1. Graphic Communication
CAD/CAG Revision

2. Computer Hardware Processor Input Devices Output Devices
Storage Devices

3. CPU Central Processing Unit
The computers ‘Brain’
A large micro chip that controls the computer and carries out all the instructions and data handling

4. Computer Hardware
Input Devices

5. Keyboard
Used to input text and numbers into the computer

6. Mouse Used to guide a pointer or cursor around the screen.
Functions are selected with the aid of the control buttons
Some mice have a wheel which is used for zoom and scrolling

7. Tracker Ball This device is very similar to a mouse.
It is used where there is little desk space available for a mouse
The large ball is on the top of the device and is rotated using the palm of the hand

8. Joystick Used commonly for games
Used in many simulation situations. E.g. Flight and tank simulators

9. Graphics Tablet Used for sketching or tracing drawings into a computer
Uses a puck or a pen to detect the exact position of the cursor on a drawing etc.

10. Digital Stills Camera
This camera stores the pictures it takes in digital form. These can the be downloaded to a computer for inclusion in a DTP document etc.

11. Scanner
Used to electronically convert paper images to to computer files.
Text can be scanned in using OCR (Optical Character Recognition) software
Flat bed Scanner
Hand held Scanner

12. Computer Hardware
Output Devices

13. Flatbed Plotter Only used by CAD programs Produces line drawings
Page size is limited by size of plotter bed
Not suitable for printing pictures

14. Drum Plotter
Drum plotter are usually used in industry to produce large drawings (up to A0)
Paper moves back and forwards while pen moves from side to side

15. Fax/Modem A modem is both an input and output device
Data can be exchanged with drawing offices across the world electronically

16. Storage Devices
A PC usually has several methods of storing data on it. These may include a mixture of fixed and removable storage systems

17. Floppy Disc Portable removable storage Only holds 1.44 MB of data
Can be used in most computer systems
Easily damaged

18. Hard Drive Large capacity storage
Not portable – build into base unit of computer
Fast saving and retrieval of data

19. Zip Disc
Similar to floppy disc but greater storage capacity (100 – 250 MB)
Portable
Not all computers have Zip drives

20. CD Rom
High capacity portable storage
Needs a CD writer to store data

21. CAD Commands
You must know for your exam the following common CAD commands

22. CAD Commands 1
An on screen grid which can be set to any size. Can make it easier to do orthographic drawings
An on screen grid which is set at 30 deg. Can make it easier to do Isometric drawings

23. CAD Commands 2
This restricts the start and end points of lines to a predefined grid
This allows different types of information to be keep separate on a drawing

24. CAD Commands 3 Allows the drawing of rectangular shapes on screen
Allows a user to increase or decrease the screen view so that they can see more detail

25. CAD Commands 4
Allows the user to copy and position objects or parts of a drawing without having to redraw them
Allows the user to draw arcs and circles on screen

26. CAD Commands 5 Fillet puts a radius on a corner (rounded)
Chamfer puts a 45 deg angle on a corner
This allows the user to draw circular or rectangular arrangements from a single object

27. CAD Commands 6 Trim/Break removes an unwanted section of line, etc.
Extend makes a line, etc. longer (usually to meet another object)
This allows the user to turn an object at any angle about a point

28. CAD Commands 7
This allows the user to change the size of an object
This flips an object about the horizontal or vertical axis

29. ADVANTAGES OF A CAG SYSTEM OVER A DRAWING BOARD 1
Storage and retrieval
A completed drawing or series of drawings can be stored on hard drive, floppy disc, Zip disc or CD-R. These formats require less storage space than paper drawings. The drawings can then be printed as many times as required with no deterioration in quality.
Ease of modification
Companies who use CAG systems have advantages over competitors who rely on more traditional methods of modifying drawings. The ease and speed with which modifications can be made reduce time and costs, which in turn increases productivity.
Repetitive elements (library)
Drawings can contain a number of repetitive elements such as doors, windows, kitchen fittings and appliances. It is useful to have these items stored in a CAD library file. CAD library files are available for mechanical engineering, architecture and electronics. Items that you design need only be drawn once, saved to a library file, then retrieved and positioned each time they are required on a drawing. This saves time and effort, which increases productivity.

30. ADVANTAGES OF A CAG SYSTEM OVER A DRAWING BOARD 2
Drawing speed
It does take a considerable amount of time and financial investment by companies to train their CAG operators. In relative terms, however, drawing production is much faster using CAG than using traditional methods, so the company will save time and money in the long run.
Standardisation of drawings
Standardisation of drawings is often determined by drawing standards such as 851. Standardisation of drawing layouts and styles can easily be created in the 'in-house' or corporate style adopted by the operator or the company.
Drawing size and flexibility
Drawings can be enlarged or reduced with no loss of detail. Extremely fine, detailed work can be produced using commands such as ZOOM. Positive location tools such as GRID, GRID SNAP and ATTACH enable accuracy to be maintained even in the smallest details.

31. DISADVANTAGES OF A CAG SYSTEM compared to DRAWING BOARD
Viruses
Viruses can infect a computer causing them to run slow or even lose all the data / drawings which have been saved. Good anti virus software is required and should be updated regularly.
Cost
The cost of the initial set-up of a computer network with full professional software can be expensive and it then requires frequent maintenance and upgrading.
Hacking
Computers could be hacked into to steal company secrets or new design ideas
Training
Initial training for employees and then regular updating of skills will be required.
Powercuts
Data could be lost if not saved when a powercut occurs. A prolonged powercut will mean no work can be done on computers but employees would still need to be paid.