When proper documentation is made, ideas are not lost and projects can be duplicated. The sketch on the next slide 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 requirements.
Initialed and dated.
Title
Sketching Techniques
• Line Types:
Vertical Line
Horizontal Line
Inclined Line
Sketching Techniques
• Finding the slope angle of an inclined line:
Run = 4Rise = 2
27sNote: 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:
tanss = RISE/RUN
tanss = 2/4
tanss = .5
s 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 thediameter
3) Sketch diagonals
Sketching Techniques
• Sketching a Circle
4) Identify trianglecenters
5) Sketch arcs
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 dimensions
are in windows.
You should also notice that
the use of graph paper also
helps in creating proper size
and 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
Alphabet of Lines
Alphabet of Lines
Object Line: Thick lines about .6mm(.032in) that show the visible edges of an object.
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.
Construction Line: Very lightly drawn lines used as guides to help draw
all other lines and shapes properly. Usually erased after being used.
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. (See
example of Long Break Lineon the next slide.)
Section Lines: Lines are used todefine where there is material
after a part of the object is cut away.
Alphabet of 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.
Long Break Lines: Break lines are usedto either show detail or as in this case they can
be 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.
Dimension Lines: Lines that are used toshow 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.
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 the
part as to not get confused with the object lines
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 comesoff 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 here?
Alphabet of linesPhantom 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 move45 degrees from it’s horizontal
position.
How many lines from the previous 2 slides can you
identify here?
PROJECTIONS•Pictorial
•Isometric
•Oblique
•Caviler
•Cabinet
•Perspective
•Orothographic
Pictorial
• Pictorial sketches are sketches that show height, width, and depth all in one view. There are three common types:– Isometric– Oblique – Perspective
Isometric
Note one view shows height width and depth.Width and depth lines
are drawn at 30 degrees from the horizon line.
Oblique
Front view is truesize and shape.Width lines are
parallel with the horizon.
Depth in an obliquepictorial is distorted.
Easiest of the pictorialsto draw.
In Cavalier Oblique depthis full size. This cube
has the same height, widthand depth dimensions
Depth lines are drawnat an angle with the
horizon.
Oblique
Front view is truesize and shape.
Width lines areparallel with the
horizon.In Cabinet Oblique depth
is half size. This allows the viewto 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
All lines in the depth projectto one point (vanishing
point). The location of the vanishing point is based
on your line of sight.
Note: The vanishingpoint in this sample is chosen for demonstration.
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)
ORTHO
The arrows represent the line of sight associated
with each view.
Use the button below to jumpbetween this
view and the orthoview on the next
page.
Orthographic Principal Views
ISO
Click to go backto ISO view.
Front, 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.
Note how the viewsare oriented. Each view is
adjacent to the other asif they were unfolded
from a 3D shape.
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 used
to create views areas 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
Back
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 areas shown in red.
Top
Front
Side
Orthographic 1st Angle Projection
Back
ISO Symbol
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.
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 DimensionMost 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 Selection
Uniform shape.
Two views will be identical
All dimensions easilyshown on one view.
One View Selection
It is also possible tohave one view drawingsof objects that are flat
and have even thickness.Gauges and gaskets aretwo 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 fordepth.
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
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.
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.
References
• Project Lead the Way. www.myteacherpages.com/webpages/IED/files/ Sketching.ppt
• 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.
References
• Johnson, Cindy M., Lockhart, Shawna D., Engineering Design Communication, Prentice Hall, 2000, ISBN 0-201-33151-9.
• 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.
Do you want to be a good sketcher?
First Slide