- Understanding Solid Objects
- Understanding Sketching Techniques
- 3.1 Technique of Lines
- 3.2 Sketching Straight Lines
- 3.3 Sketching Circles, Arcs, and Ellipses
- 3.4 Maintaining Proportions
- 3.5 One-View Drawings
- 3.6 Pictorial Sketching
- 3.7 Projection Methods
- 3.8 Axonometric Projection
- 3.9 Isometric Projection
- 3.10 Isometric Drawings
- 3.11 Making an Isometric Drawing
- 3.12 Offset Location Measurements
- 3.13 Hidden Lines and Centerlines
- 3.14 Angles in Isometric
- 3.15 Irregular Objects
- 3.16 Curves in Isometric
- 3.17 True Ellipses in Isometric
- 3.18 Orienting Ellipses in Isometric Drawings
- 3.19 Drawing Isometric Cylinders
- 3.20 Screw Threads in Isometric
- 3.21 Arcs in Isometric
- 3.22 spheres in Isometric
- 3.23 Oblique Sketches
- 3.24 Length of Receding Lines
- 3.25 Choice of Position in Oblique Drawings
- 3.26 Ellipses for Oblique Drawings
- 3.27 Angles in Oblique Projection
- 3.28 Sketching Assemblies
- 3.29 Sketching Perspectives
- 3.30 Curves and Circles in Perspective
- 3.31 Shading
- 3.32 Computer Graphics
- 3.33 Drawing on Drawing
- Key Words
- Chapter Summary
- Worksheets
- Review Questions
- Sketching Exercises
This chapter is from the book
This chapter is from the book
This chapter is from the book
3.33 Drawing on Drawing
Because CAD helps people produce accurate drawings that are easy to alter, store, and repurpose, computer automation has made the painstaking aspects of hand-rendering technical drawings nearly obsolete. Still, the ability to sketch with clarity is an immediate and universal way to record and communicate ideas.
The ability to think of complex objects in terms of their basic solid components and to identify relationships between various surfaces, edges, and vertices is basic to creating both hand-drawn (Figure 3.79) and computer-generated technical drawings. By understanding how to represent objects accurately, you can communicate efficiently as part of a team and increase your constructive visualization ability, or your ability to “think around corners.”
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3.79 Hand Sketch Conveying Custom Workstation Furniture Concept (Courtesy of Jacob A. Baron-Taltre.)
CAD at WORK: SKETCHING AND PARAMETRIC MODELING
The Design Process
The parametric modeling process in many ways mirrors the design process. Parametric CAD software lets you specify geometry, dimensions, and other essential parameters that control the model. To get the rough ideas down, the designer starts by making hand sketches. Then as the ideas are refined, more accurate drawings are created either with instruments or using CAD. Necessary analysis is performed and, in response, the design may change. The drawings are revised as needed to meet the new requirements. Eventually the drawings are approved so that the parts may be manufactured.
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A Rough Sketch in Pro/ENGINEER Sketcher
Rough Sketches
Using parametric modeling software, the designer first roughly sketches the basic shapes on the computer screen as though sketching freehand. These sketches do not need to have perfectly straight lines or accurate corners. The software interprets the sketch much as you would interpret a rough sketch given to you by a colleague. If the lines are nearly horizontal or vertical, the software assumes that you meant them to be so. If the line appears to be perpendicular, the software assumes that it is.
Constraining the Sketch
Using a parametric CAD system, you next refine the two-dimensional sketch by adding geometric constraints, which tell how to interpret the sketch, and by adding parametric dimensions, which control the size of sketch geometry. Once the sketch is refined, you can create it as a 3D feature to which other features can be added. As the design changes, you can change the dimensions and constraints that control the sketch geometry, and the parametric model will be updated to reflect the new design.
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A Constrained Sketch
When you are creating sketches by hand or for parametric modeling, think about the implications of the geometry you are drawing. Does the sketch imply that lines are perpendicular? Are the arcs that you have drawn intended to be tangent or intersecting? When you create a parametric model, the software applies rules to constrain the geometry, based on your sketch. You can remove, change, or add new constraints, but to use the software effectively you need to accurately depict the geometry you want formed.
CAD at WORK: PERSPECTIVE VIEWS IN AUTOCAD
AutoCAD software provides options for parallel and perspective viewing. You can use the menu for the ViewCube to quickly select Parallel or Perspective viewing options (Figure A). The defaults for perspective viewing determine the basic appearance when you select the perspective view types. Notice that the grid squares in the figure appear larger closer to the view and smaller when they are farther away. When parallel projection is selected, the grid lines remain parallel.
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(A) A Perspective View Created Using the DView Command in AutoCAD (Autodesk screen shots reprinted courtesy of Autodesk, Inc.)
An interactive command, Dview (dynamic viewing), lets you show 3D models and drawings in perspective (or parallel view) and interactively change the viewing options. Dview uses a camera and target analogy to create perspective views. Using the Camera option, you select a camera position (similar to the station point) with respect to the target point at which the camera is aimed. The Dview Distance option lets you change the distance between the camera and the object and calculate a new view. The Off option of the command turns perspective viewing off to return to a parallel view.
Specifying a distance that is too close can fill up the entire view with the object, in the same way that a close-up shot with a camera does.
The Zoom option of the Dview command acts like a normal zoom command when perspective viewing is off. When perspective viewing is on, you can zoom dynamically by moving the slider bar shown in Figure B to adjust the camera lens to change the field of view. The default is to show the view similar to what you would see through a camera with a 50 mm lens. During the Zoom option, moving the slider is similar to choosing the focal length for a camera lens, which changes the relative perspective appearance (Figure B). Shorter focal lengths exaggerate the perspective effect of closer features.
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(B) Using the Zoom Slider to Adjust Field of View (Autodesk screen shots reprinted courtesy of Autodesk, Inc.)
INDUSTRY CASE: SKETCHING FOR IDEATION: A CROSSACTION BREAKTHROUGH
When Oral-B hired LUNAR to create an innovative approach to brushing (and a new flagship product), they had no preconceived notions of what that would mean. But they knew that they wanted a brush that was ergonomically superior to the traditional “flat stick” design, and they wanted the brush to improve brushing effectiveness. The development of the Oral-B CrossAction Toothbrush is an example of the power of ideation in product design.
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Jeff Salazar, lead designer for the project, started first not with sketches but with extensive research into the kinesiology of brushing teeth. A research firm had been hired to do a study of how people hold their toothbrushes as they brush. They found that there are five basic grips. Each person might use more than one depending on the part of the mouth to be brushed. Two or three grips were the ones used by most people.
As the kinesiology study was underway the design team at LUNAR undertook their own study of brushing. Given that the design constraints were focused almost totally on ergonomics, they studied how people brush. They engaged team members and others and watched them brush. They used models of teeth to investigate brushing. They bought “flat stick” toothbrushes, heated them so they could be bent at different angles, and had a variety of people report back on their brushing experience with handles of different shapes. People of various sizes and backgrounds, male and female, were asked to brush with the angled handles. This helped them understand the extremes of the angles forward and back that the handle could form.
They also studied the competition. A competitor had come out with what it promised was a superior toothbrush—one that was “bent like a dental instrument.” After trying the toothbrush, however, the team concluded that the shape was only superior if someone else (e.g., the dental hygienist) was brushing your teeth. This key insight helped them focus the next stage of ideation on shapes with potential.
After discussing their results, the team selected five to six angle configurations for further study. The ergonomic results of the team’s efforts were an instinct that people wanted a toothbrush that would “fill the hand” more than the thin stick. But where should the brush be thicker? The team created a matrix that paired each of the angle configurations with the range of options for the handles’ thickness (Figure 3.80). Then, Jeff began sketching all the various combinations (see Figure 3.81).
3.80 The Matrix Used to Drive Concept Generation
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3.81 Sketches and Notes on the Concept as It Was Developed
After about a week of generating pencil sketches, Jeff decided he needed to “sketch” in 3D. Starting with a full-size sketch (Figure 3.82), he used a band saw to cut the shape of the sketch in foam, then shaped the foam into a model that he and others could hold and evaluate for various grips (Figure 3.83). Those that didn’t work for one grip or another were eliminated. The LUNAR team and their counterparts at Oral-B reviewed the various options and selected four for further development.
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3.82 Full-Size Sketches Used to Create the Foam “3D Sketches”
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3.83 Foam Models Used as 3D Sketches
At this point, the team created 3D models of the four candidates. Oral-B had prototypes made from the CAD models for the handles (Figure 3.84), added bristles, and embarked on consumer research that would drive the next stage of refinement. Consumers were asked to brush for one month, then attend a focus group to report on their experience. LUNAR Design was present to hear consumer reactions.
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3.84 Prototypes Generated from the 3D Model
What they found was that consumers loved the fatter handle. Its shape in the hand gave them more control when moving the brush to different parts of their mouth. The form provided optimal ergonomics for each of the five common grips. The faceted surface on the handle gave users a tactile clue as to where to place their fingers when gripping. The rubber-like material used for the facets was located where users exerted the most finger pressure—and it made it easier to hold the brush when wet. The very positive response indicated that the ergonomic handle could make a significant difference in brushing that consumers would appreciate. People reported that they loved their toothbrush now!
At the same time, Jeff and the LUNAR and Oral-B teams had to listen and interpret what they heard. Focus groups are a wealth of different reactions, and it is up to the team to determine what is relevant and what is peripheral. For example, one reaction was that the fatter handle did not fit in the standard toothbrush holder. The team had to assess whether this was an issue that would hamper acceptance of the toothbrush or whether the improved brushing experience would outweigh its importance to the customer.
The refinement of the design proceeded through two more prototypes (and additional ideation around packaging; see Figure 3.85) before the final Oral-B CrossAction was launched. The intensity of the ideation stage—and the many techniques used to generate and evaluate design ideas—were critical to the team’s success in achieving this breakthrough in brushing.
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3.85 Ideation Sketches for CrossAction Packaging
(All images courtesy of LUNAR.)
SKETCHING AT WORK
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Sketch for a Composting Latrine. The student chapter of Engineers Without Borders at Montana State University is collaborating with 57 schools in the Khwisero Division of southwestern Kenya to provide sustainable sanitary improvements including wells and composting latrines. (Sketch courtesy of Andrea Orr, Engineers Without Borders, MSU.)
Andrea Orr was a student in environment design at Montana State University and a co-fundraiser and co-project designer in the MSU chapter of Engineers Without Borders.
She created the sketch above during the building of a composting latrine that she and Chris Allen designed for a school in the Khwisero Division of southwestern Kenya. The sketch showed instructors and local government officials how the latrine would work.
Though they had done multiple sketches ahead of time, she and Allen did this sketch to clarify their ideas into one concept.
Orr did the sketch outdoors, sitting next to the school building. There was no computer available, because at the remote location, electricity was rarely available. She also did a drawing explaining how to use and maintain the latrine, which was posted inside the finished structure.
Orr said that when she is not working in the field, she still sketches by hand before transferring to CAD.
“There’s little bit of vagueness in a hand-drawn sketch that keeps it open to creativity,” said Orr.
“If you show a sketch to someone they are more likely to offer input and ideas than if it looks like a finished CAD rendering. That’s one of the reasons I don’t work in CAD until quite a few revisions into the project.”