Originally technical drawings were just used to convey an idea, showing the basic way a device would be constructed, parts were shown to an approximate scale but no exact measurements were given. Notes on the drawing were critical to its understanding, giving an explanation to way the device was intended to function. It was then up to the designer and manufacturer to collaborate to assemble a working version of the device. Artists and designers such as Da Vinci pioneered the use of specific geometric views display an idea in a way that was easy to visualize.
Up until the 20th century technical drawings would remain at the level of a sketch, usually accompanied with a wooden model to demonstrate the main principles. This wooden model was often used as the main template for actual manufacture. With the development of standardized and interchangeable parts the role of the technical drawing became a much more important one. Before the advent of a interchangeable parts a manufacture would simply create a part that worked or fit for the application and then just keep replicating that part. Now with standardized screws, nuts, bolts, springs and shafts being manufactured on a large scale which made them cheaper to buy than producing an individual batch yourself engineering drawings were needed to call which standardized part was supposed to be used were. Also with the standardization of technical drawings themselves a drafter could send a drawing out to a manufacturer who would know what all of the symbols and nomenclature meant and he would be able to a return a finished product just as the drafter has intended.
Recently there has been a separation of manufacturing oriented drawings and educationally oriented drawings. Most technical drawings used are simple wire frame views of a component that show dimensions and other information for productions but contain little information on the function of a product. Technical illustration is a term that is now used to describe the colored and shaded drawings of a product that often show a cut away section revealing the operating mechanisms. I remember fondly seeing these types of pictures in the way things works books and issues of popular science. I will probably make another post with pictures of some pretty hilarious patents that I have seen floating around.