SECTION AND DETAILED VIEWS ON ENGINEERING DRAWING

Audio: Section views and detailed views on engineering drawing

In Introduction to engineering drawings, we showed you the building blocks of engineering drawing. Sometimes using main orthographic views is impossible to show all the features of an object to the degree that the object is sufficiently described for manufacturing. In those cases, we have very powerful tools available to us. In this article, we will discuss the types of section views and detailed views that will assist us in clarifying our design intent. Before starting with this text, I suggest you familiarize yourself with the Projection methods on engineering drawings.

Section views

Most of us have seen lumberjacks with the chainsaw in action, either live or on TV. They take a log, start a chainsaw and cut it into two pieces. The cutting results are two pieces of log, and if we looked into the face of one of them, we would be able to see wood rings.

Let us look at this from the engineering perspective. A similar principle stated above, we are using when creating a section view. The only difference is that we are cutting virtual objects, and we are not using a chainsaw. So, imagine that we have a virtual object (log) and are using the virtual cutting plane (a chainsaw) to split our object into two pieces. The result, when looked into, would be a section view (wood rings).

If our object has a complex geometry and we need to show this geometry clearly and unambiguously, the most convenient way is to use a section view. Not only is using section views the most convenient way but using section views is the best way to show the object’s interior. As I said, this is accomplished using the virtual cutting plane cutting through the body. Like our example with the chainsaw cutting logs in two pieces, we are doing the same to our object on the drawing.

The picture above only represents the idea of cutting the object, but on the engineering drawing, this is not how we will display the section view. Moreover, the rules for creating section views are strictly defined by ISO 128-3:2022.

Elements of the section views

The picture below shows how our object would be represented in the engineering drawing. The main elements of the section view are:

section line,
section reference arrow,
section reference letters,
hatch.

We will go step by step, explaining every element of the section view.

Section line – considering that 3D object representation is used for the visualization (pictorial projection), for specifying object dimensions, we are using orthographic projections. Bearing in mind that the orthographic projection represents the object in 2D, we have to somehow represent the 3D virtual cutting plane in 2D. For that, we are using the section line. In the picture below, we can see our object cut in 3D with the virtual cutting plane. If we would look at the object in 2D from side A, we can see exactly what our section line is representing: the position of the virtual cutting plane in 2D on our object

Section reference arrows – on the picture above, we saw the transition of the cutting plane from a 3D to a 2D orthographic view. But we will not show a 3D projection of the virtual cutting plane position and the direction of view on the 3D object every time we create a section. Instead, we will only create an orthographic view and create a section from there. We are going to point the direction of the section view with the use of the section reference arrows.

Section reference letters – now look at the picture above. We have defined the section line and the section identification arrows, but there is still something missing. A section identification letters! Imagine that you are creating a drawing with 10 different section views. It would be difficult and time-consuming to match every section line with its corresponding section view. In order to maintain clarity and unambiguity, we are adding two equal capital letters to the section identification arrows. When you look at the picture below, we can see it is quite easy to find any section view on the drawing. Keep in mind that if your section view is displayed in a different scale than the overall drawing, that should be indicated below the section identification letters.

Hatch – now look at the picture above one more time. Looking at the section view, it is hard to understand which area is cut and which is not. To make this clear, we are using crosshatching. Every surface that is cut is marked with a thin line, 45° tilted with respect to the main contour. We are calling this surface pattern a hatch.

Let us now look at our orthographic view with a section view without any remarks on the picture.

And this is my friend, how you create a section view on the engineering drawing.

Of course, the ISO 128-3:2022 standard defines the type of the section line and the shape and size of the section identification arrows, fonts, etc. But as we are using CAD software to create the drawings, CAD software has already implemented ISO rules. For that reason, these details have been left out of this text.

Now that we know how to create a section view and the elements of the section view, the story about the section views does not end here. The example I showed you before belongs to the group of full sections. We also have modifications of the full section: offset and aligned sections. We also have half and partial sections. And partial sections, we can further divide into breakout and crop sections.

Full section views

The full section represents a complete section of the body, i.e., the virtual cutting plane extends through the complete object. We have already shown you the example of the full section.

Offset section views

We can consider the offset section to be a modification of the full section. In the offset section, the virtual cutting plane theoretically cuts through the whole object, except that the cutting surface is stepped. The changes in directions are 90°. The size and location of each step are not strictly defined; it depends on the geometry that we would like to show with the section view. Using a stepped virtual cutting plane, we can show more details with one section, for which we would usually need multiple section views.

Aligned section views

Like the offset section, the aligned section cutting plane changes directions, usually in the range of 0<α< 90°.

Half section views

The half section shows both the view and the section. The centerline on the section view separates the unsanctioned view from the sectioned view. The hidden lines should remain hidden unless they improve clarity. The half section is really useful when we have a symmetrical part around the plane or the axis.

Partial section views

The partial section views are used when the internal contour in certain areas wants to be exposed and when the full section would not reveal any additional details. Often partial section is also called the breakout section.

Conventional breaks

Imagine that you have to create a drawing of a pipe that is two meters long with two flanges, one on each end. In order to fit this part on the drawing, you must use a large reduction scale. For example, in the drawing below, I used the A3 sheet size with a scale of 1:20.

In these cases, when we have long objects with constant shapes throughout their length, we can use a conventional brake to shorten it on the drawing. This allows us to use a smaller sheet size, save space on the drawing, and use a bigger scale. In the drawing below, I used the conventional brake on A3 sheet size with a scale of 1:2. If you compare the previous drawing example with the example below, you can see that clarity of the drawing is improved drastically.

Unsenctioned features

When creating a section view, some of the components or features are intentionally left unsectioned because sectioning them would not give a clear definition of the object.

The Components like shafts, studs, rivets, pins, screws, nuts, washers, feather keys, rolling bearing bodies, knobs on handwheels, lugs, ribs, spokes, gear teeth, etc., are left unsanctioned.

Usually, these components and features are cut only transversally and not longitudinally.

I already mentioned that you will most likely use CAD software to create drawings (and on the drawings section and detailed views). Unsectioning different components in CAD software like Fusion 360 is a straightforward process. For example, when creating a section view, Fusion 360 automatically gives you an option, “Objects To Cut” where you can simply choose which parts you want to cut or leave uncut.

Detailed View

When we have a main orthographic view in a scale that does not allow all the features to be clearly represented, we can use a detailed view to enlarge these details. The detailed view is one of the elements you will often use when creating the engineering drawing. Let us take a look into the main element of the detailed view.

The viewing line is placed around the area that we want to enlarge. It can be created as a circle or freehand line around that area.

Detailed view reference letter have the same purpose as section reference letters. We are using it as a detail view identifier. Every detail view should be marked with a capital letter placed near the viewing line and above the detail. I usually like to add the remark “DETAIL” in front of the reference letter. Also, considering that detail view is used for enlarging certain objects, features scale needs to be displayed. I usually add the remark “SCALE” in front of the actual scale. As I already said, when you have many sections and detailed views, I believe that it adds certain clarity to the drawing.

Let us now look at our detail view without any remarks on the picture:

Closing words

Using section and detailed views on your drawings increases the clarity of the drawing. In order to get a full grasp of when to use section and detailed views requires practice. But like in everything else, the more you use and practice it, the better you will get.

With the usage of CAD software, creating section and detailed views is easy and straightforward. With just a few clicks, your CAD software will create a section view, hatch it, scale it, etc. But still, you don’t want to be one of those engineers clicking things around, not caring or knowing why you are doing it. Always keep in mind that software is as smart as the person using it.

Now you have a great overview of the section and detailed views on the engineering drawing. 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.

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