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Technical drawing and CAD

What should you know before starting this unit?

This unit is a continuation of Graphic representation. In that unit we already studied some basic concepts that you should remember:

  • The difference between perspective drawing and multiview projection.
  • The mail views used to represent figures: front view, side view and top view.
  • How to represent easy slated faces, that is, faces that are visible from more than one view.
  • The basic dimensioning rules and its application to easy figures.
  • The difference between chain and parallel dimensioning.

Lesson 1:

Handmade drawing and computer drawing.

Graphic representation is used in the vast majority of technological projects. As we saw in 1st of ESO, drawing is a way of communication that, contrary to spoken or written language, is understandable by everybody, in every country. Thanks to graphic communication we can easily transmit ideas that otherwise would be really difficult to share. Think about how easy it is to help a tourist by drawing a route on a map, for example, and how difficult it is to represent the same idea with words, mainly if you don’t know the other’s language.

But once the importance of drawing as a way of communication is clear, we can ask ourselves one question: it is better a handmade drawing or a drawing made with computer software? As it usually happens with this kind of question the answer must be: it depends.

(Land8: Landscape Architects Network)

But what does it depend on? I’m going to answer that question with another question…

Imagine your at home, having breakfast, and suddenly realize that there is only one bottle of milk left. You decide to take note of it because, otherwise, you’ll probably forget next time you go to the market. You have two options:

  • Taking a post-it from the table in your room, write the word «milk» and then paste it in the door of the fridge.
  • Go to your bedroom, turn the computer on, open Word or similar software, write the word «milk», turn the printer on, introduce a sheet of paper, print the file cut out the sheet of paper (because you are not going to paste the whole sheet) and finally paste it in the door of your fridge.

Of course, with the second option the result will be perfect: all the words with the same size, no writing mistakes, cleaner… However, is not worth spending so much time for such a thing, ant the first option is, by far, more practical.

Just the same happens with graphic representation. Depending on the situation one or another option will be better. Hand drawing has some advantages that computer drawing doesn’t and the other way around. That’s why knowing how to use both of them is the clue to be more efficient:

  • Hand drawing: will be the best option when we need to make a quick drawing to transmit an idea to another person but there’s no need for too much detail or accuracy in the dimensions.
  • CAD software: must be chosen when we need to communicate an idea with a high degree of accuracy without any kind of mistake, or when a good presentation is essential.

Let’s see some situations in which one of the two options must be chose:

  • We are in a furniture store and we want to explain the layout of our room to the store manager to help us choose a shelf that fits in the available space: hand drawing.
  • We are solving a math problem and a drawing can help us find the solution: hand drawing.
  • We want to renovate our house so we are going to change the distribution of all the rooms by bringing down partitions and raising new ones. Therefore we need to draw a plan for the bricklayer who is going to carry out the work: computer drawing.
  • You are designing the new urban garden of your high school and you want to represent quickly and in an approximate way the location of the different plants in the available space so that your classmates know where to sow each type of seed: hand drawing.
  • You work in a company that has been commissioned to design a fundamental part for a car engine: computer drawing.

Along this term will work with both types of drawing, this way you’ll to have the chance to chose the best option in each situation.

2D and 3D computer aided drawing (CAD).

The first thing you should know about computer drawing is that the applications we use to create drawings on a computer are called CAD software, which stands for: Computer Aided Drawing software. There are plenty of CAD software as we say in the unit 3D printing in 2nd of ESO. From the most basic (such as Tinkercad for example), that are usually free, to the most professional ones (AutoCad, Catia…), whose licenses can cost thousands of euros.

The second thing you should know is that there are two types of CAD software: for 2D drawing and for 3D drawing. For example, when drawing the plans of a house are usually made wit a 2D CAD software, while the design of an aircraft requires a 3D software:

(Plano de vivienda, Anton Raath, flickr)

Some software only offer one of the two options. Some examples are QCad (image on the left) that is just intended for 2D drawing, or Tinkercad, which only allows 3D design. Both software are free and are widely used in high schools.

(Qcad design,

(Tinkercad design,

However, it is quite common to find CAD software that includes options for both 2D and 3D drawing. This is, for instance, the case of SketchUp, which allows us to create 2D drawings (image on the left) as well as 3D designs (image on the right) in the same application. This software is not completely free but has a free 15-day license as well as an online version with some limitations.

(Diseño con SketchUp.model by John Luttropp ,

(Diseño con SketchUp, Ryan Homes Avalon,

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