A computer workstation is where CAD drawings are produced. Basically, there are two main classifications of computers: mainframe and personal computers. Mainframe computers are used extensively by large corporations and governments for a variety of functions because of their speed and power. However, main­frames are extremely expensive and therefore are not effective and efficient solutions for smaller companies and organizations.

The personal computer has become the primary workhorse of the CAD community because of its size, cost of operation and maintenance, and speed.

Basically, a computer can be divided into two main categories: hardware and software. The hardware is made up of an assortment of electronic devices interconnected by electric cables, Figure 27.4. In short, hard­ware can be thought of as everything on a computer that can be physically touched. Software consists of the instructions used to make the computer’s hardware work. It enables the operator to control the computer.

CPU (CENTRAL PROCESSING UNIT) FIGURE 27.4 ■ Typical computer workstation.

HARDWARE COMPONENTS OF A CAD WORKSTATION

There are several key pieces of hardware that make up a CAD workstation. The first is the Central Processing Unit (CPU). The CPU is the heart of the computer; it controls the operation of the computer by performing arithmetic and logical operations and decodes and executes instructions provided by either the operator or a program. It is often commercially referred to as a tower or mini-tower.

Instructions from the user are entered into the computer using either a keyboard and/or a mouse. A key­board, similar to a typewriter, allows the user to enter data and commands into the computer by pressing keys. The mouse is also an input device that can be used to enter data and/or commands into a computer by allowing the user to select items on the screen.

The monitor, resembling a television screen, provides visual graphic output to the operator. Monitors, like television, are also available in different sizes and configurations. A monitor can be either monochrome (dis­playing only two colors) or color. Information can also be entered into a computer using a scanner. A scanner is a device that reads text and/or illustrations that were printed on paper and translates it into a form that the computer can understand. A scanner works by placing an imaginary grid onto the image and then determin­ing if the different areas of the grid are filled in or empty. While the scanner translates paper documents into a form the computer can understand, the printer takes information from the computer (text, illustrations, etc.) and prints them on paper. Although this is the minimal equipment necessary to produce a CAD drawing, other apparatus (peripheral devices) may also be incorporated into the workstation such as a stylus and plotter to produce large drawings.

CAD Software

CAD software is the most important component of the CAD workstation. Software by definition is anything that can be stored electronically. Typically, software is considered to be a program that controls and tells the computer to perform a specific function or set of functions. The output of a CAD program can be working and design drawings, technical data, piping, architectural and mechanical designs, or electrical and electronic circuitry. A variety of software programs are available for various purposes including auxiliary software to increase the efficiency of primary software. Examples of specific kinds of software are “AutoCAD,” “CADkey,” and “Microsotation.”

Typically, a CAD program will allow the user to enter information into the system either by selecting menu items or by typing commands. CAD menus are organized into categories such as geometric creations (lines, circles, arcs, etc.) and editing (erase, trim, extend, etc.). This enables the CAD operator to quickly select common and similar commands from a list, thus increasing the efficiency of creating a drawing. Examples of a CAD menu can be seen in Figure 27.5.

The selection of software items shown on the monitor screen is accomplished by using the cursor. A cursor is an indicator found on the screen that may be in the form of a small triangle, arrow, or some other similar configuration. Its purpose is to act as a pointer for selecting items on the screen for processing to the CPU. The cursor is moved by the operator by moving the mouse on the pad to select appropriate items for input to the CPU. Items may include lines, shapes, dimensions, and notes, as well as welding symbols.

To summarize, the computer operator uses a software program previously loaded onto the computer’s hard disc to create a drawing. The operator communicates to the CPU by means of a keyboard and mouse, selecting items from the menu shown on the monitor’s screen to formulate a drawing, notes, as well as weld­ing symbols. The completed drawing shown on the monitor’s screen is sent to the printer for printing. The resulting output by the printer is a working or design drawing printed on paper which is referred to as hard copy. Typical CAD drawings are shown in Figure 27.1, Figure 27.2, and Figure 27.3. Note the regularity of the line weight, the precise intersections of lines, and the consistency of dimension lettering. Also note that in Figure 27.2 dimensions are shown in decimal fractions rather than common fractions. This has become the preferred practice for dimensioning a variety of drawings.

In conclusion, CAD is an extremely useful tool in the design and manufacturing process. Its output increases production, standardizes drawings, and generates data and a variety of drawings that may be elec­tronically transferred to other computers.

Note: A glossary of computer terminology is found in Appendix 8.

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FIGURE 27.5 ■ Example of a CAD menu.

UNIT 27: REVIEW A

1. Describe the difference between CAD and CADD.

2. List three different CAD packages that are currently available on the market today.

3. What are two advantages of using CAD over conventional manual drafting practices?

4. What is the difference between hardware and software?

5. List two output devices and input devices used at a computer workstation.

a. Output device

(1)______________________________________

(2)

b. Input device

(1)______________________________________

(2)

6. How does a monitor differ from a printer?

7. Information can generally be input into a CAD package using what two methods?

8. Define the following terms:

a. CIM

b. CAM

9. In the following illustration, (a) identify each component of the CAD workstation and (b) describe its function.

UNIT 27: REVIEW B

The following problems refer to foldout drawing number 7, Die Stand Frame. Graph paper is provided at the end of this review for your use.

This die stand frame print is one that is actually used in industry. Some of the practices in dimensioning the prints and drawings of the views do not necessar­ily comply with standard dimensioning practices. In such cases, the company’s standards were applied.

NOTE #1: In many instances, extension lines touch object lines in the dimensioning parts of this drawing. This is not standard practice. As a result, it is difficult to differentiate where extension and dimension lines begin and end. Furthermore, since all line weights are the same weight on CAD drawings, it significantly increases the difficulty of reading the print. In addition, extension and dimension lines cross object lines without a break, which, again, is not consistent with standard drafting practices.

NOTE #2: The drawing is zoned much like a travel map. Letters on the right edge of the drawing are for locating an approximate vertical location of a part. Numbers on the bottom edge are for locating the approximate horizontal location of a part. By crossing these locations (coordinates), an approximate location of a part can be found. The zoning process expedites the reading of a drawing print.

NOTE #3: The section drawing does not include section lines to show where the cutout of the part was made. Although this is not standard practice, companies may apply their own standards in the preparation of drawings. Eliminating a section lining reduces time in preparing drawings.

However, section lining is the preferred practice for clarification purposes.

1. a. Sketch a welding symbol to illustrate the welds specified on the drawing including dimensions.

b. List the applicable notes for the welds required including location of weld specified.

3. Identify the views shown.

4. a. What is the significance of the symbol shown on the drawing surfaces?

b. What tolerance is to be applied?

5. a. List the specifications for the.750-10 UNC tapped holes.

b. Interpret.750-10 UNC.

6. a. Describe part

b. In what zone is it located on the drawing?

7. a. Prepare a two-view orthographic sketch of

item (7 .

b. Place a note on the sketch specifying the kind of material that is to be used.

8. What is the significance of dimensions enclosed in parentheses?

9. The dimensions that follow, as found on the drawing, are incorrect in accordance with drafting standards. Sketch correct versions.

Incorrect 1.50 R

2. What type of drawing is illustrated?

2.032 Drill

1. 0 R

10. a. What kind of material is specified for item (3 ?

19. What is the purpose of the dimension shown on the left edge of the drawing as follows?

20. What scale size is used for this drawing?

b. List its size and quantity required.

11. What type of material and its size is specified for item $0 ?

21. What is the overall size of the “Die Stand Frame”?

12. What style of numerical dimensioning is used?

13. What is the purpose of identifying the zone locations for each item?

14. Prepare an isometric sketch of part ^ and dimension it.

15. Prepare a two-view orthographic sketch of part (4 and dimension it.

16. a. In what zone is part

b. Prepare a two-view orthographic sketch and dimension it.

17. a. What quantity is required for part ^ ?

22. List the dimensions for part

23. What is the angular spacing of holes shown equally spaced on a 14.500 0 ?

24. What is the ream size specified for the two holes after completion of welding?

25. How many pieces are required for making the “Die Stand Frame”?

26. What is the center-to-center spacing between parts (0 ?

27. a. What is the spacing size between the rectangular steel tubing?

part (9 ?

b. What material is to be used?

18. Identify the kind of drawing showing parts M,

(2 , (3 , (5 , and (g.

®--------------------------------------------------------------

<2---------------------------------------------------------------

(3-------------------------------------------------------------------------------------

d---------------------------------------------------------------

(8--------------------------------------------------------------

b. What are the hole sizes for

28. a. How many flame-cut holes are to be made?

b. Identify the item(s) to have a flame-cut hole.

29. Where extension lines connect to object lines, make a red check to indicate where there should be a break.

30. Where dimension lines do not show a break when crossing object lines, make a red check mark to indicate where breaks should be made.

31. Add section lining to show where the rectangular tubing has been cut. Select the appropriate view to show this. Also, section lines should represent the kind of material for these parts.

32. Which dimension(s) found on the drawing is/are shown as a common fraction?

33. What is the significance of A/R?