Understanding the difference between First Angle and Third Angle Projection can help prevent costly mistakes and is crucial to being a good engineer.
There is a strong chance you will have seen symbols like this on an engineering drawing:
For example, they are usually on the border of a drawing:
But what do these symbols mean?
These symbols are used to show the person looking at the drawing how the views are laid out.
They help the engineer understand what the 2D drawing model would look like in 3D.
When you realise the symbol itself in 3D looks like this:
It becomes a lot easier to understand what is going on.
What is First Angle Projection?
First Angle Projection symbol looks like the following on a drawing:
Let’s imagine the 3D model is orientated as shown above. Then we have the front view on the left, and a side view on the right:
So how have we rotated the model to get from the front view to the side view?
We pushed the front of the model to the right and rear of the model to the left.
This is how model views are laid out on a drawing.
If we were to carry on by placing more views, with the top, side and bottom we would have the following:
What is Third Angle Projection?
Third Angle Projection is similar, however the projection direction is the opposite to First Angle Projection.
To get from the view on the left to the view on the right, we rotate the front of the model to the left and the rear of the model to the right.
Similarly, the opposite is also true – to get from the view on the right to the view on the left, we rotate the left hand side to the front and the right hand side to the rear.
When you now look at an engineering drawing, you will be able to work out how the 3D model looks just by seeing if it is third angle or first angle projection.
Your turn: Are the following views in First or Third Angle Projection?
Now We’d Like to Hear From You
There you have it: a simple explanation between first and third angle projections.
Now we’d like to hear what you have to say:
What type of projection do you use?
It could be for work or for education.
Either way, let us know by leaving a quick comment below.
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4 thoughts on “What Is the Difference between First Angle Projection and Third Angle Projection? (Simple Explanation)”
Surely the first angle projection should have dashed line to indicate the unseeable smaller diameter. This would indicate how the item was viewed. The third angle you would see two solid circles.
Hi Les, thanks for your comment.
The projected angle symbols are used to show how a view is rotated next to (or “projected” from) another view.
In both first angle and third angle projection the tapered solid with the smaller diameter is facing towards us, so the smaller diameter should not be dashed as it isn’t hidden.
If you imagine how the face-on taper rotates to get to the side view, you can see how views will be positioned on a drawing next to each other.
if the diameter of the smaller line on he symbol were dashed as you describe, then by definition the symbol would in fact be indicating third angle.
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