It wasn't long ago that designers, architects and draughtsmen used specialised drawing boards and drawing pens to design things for craftsmen to make. Computers haven't entirely replaced these skills but they have removed many of the more boring and repetitive parts of the design and manufacture process.

When producing an engineering drawing by hand it would take a skilled draughtsman many hours of concentrated work. If the draughtsman then made a mistake, or smudged the ink, he or she would have to start all over again. Also, using such big paper it is difficult to make a photocopy of the final design - so copies had to be made using complicated procedures such as making 'blueprints'.

In the same way as a word processor helps someone to write and print a piece of text, a CAD package is a piece of application software that helps someone to make engineering drawings.
The various tools available in the CAD software varies from package to package, however, most allow the designer to plot simple shapes (circles, rectangles, triangles, etc) accurately. It also allows the designer to place these shapes next to each other with the same accuracy using tools such as on-screen rulers and grids.

The drawing shown here looks like it has been made out of wire and it is referred to as a wireframe view. This particular drawing also has hidden-line removal: any lines at the back of the object (which wouldn't normally be seen) have been missed out to make it clear.

When the drawing has been finished the designer can check to see what the final design will look like. This is also done by the CAD software through a process called rendering. The software shades the drawing so that it gives the impression of a three-dimensional object. In more complex CAD packages the designer can select different materials, colours and textures during the rendering process.

In this way the CAD software has created a model of the object which can be evaluated by the designer before the object is ever made. At this stage, any changes in design can easily be made - and the results seen immediately on the computer screen.

Most modern printers are capable of producing very good, accurate engineering drawings. Not long ago, though, printer technology was not capable of producing the clean, straight lines required by engineers and designers.
Many of the printers available worked by shading in many small dots on the paper to produce the final picture - or bitmap image. What was needed was a printer that produced a vector image: one that was based on lines rather than dots.

The plotter is a special type of printer that is used to produce vector images (as opposed to the bitmap images made by laser, inkjet and dot-matrix printers).

Plotters are still used today, however, as they are able to accomodate the large paper sizes favoured by engineers and architects. This allows the draughtsman to produce a drawing with lots of detail without the final drawing being too small.

The plotter uses special pens instead of ink, toner cartridges or ribbons. Some pens are simple fibre-tips while others are more specialised drawing pens.

The pens are loaded into the plotter when it has first been switched on. The designer has to provide the correct number of colours and nib sizes for the required drawing. Once the plotter is running then it can only select from the range of pens given to it at the start.

The final image produced by the plotter should have clean, crisp lines and simple colours: just what an engineer needs in order to make something.

The picture shown here is a plot made by a plotter of itself. The original picture was a vector image (because it was made up of straight lines). However, I scanned the image (which converted it to a bitmap: made up of many tiny dots) and you are probably looking at this page on a raster monitor or even on paper from a bitmap-based printer so it doesn't look as good as it should.
(also the ink on the black pen was running out a bit!)