Purpose Techniques Size and Proportion Alphabet of Lines Projections References Contents Click Shape to go to section.
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.
Practice Practice Practice Practice Practice Practice Practice Practice 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. 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 Size requirements. Shows design details Title Initialed and dated.
Sketching Techniques • Line Types: Inclined Line Vertical Line Horizontal Line
Run = 4 Rise = 2 Sketching Techniques • Finding the slope angle of an inclined line: Equation: 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.
Sketching Techniques • Sketching a Line.
Sketching Techniques • Sketching an Arc
Sketching Techniques • Sketching an Arc
1) Setup the diameter 2) Square in the diameter 3) Sketch diagonals Sketching Techniques • Sketching a Circle
4) Identify triangle centers 5) Sketch arcs Sketching Techniques • Sketching a Circle
Sketching Techniques • Precision Measurement • Refer to Presentation in Principles of Engineering
SIZE AND PROPORTION Contents
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.
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
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.
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 proportion.
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 size.
ALPAHBET OF LINES Contents
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.
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 here?
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 position. How many lines from the previous 2 slides can you identify here?
Pictorial • Pictorial sketches are sketches that show height, width, and depth all in one view. There are three common types: • Isometric • Oblique • Perspective
Width and depth lines are drawn at 30 degrees from the horizon line. Isometric Note one view shows height width and depth.
Oblique Front view is true size and shape. Width lines are parallel with the horizon. 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 pictorials to draw. Depth lines are drawn at an angle with the horizon.
Width lines are parallel with the horizon. In Cabinet Oblique depth is half size. This allows the view to look more realistic. Front view is true size and shape. Oblique
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 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 demonstration.
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 • 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
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 jump between this view and the ortho view on the next page. ORTHO
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. 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. Click to go back to ISO view. ISO
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.
In 3rd angle projection, the projection planes used to create views are as shown in red. Top Front Right Side Orthographic Spacial Quadrants and Planes This sketch shows the quadrants where the angles of projection are made from
Orthographic 3rd Angle Projection Views are projected onto planes that exist on the face of that view. Arrows show the direction of the projection ISO Symbol Back
Side Top In 1st angle projection the projection planes used to create the views are as shown in red. Front Orthographic Spacial Quadrants and Planes
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 Back
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 Most natural position. Longest Dimension Best shape description. No hidden lines.