A lot of drawings are in “first-angle” projection, and unless you know what that means and what to look for you can end up shooting yourself in the foot when trying to model from them. This is a basic skill thatmany people miss when starting out learning CAD on their own.
Sometimes looking at drawings is hard. This is the first of two blog posts (the second post is here) that aim to help you sort this out, and you can find links at the end to a 10-question quiz available on our community platforms.
You can manage an intuitive understanding of how to look at the drawings we are given to model from without ever studying the topic; stare at the lines for long enough and the brain might eventually work out the answer auto-magically! That is part of our natural human ability to work mentally with 3D objects.
And we CAD-people practice reading drawings all the time, so even a beginner in CAD quickly becomes much better than the average person at seeing the real object from the lines on the page. It mostly just takes practice.
On the other hand, complicated or strange shapes are genuinely difficult to translate from 2D into 3D. Too often, the drawing just looks impossible, and you can feel your mind bending in half trying to visualize it.
But there is a system! CAD modelers and designers don’t just depend on vibes when working with drawings. Engineering drawings are made with either first-angle or third-angle projection systems, and knowing which is which will help you easily see the true shape in your head, as well as reduce your blood-pressure. Etch the basics of these two systems into your mind and open a door to drawing enlightenment!
This post will explore what first-angle is and how it is created, and what to be careful of when reading the drawing. Reading this will also set you up to understand the next post on third-angle projections, which are generally easier to visualize and may be more common depending on your region of the world.
Understanding what shape the drawing lines make starts first with understanding how the model made the lines; we put our model in a cube and place it on our drawing table (first-angle), or inside our drawing table (third-angle). Then, we ‘roll’ the cube around on its edges that meet the table to get our different views.
So let’s start creating a 1st-angle drawing.
First, let’s establish the basic views. Here is a ‘front view’ drawing.
It is obvious that this should be the front view of this friendly guy. His face is towards us, and this view shows us the most characteristic and descriptive shape of the scene.
Then, we can easily imagine the “Back view”
These two views are intuitive enough, but there is a little detail here that will be confusing: the ‘front’ of the object in the drawing is exactly opposite to the ‘front’ of the viewer of the drawing. For this view that is no problem, but it will cause some mental sweat in the future.
For example, we all know that the man is lifting his right hand even if it is drawn on the left side of the paper, because this is just like what we see meeting a person in real life. Later we will see that this means the ‘right view’ will show us the man’s left side… but more on that later.
“Top” and “Bottom” views are also intuitive.
With these 4 views now complete, we can arrange them on a single page, and we come to a rule of drawings that you should try to follow at all times: different views of the same object must be aligned! Top and bottom views must be exactly vertical above or below the front view.
A back view could actually be either vertical or horizontal with the front view. Because it is flipped a full 180 degrees, and the back view could actually be anywhere. However, its orientation would change; it would need to be aligned to the front view across a mirror line between them. Here are five back views:
If your drawings are not aligned, your professor will deduct marks, the machine shop people will mock you, and your breath will smell bad. Align your views!
In fact, SolidWorks will more or less force your views on a drawing to be aligned, and if you want to un-align them it is not easy to do.
Angled views should be placed at the exact angle of the plane they are projecting to (an “Auxiliary View” in SolidWorks), but we often use special symbols and break-out views for this, mostly to save space on the page, or make the rotation of the view more reasonable.
So far we haven’t talked about side views though. A side view must be horizontally to the left or right side of the front view, and never above or below, or in a random location. However, which side can be confusing, and that is where we need to understand first-angle and third-angle.
Remember how I talked about “rolling” a cube with our model in it at the beginning? Well let’s get rollin’!
Look at a perspective sketch of our friendly little guy in the chair. We also place him in a glass cube to let him know that escape is hopeless, and put his back against a wall.
We cast straight parallel lines from a very-distant camera in front of the man, and trace his shadow on the wall we will get the front view of the drawing.
This arrangement of model and drawing plane, with the 3D model in front of the drawing plane, and the projection going away from the viewer onto that plane, is first-angle projection.
For now we will work in 1st-angle, but don’t worry much about that at this point. Just remember that is the angle we are ‘in’ as we create the drawings.
The ‘wall’ in this case is actually the flat table-top of our drawing board. So let’s place the man lying on his back, staring at the sky. Poor guy!
Tip the cube over one edge to put him upright again, so he sits on the tabletop normally. Then we do the same trick with lines and shadows, and the drawing plane will have a top view on it.
He is getting too comfortable sitting upright, so roll the cube to tip him on his head! This will project the bottom view, as we look down on him upside-down.
Great! We have three views, but if we look at at the results we have on the drawing plane so far you might notice this:
The ‘top’ view of the model being drawn on the lower part of the page, and the ‘bottom’ view being drawn above, is one of the strange/stupid/quirky/frustrating things about 1st-angle projections.
The same thing happens for left and right views too, but before that a little word about what ‘left’ and ‘right’ mean…
Remember that I said the ‘right’ view would show the man’s left side? Well here is the reason: the right view is ‘camera right’ and not ‘object right.’
Think about the drawing as a picture that you are taking with a camera. After you snap a pic for the front view you will walk around to one side to get the next view.
Do you walk to the right (to the left from model-man’s view)? Then your next view is the right view. If you walk to the left (the man’s right side), it will be the left view.
We might try to solve this by rotating the model all the way around 180 degrees. So then, the left side shows up in the left view, but we see the back side in the front view! This is just the way it works, and there is no way around it. It’s almost a philosophical problem; the viewer and the object must always face each other, so something must get flipped.
The convention around the world, and throughout the history of engineering is that front, back, top, and bottom should be ‘proper’ and left and right get flipped. It is the best compromise, and just something you need to get used to.
So, knowing that, let’s roll our cube twice more to get the side views, and roll once again to get the back view:
This reveals all six views of the model in first-angle projection, and we see the terrible reality:
In first-angle drawings, the bottom is on the top, and the top on the bottom, the right is on the left and the left is on the right!! Why would we ever draw something like this?? Doesn’t this lead to confusion when making the parts??
Well, yes. Yes it does cause confusion. This is why we have third-angle, which we will talk about in a blog post coming soon.
By the way, if you have always wondered (or hated!) that SolidWorks uses the Y-up orientation instead of the modern Z-up, this is why! The software comes from France which is one of the oldest engineering communities in the world, and the ‘front’ plane being XY is another vestige of the same drawing-table perspective of modelling that existed in the past. You also see it if you choose the 4-viewport mode for your graphics window, which SolidWorks lays out like a 1st-angle drawing.
Here is a model of the little symbol you see in the bottom corner of the drawing above. The symbol shows the front view of a truncated cone, as well as one side view (usually the left view) that shows how the cone was 'tipped over' one of it's rear edges. The image below shows that cone in all of it's possible tipped-over orientations, along with drawings it projects behind it.
Visualising a drawing requires us to ‘roll the cube’ in our mind’s eye, but it isn’t clear whether the front or back edge of the cube will become the axis for that rotation (well, if the drawing says first angle then it is clear, but it’s still unintuitive), and even if we know the rules making mistakes is still easy if another way makes more natural sense in our brains.
To understand why first-angle even exists, think back hundreds of years. Back then, engineers were people with amazing moustaches (I think even the lady engineers were required to have large moustaches!) and a penchant for rigorous systems of knowledge. They cooked up this system of folding and projecting planes to intersect imaginary geometry with real-life drawing planes that is consistent and unbreakable. The fact that they invented this robust system of recording and sharing complex 3D designs on flat paper is amazingly impressive!
However, not a single one of those early designers had a computer monitor or a television. If you gave one of them a 3D object to draw orthographic views of, they would naturally place the object upon their table, draw what they saw while looking down on it, and then flip the object over one of its edges, and draw that view - just the same way that we did in the first-angle method above. In an analogue world and at the dawn of engineering graphics, first-angle was simply the natural way to draw things.
Even though creating a drawing on paper back in the old days was nothing like using a magical glass-box computer monitor, creating a real part from a paper drawing was exactly like looking at a monitor, with the object ‘inside’ the drawing. That is what 3rd-angle does, with the drawing plane 'in front' of the model geometry:
If you didn’t make the first drawing from the object itself, 1st-angle is kind of backwards; you have to be taught how it works. Kids drawing spaceships from imagination tend to draw in 3rd-angle (source: that is what I did, and it was actually a flying motorcycle). In imagination, we tend to tumble the object in our head, and then we place the drawing between us and the object. There is a natural ‘orbit camera’ in our head, and it tends to spit out 3rd-angle arrangements when asked to make an aligned drawing.
However, as hundreds and then thousands of drawings in 1st-angle started to pile up over the early days of formal engineering drawing, it became by default the ‘right’ way. I am sure that its drawbacks soon became apparent. Fabricators, as is still true today, may have been less educated than the designers, and we can easily imagine several parts coming out of the factory backwards or upside down. I am no historian, but I am sure that as engineering grew as an academic field more and more formal research into 3D transformations and projections took place, and resulted in the system of 3rd-angle being proposed as more intuitive and practical.
The problem was, and still is, that 1st-angle was already established in existing designs and in engineers’ minds. To be fair, it is a perfectly good system if you can do the mental gymnastics. Therefore first-angle drafting still exists, especially in firms based in or influenced by European engineering.
The symbol that determines a first-angle drawing might not be on the drawing. Some drafting standards name a preferred projection and it is assumed to be correct, for example JIS uses third-angle, and ISO uses first. Drawings done in either of these standards are unlikely to have the symbol in the title block.
You will more often see this symbol if you are in an American company that has to cooperate with European firms, because trans-Atlantic mistakes have caused much hair-pulling and gnashing of teeth in the past.
The symbol on the drawing will have any one of the four side views, but usually it will be the left view (which is placed to the right!), and the key point is that the angle of the cone will open towards the front view if it is in first angle (i.e. it will ‘point away’).
Third-angle drawings use similar symbols, but the angle of the cone will close toward the front view.
We will explore third-angle in the next post, which I hope you are keen to read!
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.
These blog posts and much, much more can be discussed on our SolidWorks Course Pro community where Aryan Fallahi and his merry band provide support and methodical curriculum for those working towards SolidWorks certification and mastery. Watch the free webinar today to learn more, and participants of the webinar qualify for a big discount on membership if you decide to sign up. SCP also provides an economical way to access a SolidWorks license, as members qualify for the official student discount. It is a really great community of both learners and experts, and I hope to see you there!
For those who just want to put a toe in instead, we run a small free community called SolidWorks Accelerator - with these new regular blogs and access to the related quizzes and discussions we hope to expand SA beyond its previous role as a sampler for SCP, so if you are just starting out and wondering where to start your learning process, apply to join SolidWorks Accelerator for free. Come and try the quiz for these posts on 1st- and 3rd-angle and see if you've really figured it out after all.
Hope you are well and all your contours manifold.
CLICK HERE to continue to the next post, on third-angle projections
-Jesse Davis
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