INTRODUCTION TO ENGINEERING DRAWINGS

Audio: Introduction to the engineering drawings

In my previous article, technical production documentation, we looked into the different documents that mechanical design engineers create to communicate and validate their design intent. In this article, we will discuss one of the most represented ways of engineering communication – engineering drawings.

Throughout history, humans have been communicating in different ways. We have been using hand gestures, pictures, objects, language, etc. As time passed, language evolved, and it took the primary form of human communication. At this point, every language in the world has a clear set of rules (grammar and spelling) on what is considered to be and not be a proper way of communication. If no rules were defined, clear communication would be hard to achieve.

The rules play a vital role in our lives; they ensure that we are standardizing things to achieve the desired outcome as fast as possible without any ambiguities. In the same way, as we communicate every day with people around us, design engineers need to express their intended design with other people who may or may not speak the same language as engineers. Thus, one of the most represented ways of communicating the design intent is engineering drawing. Similarly, as every country has its own set of grammar and spelling rules, engineering drawings also have their own set of rules defined by standard organizations.

Introduction to engineering drawing

We can observe engineering drawings as a unified language that engineers use to communicate independently of each other’s spoken or written language. The engineering drawing rules are defined and embodied in the publications of standards organizations (for example, ISO and ASME).

According to ISO 29845:2011, drawing is “technical information, given on an information carrier, graphically presented in accordance with agreed rules and usually to scale.” Although engineers created the engineering drawings in the past by hand, today, they are primarily done in CAD software like Autodesk Fusion 360.

Creating drawings using the CAD software is a straightforward process; we make (or
import) a 3D model, and then we start inserting the views in the drawing and adding dimensions.

Simple right? It is simple for nonprofessionals. It is pretty easy to learn the commands in the software but knowing which rules to apply and why is not quite simple. Always keep in mind that software is only smart as much as the person using it.

Let’s look at the following example. Imagine that you are designing a simple steel plate. You are designing in Europe, where the standard measurement system is the metric system of unit measurements. You are sending a hand sketch with only outline dimensions to your supplier in the USA using the imperial system of unit measurements. For the sake of argument, let us say that the steel plate dimensions are 100x50x10 mm.

Your USA supplier confirms the order, and you receive the steel block with the dimensions 2540x1270x254mm. If you converted the given numbers back to inches, you would get precisely the same numbers as you defined them on the drawing. The “ only” thing missing is that you didn’t specify the units of the measurement on the drawing. Looking at this simple example, we can see why creating a clear set of rules and norms are imperative for engineering drawing.

Application of engineering drawings

You may ask yourself, where do we use engineering drawings?

I am not exaggerating when I say everywhere. With the use of engineering drawing, professionals have built everything physical around us. Furthermore, engineering drawing is the most used way of communicating between the mechanical design engineer and everyone else in the production chain.

For example, commercial cross-Atlantic airplanes contain millions of different components. These components make up various sub-assemblies and assemblies, and so on. These assemblies and components must be physically manufactured and constructed in a safe and reliable product, a.k.a airplane.

Let us now look into some other examples:

Requirements of the engineering drawings

Engineering drawings are legally binding. That means your manufacturer is not legally obligated to refund you for the faulty parts if he created them according to the specifications on the drawing. Also, the manufacturer is protected from liability, and he is not responsible for any material damage (or possible injuries) that could be caused by using those parts.

Therefore, engineering drawings need to meet the following requirements:

Engineering drawings must conform to the relevant industry standards ( ISO, ASME). Alternatively, standards can be used that are applicable within countries. Also, the engineering drawing must be as language-independent as possible. Therefore, the standard-defined symbols should be used wherever possible (keep in mind that standards can be translated in different languages, but symbols still hold the same meaning).
The content of the engineering drawing should be clear, and there should not be room for ambiguity. For the artifact to be manufactured according to the drawing specification, there must be only one possible interpretation.
This should go without saying, but the engineering drawing must be completed before releasing it. All relevant manufacturing information should be stated: dimensions, tolerances, applicable standards, symbols, surface finishes, surface treatment, heat treatment, special notes, etc.

As we can see, the process of composing an engineering drawing (drafting) is not to be taken lightly. Composing a clear, unambiguous, and complete drawing according to the applicable standard requires a great deal of learning and practicing.

As a mechanical design engineer, you will surely come across a detailed and assembly drawing. So let us have a look!

Engineering drawings example – Detailed (part) drawing

According to ISO 29845:2011, a part drawing depicts a single part that cannot be further disassembled and includes all the necessary information required to define the part. Everything needed to manufacture the single part is defined in the part drawing, e.g., the form, dimensions, tolerances, material, finishes, treatments, etc. The building blocks of the engineering drawings are as follows:

1. The drawing border defines the limit of the formal drawing area. It means that every content relevant to this drawing must be inside this border.

2. The title block contains all the relevant information needed to identify the drawing, e.g., part number, part name, drawing owner, designer name, etc. Furthermore, a title block defines other relevant information, e.g., material, standard, perspective type, scale, page number, etc.

3. Notes are used to specify other equally important information needed for complete drawing specification, e.g., overall surface finish or surface finish specified for a particular surface, material (in this case in Title block there should be written “see notes”), color, reference to CAD model, etc.

To learn more about the drawing borders, title blocks, notes, and other essential elements of engineering drawing (font, sheet sizes, scales, etc.) read Basic elements of engineering drawings.

4. Main orthographic views are used to draw 3D objects in 2D. The main view (front view) always shows the face with the most details. We can project other views from the front view, and there can be a maximum of six orthographic views. The number of views depends on the complexity of the 3D object.

5. Isometric projection provides the visualization of the 3D object. It belongs to the “Pictorial projections” group, specifically the axonometric projection. Isometric projection is an addition to orthographic views and is extremely useful for visualizing complex objects.

To learn more about orthographic views, isometric projection, and other important projections used to represent an object on an engineering drawing, read Projection methods on engineering drawings.

6. The section view is used to show the internal geometry of the part. The process of creating the section view is called sectioning. We are using a plane to cut through the object to gain clarity of its internal features.

7. The detailed view is used when the detail of the object is not visible due to the scale of the drawing. In that case, we are using a thin line to circle out the object detail and enlarge it to an appropriate scale. The area inside of the circle represents the enlarged area.

To learn more about the section and detailed views on an engineering drawing, read Section and detailed views on engineering drawing.

Engineering drawings example – Assembly drawing

According to ISO 29845:2011, an assembly drawing represents the relative position and/or shape of a group of assembled parts. The assembly drawing is not showing the manufacturing details of a single part but merely how the individual parts are supposed to be assembled. The main assembly consists of subassemblies, parts, and materials.

8. An exploded view is used on the assembly drawing to show the relationship of the parts in the most realistic manner.

To learn more about the exploded views, read Projection methods on engineering drawings.

9. A parts list or Bill Of Materials (BOM) – The parts list defines the list of the object’s elements. The bill of materials is a list of the subassemblies, parts, and materials required for building the assembly. The parts list or BOM can be added directly to the drawing or provided with the assembly drawing as a separate list. The difference between the parts list and BOM is that the parts list defines only one structural level.

Additional tables are used to display information about the part specification (e.g., color specification for the same parts), design (e.g., product families), or any other suitable information for tabular representation.

To learn more about the Parts list, read Basic elements of engineering drawings.

Closing words

A great deal of practice is required to become an expert draftsman. As a mechanical design engineer, engineering drawing is something that you will encounter on a daily basis. You can think about engineering drawing as a fundamental piece of information in mechanical engineering; hence the art of reading and creating the drawing is fundamental knowledge for any mechanical engineer.

The better you understand the rules for drawing creation and the CAD tools you are using, the faster and more efficient you will become. The sooner you internalize these rules, the sooner you will unburden your brain and create a space for other important technical knowledge. You can learn to design anything, but your design is useless if you cannot communicate it properly.

Now you have an excellent overview of what engineering drawing is all about. However, I suggest you go through the text once more and identify areas you think need more understanding and clarity. Then, once you have identified those areas, start building up your knowledge in those areas.

To make it easier for you to find related posts, check the “Further reading” chapter below. Do you have any questions or need something to be clarified better? Leave a comment below, and I will give my best to adjust the post accordingly.

Do you like what you read? Then, share it with your friends, colleagues, and on your social media channels. And if you want to become a part of the Newtonians, make sure to subscribe to our newsletter!