Technology

22

Competency FourCommunicate the design processes.

CONTENT

Objective 4.01

Explain terms and procedures involving measurement tools.

The following outline characterizes what should be taught under Objective 4.01

· Explain measurement terms

· Explain measurement tools

· List measurement prefixes (see appendix)

· Explain the customary and metric systems of measurement (see appendix)

· Explain measurement conversions and calculations (see appendix)

Click here to see a companion PowerPoint presentation.

The following benchmarks from the Standards for Technological Literacy address this objective:

Standard 9, Benchmarks H

Standard 12, Benchmarks L, P

Standard 17, Benchmarks Q

“Technological knowledge and processes are communicated using symbols, measurement, conventions, icons, graphic images, and languages that incorporate a variety of visual, auditory and tactile stimuli.”(R1)

Measurement is the process of determining the size, amount or extent of something. It objectively describes the physical qualities of an object. It is also the practice of comparing qualities of an object to a standard.

There are two measurement systems used in the world today, the U.S. Customary System and the Metric System (System International, SI). The United States is the only industrialized country that has not adopted the metric system for everyday use.

The U.S. Customary system uses unique units for each quality being measured. The lack of uniform multiples can make the system confusing. It is based on units of measurement established during the Middle Ages in Europe. The basic units of measure for length is the inch; for weight, the pound; for volume, the quart; and for temperature, degrees Fahrenheit.

The Metric system was established in France. The basic unit of measure for length is the meter; for weight, gram; for volume, the liter; and for temperature, degrees Celsius.

Metric Prefixes – The metric system is based on ten. “ There is a logical progression from smaller units to larger ones, since all sizes of units are based on ten.”(p. 119, R3) The metric system starts with a base unit. Smaller units are decimal fractions of the base unit. Larger units are multiples of ten. The metric system uses a prefix to show us how the base unit has been changed. For example, the unit for distance is the meter. For large distances, the kilometer is used. The prefix kilo means 1000, so seven kilometers is equal to 7000 meters. For small distances, the millimeter is used. The prefix milli means 1/1000th. Twelve millimeters are 12/1000 of a meter. The metric system lends itself to easy use in mathematical formulas. The metric system uses the same prefixes for all base units.

Measurement Tools

Click here to see a companion PowerPoint presentation.

Before a technician can measure anything using the customary or metric systems, they must first be able to explain how to use the appropriate measuring tools. Some measuring tools commonly used by technicians in their work include: rules, calipers, micrometers, squares, protractors, various gauges, weight scales, and calibrated containers.

Rules are used to measure length, width and thickness. Some rules used include: standard 12 inch rule, mechanical rule, drafter’s rule, machinist’s rule, metric rule, yard stick, meter stick, and tape measure. Rules are calibrated in many different ways. Technicians must be able to interpret calibrations when using rules.

Calipers are used to measure diameters on either the inside or outside of an object. The two types of calipers are the outside caliper and the inside caliper. Calipers may need to be used in conjunction with a rule to determine the value of a measurement. Many calipers are adjusted by turning it’s thumb screw until the legs fit snugly against the surface being measured. The distance between the legs is then measured with a rule.

Micrometers are very precise tools for measuring the length, thickness or diameter of small objects. A micrometer that uses customary units can measure to one thousandths (0.001) of an inch. A metric micrometer can measure to one hundredth (0.01) of a millimeter.

Squares are used to measure or lay out perpendicular lines (lines at 90 degree angles). Four commonly used squares are the try square, framing square, combination square, and center square. A combination square can also measure 45 degree angles.

Protractors are used to measure angles from 0 to 180 degrees for protractors that are half-moon shaped and 0 to 360 degrees for circular shaped protractors. Many protractors can also be used to measure length along their straight edge.

3.00

1.00

2.00

3.00

1.00

2.00

Weight scales measure weight or mass. Scales can range from the common bathroom scale to the most sensitive scientific scale. Scales can be analog or digital, manual or electronic. As you see, there are many factors to consider when selecting a scale.

Calibrated containers are used to measure volume. Cooks use calibrated containers to measure ingredients for recipes. Scientists use calibrated containers in the science lab. Measuring spoons, measuring cups, and lab beakers are three types of calibrated containers (R3, 117-129).

See Appendix on Measurement for more required information.

Click here to see the Measurement Appendix.

Related VoCATS Test Items (includes contents of Measurement Appendix)

1. What is the basic unit of measurement for length in the Metric (SI) System?

A. liter

B. gram

C. inch

D. meter

2. Which of the following best describes the definition of measurement?

A. the process of determining the size, amount, or extent of something

B. using a measurement device

C. the process of converting from US Customary to SI (metric) system

D. the study of the SI (metric) and US Customary systems

3. The practice of comparing qualities of an object to a standard is

A. (SI)Metric System

B. comparison

C. quality control

D. measurement

4. Convert the miles traveled across a bridge spanning a distance of 10560 feet?

A. 2 miles

B. 1.5 miles

C. 3 miles

D. 4 miles

5. Which of the following tools is needed to measure objects in very precise increments, thousandths (0.001) of an inch?

A. caliper

B. micrometer

C. protractor

D. rule

6. What measurement tool would be used for laying out perpendicular lines?

A. protractor

B. caliper

C. square

D. rule

7. When measuring units of volume, scientists utilize:

A. calibrated containers

B. calipers

C. micrometers

D. scales

8. When measuring angles from 00 to 1800, the proper tool would be a:

A. caliper

B. micrometer

C. protractor

D. combination square

9. Horsepower and watts are a measurement of:

A. area

B. speed

C. power

D. pressure

10. Which unit of measurement is used for calculating area?

A. square feet

B. cubic centimeters

C. square liters

D. cubic liters

11. What is the measurement for temperature in the SI (metric) system?

A. kilograms

B. Fahrenheit

C. Celsius

D. volume

12. The freezing and boiling point of water in the US Customary System is:

A. 00 to 1800

B. 320 to 2120

C. 00 to 1000

D. 00 to 2120

13. Which of the following is the unit of measure of energy?

A. force

B. watts

C. BTU’s

D. pounds

14. Which unit of measure is used for both weight and volume in the US Customary?

A. pounds

B. feet

C. ounces

D. cups

15. Which of the following is the appropriate term for the absolute Fahrenheit scale?

A. Rankine

B. Celsius

C. Kelvin

D. metric

16. Which of the following best describes the function of a rule?

A. It is a straight edge used for marking lines

B. It is used to measure diameter

C. It is used to measure length, width, and thickness

D. It is used to measure angles

17. Joules and calories are used in the measurement of:

A. pressure

B. speed

C. energy

D. torque

18. The calibrated container is used to measure:

A. volume

B. mass

C. weight

D. diameter

19. What are the two measurement systems used in the world today?

A. Customary and SI

B. SI and metric

C. American and European

D. Customary and American

20. Instruments that are used to measure mass are:

A. calipers

B. weight scale

C. digital

D. micrometer

21. Measuring to precise, exact increments is referred to as:

A. linear measurement

B. indirect measurement

C. precision measurement

D. standard measurement

22. The most common linear measurement device is the:

A. rule

B. square

C. measuring tape

D. yardstick

23. Sensors gathering measurements and then displaying them on an output device is an example of:

A. indirect reading measurement

B. computer output

C. precision measurement

D. CAD

Objective 4.02

Students will apply measuring techniques.

The measurement of part and product size is important in technological design and production activities. Generally this type of measurement can be divided into two levels of accuracy, Standard Measurement and Precision measurement. (R3)

Standard Measurement

Many production settings do not require close measurements. The length of a house, the width of a playing field need not be very accurate. If the product is within a fraction of an inch it will work fine. These measurements are often given to the foot, inch or fraction of an inch in the customary system, or the nearest whole millimeter in the metric system.

The material being measured is also important. For example, wood changes (expands or shrinks) in size with changes in moisture content and the atmospheric humidity. Measurements closer than 1/32 in. or 1mm are not useful. Wood can change more than that in one day.

Standard measurements are common in cabinet and furniture manufacturing plants, construction industries, and printing companies. The printing industry uses its own system based on the pica (1/6in.) and the point (1/72in.)

Precision Measurement

Standard measurement is not accurate enough for many production applications. Watch parts and engine pistons would be useless if they varied by as much a 1/32in. (0.8mm).

These parts must be manufactured to an accurate size. For this type of production, precision measurement is required. Measurements of 1/1000 in. to 1/10,000 in. are precise in the customary system. Metric precision measurement will measure to within 0.01mm (one one-hundredth of a millimeter).

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2.0000

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.7500

.3750

.7500

.1250

.1250

2.0000

2.0000

.3750 .7500 .3750

.7500

.1250

.1250

Direct Reading Measurement Tools

Three common uses of measurement are finding linear dimensions, diameters, and angles. Each of these three features can be measured using standard precision devices.

Linear Measurement

The most common linear measurement device is the rule. The most common divisions are sixteenths (1/16 in.) Metric rules are divided in whole millimeters. The part is measured with a rule by aligning one end of the part with the end of the rule or with an inch mark. The linear measurement is taken by reading the rule division at the other end of the part.

Flexible rules are often called tape rules. They are used in woodworking and carpentry applications. There is a hook at one end of the rule that is hooked to the end of the board or structure. The tape is pulled out until it reaches the other end of the board or structure. A measurement is then taken.

Measuring Diameters

A common measurement task involves determining the diameter of round material or parts. Precise diameters can be measured by placing a part between the anvil and the spindle of a micrometer and reading the measurement on the barrel.

Measuring Angles

The angle between two adjacent surfaces is important in many situations. The legs of a desk are generally square (at a 90(angle) with the top. Squares are used to mark angles. The head is placed against one surface of the material. The blade is allowed to rest on an adjacent surface. If the blade touches the surface over its entire length, the part is square (R3, 124-125).

Indirect Reading Measurement Tools

In many modern measuring systems, humans no longer take measurements. Sensors gather the measurement data, which is processed by computers or other automatic devices. The final measurement can be displayed on an output device such as a digital read-out, computer screen, or printout. These new systems include laser measuring devices, optical comparators, and direct reading thermometers.

You may measure length, weight, temperature, or other qualities. However, there must be a reason for doing the measuring. All technological processes produce products or services.

These may be goods, buildings, or communication media.

Measurement is necessary in designing most anything. Its size, shape, or other properties are communicated through measurements. Processing equipment is set up and operated using these design measurements. Materials needed to construct the item are ordered using measurement systems. All personal or industrial production is based on measurement systems.

Measurement can also be used to compare the present condition with a desired condition. The process of setting standards, measuring features, comparing them to standards, and making corrective actions is called quality control. The foundation of a quality control system is measurement and analysis.

Measurement describes distance, mass, time, temperature, number of particles, electrical current, and light intensity. It involves comparing a physical characteristic to an established standard. The common standards are the metric system and the U.S. customary system. These systems allow people to communicate designs, order materials, set up machines, fabricate products, and control quality. (R3)

Incorporate measurement into a variety of activities, however, as a guided practice students could:

· Measure three dimensional items around the lab.

· Measure machined steel with micrometers.

· Use a scale to determine the weights of items of equal volume but varying density.

· Use a thermometer to determine comfort zones around the school building.

· Use a light meter to determine areas of inadequate lighting around the school building.

· Use an architect’s scale to lay out scale models.

· Use a tri-square to lay out perpendicular lines, etc.

· Have students apply a tolerance of plus or minus (() 1/16 inch to linear measurements.

Using the instructions provided by your teacher, choose the appropriate tools and make measurements. Convert all measurements as directed by the teacher, then verify conversions using the appropriate tools.

Students should be evaluated on the following criteria:

1. Measurement Accuracy

0-50 points

2. Conversion Accuracy

0-50 points

Objective 4.03

Explain terms and procedures utilized in technical sketching

The following outline characterizes what should be taught under Objective 4.03

· Explain orthographic sketches and pictorial sketches

· Explain rough, refined, and detail sketches

· Explain types of lines used in sketching and drafting

The following benchmarks from the Standards for Technological Literacy address this objective:

(R1) Standard 17, Benchmarks J, K pg. 171.

DRAFTING: THE UNIVERSAL LANGUAGE

Drafting is the process of accurately representing three-dimensional objects and structures on a two-dimensional surface, usually paper. It is an accurate drawing process used for nearly every product or structure made today – large or small.

Integrated circuits, shoes, tools, cars, bridges, and skyscrapers are just a few examples of things that are drafted. Drawings are also used to communicate ideas effectively and accurately.

Sketching

Once the designer has conceived a number of ideas, the ideas must be recorded. The most common recording method is to develop rough sketches of the products, structures, or system components. The term “rough” is not used to describe the quality of the drawing. They often represent good sketching techniques. The term rough describes the state of the design ideas. It suggests that the designs are incomplete and unrefined. Refining original designs is the second step in developing a design solution. Refined design ideas may also be developed by merging ideas from two or more rough sketches into a refined sketch. The new idea may not look anything like the original rough sketches. The rough sketch and refined sketch communicate shape and proportion. They do not communicate size. For this task, a third type of sketch is needed, called a detailed sketch. It communicates the information needed to build a model of the product or structure. Building requires three major types of information: size information explains the overall dimensions of the object, or the size of the features on an object; location information gives the position of the features within the object; and geometry information describes the geometric shape or relationship of features on the object.

Developing Pictorial Sketches

Designers often use pictorial sketching techniques to capture and further refine product design ideas. These techniques try to show the artifact much like the human eye would see it. Therefore, a single view is used to show how the front, sides, and top would appear. (R3)

Three basic techniques are used to develop pictorial sketches:

Oblique sketches

Oblique sketches are the easiest pictorial sketches to produce. They show the front view as if a person was looking directly at it. The sides and top extend back from the front view. They are shown with parallel lines that are generally drawn at 45( to the front view. The two types of oblique drawings are cavalier and cabinet. The cavalier oblique drawing causes the sides and top to look deeper than they are. To compensate for this appearance cabinet oblique drawings are often used. This type of drawing shortens the lines that project back from the front to one-half their original length.

Isometric Sketches

Isometric sketches are the second type of pictorial drawings used to produce refined sketches. The word isometric means equal measure. Isometric sketches get their name because the angles formed by the lines at the upper right corner are equal – each is 120(. The object is shown as if it were viewed from one corner.

Perspective Sketches

Perspective sketches show the object as the human eye or camera would see it. This realism is obtained by having parallel lines meet at a distant vantage point. Developing the perspective view is more difficult to draw than oblique or isometric views. However, perspectives are the most realistic of the three sketches.

Types of Perspective Views

There are three major types of perspective views: one-point, two-point, and three-point. One-point perspective shows an object as if you were directly in front of it. Two-point perspective shows how an object would appear if you stood at one corner. A three-point perspective shows how the eye sees the length, width, and height of an object. All lines in this drawing extend toward a vanishing point. Changing the position of the horizon line can cause the object to be seen as if the observer were looking down on the object

(aerial view), directly at it (general view), or up at it (ground view).

Detail Drawings

Most detail drawings are prepared using the multi-view method. This drawing method places one or more views of the object in one drawing. The number of views will depend on how complex the part is. Generally, a top, right side, and front view are shown. Multi-view drawings use orthographic projection to project information at right angles to new views. The surface with the most detail is chosen to be shown in the front view. The front view is drawn in the lower left quadrant of the paper. Projection lines are extended to the top and right of the front view to form the top and side views (orthographic projection).

Drawing Lines

One set of drafting standards deals with lines and line weights. The shape of the object is of primary importance. The lines that outline the object and its major details must stand out. These solid lines are called object lines and are the darkest on all drawings. Some details are hidden in one or more views. Therefore, they are shown but with lighter, dashed lines called hidden lines. A third type of line locates holes and arcs on a part. These lines pass through the center of the hole and are thus called center lines. The size and the shape of an object are communicated by detail drawings. These are constructed of a series of light long and short dashes. Dimensioning uses two kinds of lines. First, the extension lines indicate the points from which the measurements are taken. Between the extension lines are dimension lines. These have arrows (or other terminators) pointing to the extension lines that indicate the range of the dimension. The dimension and extension lines are the same weight as hidden lines (R1, 104-105; R2, 162-166; R3, 164-168).

Click here to view a PowerPoint presentation on technical sketching.

Related VoCATS Test Items

1. What type of sketch shows the front view as if a person were looking directly at it?

A. rough

B. refined

C. detail

D. oblique

2. A pictorial sketch that has been drawn as if it were viewed from one corner is known as:

A. perspective

B. isometric

C. detailed

D. orthographic

3. A sketch that shows the object as the human eye or camera would see it is known as:

A. perspective

B. orthographic

C. isometric

D. three-view

4. A multi-view drawing that typically shows the front view, right side view, and top view is called:

A. perspective

B. orthographic

C. isometric

D. oblique

5. A HIDDEN line looks like:

B.

C.

D.

6. A CENTER LINE looks like:

A.

B.

C.

D.

7. A VISIBLE line (Object line) most nearly looks like:

A.

B

C

D

8. Which of the following symbols represents the word PERPENDICULAR?

A

B

C

D

9. The FRONT view consists of:

A.Depth and Height.

B.Width and Depth.

C.Height and Circumference.

D.Width and Height.

10. In an orthographic sketch, the side view is perfectly in line with the front view. What is this called?

A. projection

B. construction

C. isometric

D. oblique

11. For orthographic drawing, the surface of the object with the most detail is shown in which view?

A. sectional

B. side

C. top

D. front

12. Most detail drawings are what type of drawing?

A. perspective

B. orthographic

C. isometric

D. oblique

13. In orthographic drawing, the top view's width dimension is projected from what other view?

A. side

B. bottom

C. front

D. auxiliary

14. This type of drawing shortens the lines that project from front to back one-half their original length is:

A. oblique

B. cabinet

C. cavalier

D. orthographic

Objective 4.04

Apply technical sketching utilizing orthographic and pictorial layout

When students begin to implement any of their solutions, they should develop a detailed orthographic, a pictorial, and perhaps assembly sketches as seen on the right. These applications of sketching should be included with the criteria related to whatever unit you have integrated sketching and design into.

Various applications may include the following TSA competitive events:

· Technical Sketching

· Flight Endurance

· Structural Systems

· Graphic Design

· Dragster Design

· Transportation Modeling

· Architectural Model

· Manufacturing Prototype

· National Engineering Design Challenge

Return to TLP 1

HYPERLINK \l "to404tlp5"

Return to TLP 5

Produce the following types of sketches: thumbnail, oblique, isometric, and orthographic.

Evaluation is based on the following criteria:

1. Accuracy of measurement or proportion

0-25 points

2. Accurate presentation of views

0-25 points

3. Proper use of lines

0-25 points

4. Neatness of drawing

0-25 points

Go to Performance Rubric 4.04

Objective 4.05

Explain computer processes used in computerized 2D/3D modeling

The following outline characterizes what should be taught under Objective 4.05

· Describe the advantages of CAD

· Describe applications of CAD

· Describe CAD terminology

CAD/CADD

CAD (Computer-Aided Design) refers to a process that uses a computer and drawing software to assist the drafter in preparing mechanical or architectural drawings. CADD (Computer-Aided Design and Drafting) is closely related to CAD. CADD systems use extra functions that simulate testing products. Professional designers use CADD to increase the quality of their work.

Advantages of CAD - The heart of a CAD system is the computer. A computer is capable of producing drawings much faster than humans. Computers can be programmed to perform certain complex functions with just the push of a single key. A traditional drafter may have to complete dozens of pencil strokes to perform the same function. Computers are generally more accurate than humans, and they can perform the same function over and over without errors or deviations. CAD has several advantages over traditional drafting methods. Four advantages of CAD are: speed, quality, ease of modification, and cost.

Speed – using a CAD system, a drafter can produce more drawings in a given amount of time than by using traditional drafting methods. In traditional drafting, every drawing is created by moving a pencil. The traditional drafter must use several tools just to produce a line. Every line must be carefully planned to prevent mistakes. If a mistake is made, all incorrect lines must be thoroughly erased and redrawn. Sometimes, the entire drawing must be redrawn. Using CAD, many tasks are performed automatically. For instance to draw a line, the operator simply sets the end points for the line, and the system does the rest. No drawing board, T-square, triangle, scale or pencil is required. With CAD, repetitive tasks can be accomplished with just the push of a single key. Using the COPY command, the drafter can duplicate identical objects. Dimensions can be set on a CAD system more quickly than traditional methods, and many CAD programs have symbol libraries which contain commonly used symbols for a particular application. This eliminates the need to draw a symbol each time it is needed.

Quality – in addition to being quicker, CAD systems increase quality. The overall quality of a design is improved by increasing line quality, neatness, legibility, and accuracy. It is hard to achieve consistent line quality each time using traditional methods. Using CAD, the computer draws the same width line every time. With traditional methods, drawings become smeared and smudged as tools are moved across the paper. In CAD, the drawing is in the computer and is not put on paper until it is finished. When it is put on paper, it is

in ink. Every drafter draws and letters differently. Some are very neat, while some are not. The computer draws and letters the same regardless of the operator. This increases the overall legibility of drawings produced with CAD. Accuracy using traditional drafting methods may be to within one one-hundredth of an inch. In CAD, the accuracy could be better than one one-thousandths of an inch. All of these factors combine to increase the quality of drawings produced on a CAD system.

Ease of modification – it is common for a drafter to have a need to revise a drawing one or more times. Making modifications to a drawing is a time consuming task using traditional drafting methods. But, with CAD, it can be accomplished in much less time. CAD drawings are stored in memory and can be recalled and modified easily. Portions of a drawing can be deleted and replaced, or the operator can change existing lines and objects. Minor changes to traditional drawings can be far more complicated and time consuming than major changes made to a CAD drawing.

Cost – at first thought, CAD may seem more costly than traditional drafting methods. The cost of a CAD system can be great, and operators have to be trained. But, in the long run, using CAD can save money. All of the advantages listed above help make CAD more cost effective than traditional drafting.

2D-3D- The basic categories include 2D, 2.5D, and 3D. 3D programs store a three-dimensional database for each point of an object. The number of dimensions greatly affects the ability to view and display pictorial views of the object.

3D Functions- The 2D packages store data for the X and Y coordinates of all points. Packages which are 2.5D also store data points for the X and Y coordinates, but they also provide simplified 3D visualization for objects where thickness has been stored earlier. The 3D programs store data for the X, Y, and Z coordinates of each data point. They provide full 3D capabilities from the 3D database.

3D Systems - Stereo Lithography Apparatus (SLA) – produces full-size, 3D plastic models directly from CAD drawings. (R2 page 271 )

Applications of CAD

CAD is used in every drafting discipline. Mechanical engineering, architectural engineering, construction, and electrical engineering all use CAD to produce drawings of the trade. Mechanical drafters design products using multi-view drawings and models. Architects use CAD to design buildings and other structures. CAD helps electrical engineers and drafters design electrical and electronic products. Basically, a CAD system is useful to anyone who has a reason to draw.

The computer is the heart of the CAD system. Common computer components such as the CPU, monitor, keyboard, mouse, hard drive, floppy drive, and printer are all part of the standard CAD system. However, some additional hardware and software are required to make a CAD system functional. The software that makes the computer perform CAD functions is an essential part of any CAD system. Many CAD programs exist on the market. The basics to using most programs are the same. Most come with the users’ guides and tutorials to help operators learn to use the program. It is important to refer to these user aids when working with a new CAD system. Some hardware devices specifically associated with CAD systems are the digitizer pen and tablet, the function board, and the plotter. The first two are input devices, while the plotter is an output device.

As with many other things, Computer-Aided Design has a language of its own. Basically, all CAD systems are similar in their design and function. The main difference is the terms used to represent drawing commands. The terms presented here are common to most systems. You should consult the operator’s manual of any system before using it for the first time. Knowing the correct terminology can save you a lot of time and effort when working with a new system.

CAD Terminology

Commands- short words which, when entered, causes the computer to perform some function. Each instruction entered into the computer to create a line, circle or other graphic entity is a command.

Entity-an object or text item created using CAD software.

Grids-help the drafter easily locate position on the drawing. Grid patterns are normally dots on the screen. They are used like lines on graph paper. The dots are called grid dots. The grid dots assist the drafter in drawing entities. Most programs allow the drafter to adjust the spacing of the dots. This is referred to as grid spacing.

Snap Grids-or grid snaps is used to lock the drawing cursor to grid points as it is moved across the screen. When snap grid is on, the cursor jumps from grid point to grid point as it moves across the screen. With snap grid, the cursor can only be positioned at a grid point. Without snap grid, the cursor glides across the screen and can be positioned anywhere.

Rotation-used to rotate an entity around a base point. There are two options when using the rotate command. The entity can be rotated by specifying a specific angle of rotation, or it can be rotated by “grabbing on corner of the entity” (called a handle point) and dragging that point around the base point.

Zoom-allows the drafter to move in on a particular part of a drawing. By moving in on the drawing, the drafter can view more details. This function is extremely useful when working with very detailed drawings.

Windows- most CAD programs allow the screen to be split into separate windows. Each window is a separate display screen. The windows function is useful when working on very large drawings. It allows the drafter to work in different parts of the drawing that ware widely separated from each other. Another window function available with most CAD programs is the zoom window. This command allows enlargement of a section of the drawing by placing a window around it. It is a method of selecting a specific part of the drawing to enlarge (R2, 166-167; R3, 168-170).

Cartesian Coordinates System

Cartesian Coordinate System ‑ a method of graphical point location. All CAD systems use this system as a standard. It allows precise positioning of entities on the drawing surface.

Coordinate pair ‑ represents the position of a point. The first number represents the X coordinate while the second is the Y coordinate.

X,Y, Coordinate ‑ the X coordinate is the point's distance from the origin along the X axis. The Y coordinate is the point's distance from the origin along the Y axis. The origin is the intersection of the two axes. The intersection of the X and Y axes creates four quadrants for plotting points.

Check coordinates

Notice, X and Y points in quadrant I are positive. In quadrant 2, X is positive and Y is negative. In quadrant 3, both X and Y are negative, while in quadrant 4, X is negative and Y is positive.

Absolute Coordinates ‑ give the position measured from the origin of the drawing. Absolute coordinates refer to precise locations on the Cartesian coordinate grid. For example, coordinates of 4,2 defines a point four units to the right and two units above the origin.

Relative Coordinates ‑ refer to a point or location measured from a previous point. For example, coordinates could be specified for a second point that is at 8,4 from the original point 4,2. To plot this second point, you would move eight units to the right and four units above the point 4,2. The absolute coordinates for this second point would be 12,6.

Related VoCATS Test Items

1. The lines that outline the object and its major details must stand out. These solid lines are called:

A. hidden lines

B. dark lines

C. object lines

D. outline lines

2. The lines with arrows or other terminators at the ends which extend between extension lines are called:

A. dimension lines

B. center lines

C. cutting plane lines

D. section lines

3. The four advantages of CAD are speed, quality, ease of modification, and:

A. cartooning

B. cost reduction

C. sketching tool

D. developing rough layout

4. CAD stands for which one of the following?

A. computer-aided design

B. computer-aided dimensioning

C. computer-aided drawing

D. computer-aided decision making

5. A short word which, when entered, causes the computer to perform a function is called:

A. ditto

B. command

C. parameter

D. abbreviation

6. What drawings depict real life appearances, usually drawn to one or two-point vanishing points?

A. thumbnail

B. orthographic

C. oblique

D. perspective

7. Which of the following professionals would probably NOT use CAD in their work?

A. architect

B. mechanical drafter

C. electrical engineer

D. secretary

8. What method of graphic point location is used by all CAD systems as a standard?

A. four quadrant

B. Cartesian coordinate system

C. x-axis system

D. polar coordinate system

9. When utilizing the x, y, and z coordinates in 3 D modeling, the z axis represents:

A. horizontal axis

B. width axis

C. vertical axis

D. length axis

10. To move into a particular part of a drawing, the drafter would use the:

A. grid command

B. zoom command

C. rotate command

D. entity command

11. A collection of tool buttons grouped together is called a:

A. status line

B. menu bar

C. tool button

D. tool bar

12. Two dimensional design packages store data for the:

A. x, y, and z points

B. x points only

C. x and y points only

D. y points only

13. Three dimensional design packages store data for the:

A. x, y, and z points

B. coordinate pairs

C. axis points

D. outline forms

Objective 4.06

Utilize the computer as a design tool including 2D/3D modeling

When students begin to implement any of their solutions, they should develop a detailed orthographic, a pictorial, and perhaps assembly CAD drawings as seen below. These applications of sketching should be included with the criteria related to whatever unit you have integrated sketching and design into.

The Technology Student Association offers two competitive events that are related to this competency. Have your students use the TSA criteria in the development of their work. TSA Related Events:

· Computer-Aided Drafting and Design

· Technical Design and Sketching.

· Scientific and Technical Visualization

· Architectural Model

· Desktop Publishing

Using the design brief provided by your teacher, produce an orthographic and/or isometric drawing.

Evaluation is base on the following criteria:

1. Accuracy, presentation and completeness (all necessary measurements are given, views are correctly positioned and all required views are provided)

0-25 points

2. Technical complexity (full and appropriate use of CAD functions, software and hardware are evident)

0-25 points

3. Creative (quality, creative solutions are offered)

0-25 points

4. Effectiveness (drawing clear, precisely and economically conveys information to be communicated)

0-25 points

Go to Performance Rubric 4.06

Resources

R1 = Standards for

Technological Literacy, page 174

R2 = Technology Today and Tomorrow

R3 = Technology Systems, page 119

R4 = National TSA Curriculum Guide

R1 = Standards for Technological Literacy, page 174

R3 = Technology Systems, page 119

R3 = Technology Systems, page 121

R3 = Technology Systems, page 126