This post is about third-angle orthographic projections for drawings.
Read the first blog post on first-angle projections to get up to speed with this article.
The key difference between the 1st-angle and 3rd-angle, in a nutshell:
- For first-angle, we place the object on top of the drawing table and roll it around, tracing the shadows it casts underneath the object
- For third-angle, we place the object inside the drawing paper, and roll it around the inside surface of the paper, like the object is trapped inside a glass box (just like it is inside your PC monitor)
In the image below we see the front view being projected onto the surface of the box that is between the model and the viewer:
The more common analogy explaining the difference between the systems is of unfolding a box: the object is inside a box and the drawings are projected outwards onto the planes of the box. Then, we unfold the sides of the box to be flat:
- For 1st-angle, the drawings are on the inside of the box and we unfold from the front, so that the flattened box sits behind the object from the viewer's perspective.
- For 3rd-angle, the images are drawn on the outside of the box, and we unfold it from the back so that the flattened box sits in front, in-between the viewer and the object.
What is so good about 3rd-angle? well the drawing views are arranged around the front view on the same side as what they are named!
"Right" views are placed on the right hand side, "left" on the left, and "top" views are drawn above the front view, etc. For most laymen and beginners trying to make a model or part from a drawing, this layout makes it much easier to imagine and realize the shape.
Please read the first blog post for an overview of how drawing arrangements end up backwards in 1st-angle.
But don't forget that only the arrangements are backwards. A view named "right view" is always the right view of the model, and will show the proper side of the model regardless its position on the drawing sheet.
The real professors among you though will remember that the proper "right" view shows the model's left side, and vice-versa - but this is an issue shared by both 1st and 3rd-angle views.
Though many people consider 3rd-angle the "more intuitive," or dare I say "modern" method of projections, we should recognize that 1st-angle is perfectly functional. For the original modern engineers of the Industrial Revolution, 1st-angle made the most sense as they sat at their drawing tables with a widget in their hand and the drawing paper behind it. Today, 1st-angle is still the system used by "the rest of the world"; the standard in Europe and almost all Asia, apart from Japan.
3rd-angle came into prevalence mostly with the rise of the United States as an industrial power. I am quite sure it was invented in the Old World, but third angle certainly rose to dominance in the New World.
Some UK firms did shift to 3rd-angle during WWII in order to cooperate with America during the war effort, and so now they still use it. I have also heard European architects say they use 3rd-angle because to make views of a huge structure it makes more sense to physically walk around it and hold the drawing sheet between the viewer and the building. Here you can read one of many posts on Reddit with varying perspectives from real engineers who had to deal with 1st-angle. (Keep in mind that Redditors are a US-centric group so the perspective there may be skewed)
Nowadays, 3rd-angle is the standard in all of the Americas, Australia, and Japan. Basically, over the last 100 years we have stacked the engineering influence of Europe up against that of America and Japan. Even if it seems like 3rd-angle has had the momentum recently, the still-rising titans of India and China using 1st-angle probably means it is not going anywhere.
In any case, it is a global world, and you might be working with clients from opposite sides of the planet; the boundaries between countries mean less than they ever did before. You might even be working on one project that has to incorporate drawings in both projections. Being aware of and able to use both systems when you need to is a necessary skill, so read on!
Remember that it is only when drawings on paper get involved that we need to know about projections. Modern design and manufacturing relies heavily on the use of digital 3D models, and it just so happens that the paradigm of viewing a freely-rotatable model on a computer screen actually completely erases the need for a complex and obtuse system of projecting views onto planes. Computer screens are a wonder of the modern world that youngsters can take for granted, but remember that it is an innovation less than 50 years old.
If we never have to show two different views on one piece of paper, there is no need to worry about which view should be placed left, right, above, or below. Instead, on the computer screen we simply rotate the model to look at the side we want to.
However we still look at the model in space with named views that are just like the drawings. We have a 'front' view in the software that is of the front of the model, and not to the front of the model's 3D space. In fact, our 'front view' shows us the 'back wall' of our 3D space, behind our model. This is that philosophical question again; something is going to get reversed.
So, surprise surprise, when we 3D-model something facing us in front view, and then choose the 'left' view in our CAD system, we will see the model's right side, and vice-versa
If you've been paying attention, you might notice that the layout of the default 4-view in SolidWorks follows the 1st-angle convention: the "left" view is placed to the right and 'points away' from the front view, and the "top" view is placed below and also looks away. Vive la France! — Maybe this is why I have always had trouble using the 4-view in SolidWorks; my brain just doesn't like parsing 1st-angle.
But the layout of the views in a 3D window doesn't really matter. Many modelers spend 100% of their time in a single viewport, tumbling or selecting named views from the Orientation popup (Spacebar by default in SolidWorks). This tumble-and-look approach is always intuitive, and we rarely have trouble making models from imagination.
But don't think that you can escape drawings! People in the machine shop require multiple 2D views of the part they are going to make for you. Even if your manufacturing is completely CNC, documentation standards of the company likely require 2D drawings, not to mention the patent office, government regulatory agencies, et cetera, et cetera. Maybe drawings will be dead 200 years from now, but they are alive today, and we have to get in bed with them, and make them breakfast too!
So, going back to our concept of the model 'inside' the drawing plane, how do we make 3rd-angle drawings, and what do they look like?
In 3rd-angle, we grab one of the front edges (nearest the camera) of the model's bounding-box cube and keep it stationary, and then rotate the model around that edge (whereas first-angle rotates around one of the back edges). In the following image, the rotation-axis edge of our man in the glass box is highlighted in purple, along with the resulting top-view projection:
After the rotation is done, we draw all the lines that we can see on the surface of the glass box that lies between the object and the viewer. Unlike in 1st-angle, 3rd-angle's top view is placed above the front view. Intuitive!
Moreover, when we roll the cube around its side edges, the 'left' view (remember that 'left' view shows the model's actual right side, etc.) will be placed on the left, the 'right' is positioned on the right, and the 'bottom' on the bottom. Hallelujah! As discussed in part one, the back view can be placed anywhere, but either below or on the extreme right-hand side are most common.
So now we can look at all those views straight on and we get the full 3rd-angle viewing arrangement:
Note that the 3rd-angle symbol in the bottom-right of the sheet is slightly different from the 1st-angle symbol. The small end of the cone now points toward the front view circles, and opens away from the front view.
The direction the cone faces is a consequence of rotating the 3D object around the edge of its bounding box that is nearest the camera, instead of the one farthest away.
It is worth noting that you probably will never see all 6 orthogonal views on one drawing sheet. You should see the minimum number of views necessary to define the part, which is usually 3, but it depends on how complex the part is. For third-angle the standard 3 are front, right, and top views. For 1st-angle this means front, left (arranged on the right) and top (arranged below). For totally symmetrical parts, you may only see one or two views.
There might also be section views, auxiliary views, detail views, and so on. For manufacture there will often be more than a dozen separate sheets with various views of a single part to show the geometry as it will be set up at each stage of manufacture.
Drawings have a lot of rules that people can break or bend, as long as we all follow The One Rule: the drawing will clearly communicate everything about how to make the part, even if the designer is on vacation, or passed away 200 years ago.
So I think that is enough on the topic for now, but if you want to test your understanding of this (and you really should make sure you have it dialled) I've made up a 10-question quiz which you can access over at SolidWorks Course Pro, or on the free SolidWorks Accelerator community.
Stay tuned to this page for future topics on CAD design with SolidWorks, as well as selected highlights and tips from the full SCP course. One easy way to stay notified would be to join the community!
- Watch the free webinar and get a large discount on SCP membership, SCP also provides an economical way to access a SolidWorks license, as members qualify for the official student discount.
- or you can apply to join SolidWorks Accelerator for free.
It is a really great community of both learners and experts, and I hope to see you there!
Aryan’s YT Channel has some good videos for reference if you are dealing with drawings. Here is the one dealing with 1st and 3rd–angle.
Wishing you a lovely day
-Jesse Davis
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