CAD
CAG

 The computers ‘Brain’
 A large micro chip that controls the computer and carries out all the instructions and data handling

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 Used to input text and numbers into the computer

 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

 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

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

 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.

 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.

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

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

 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

 A modem is both an input and output device
 Data can be exchanged with drawing offices across the world electronically

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

 Portable removable storage
 Only holds 1.44 MB of data
 Can be used in most computer systems
 Easily damaged

 Large capacity storage
 Not portable – build into base unit of computer
 Fast saving and retrieval of data

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

 High capacity portable storage
 Needs a CD writer to store data

 You must know for your exam the following common CAD commands

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

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

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

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

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

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

This allows the user to change the size of an object
This flips an object about the horizontal or vertical axis

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.

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.

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.