Orthographic Drawing Techniques in AutoCAD
Putting your skills to use.
So far in this level you have been learning the basic 2D AutoCAD commands. What you learned in this level will be a very large part of what you use in your daily drafting. This tutorial isn’t going to teach commands, but will instead show a common technique that is used a lot in ‘Mechanical” drafting. It will also ask you to think about what you are drawing, and how it needs to be represented.
Mechanical drafting is a field within the drafting world. In simple terms, it is used to describe the methods for drafting and designing machines, assemblies and in a nut shell, the ‘parts’ that used in everything from a fork to a Formula 1 race car. It doesn’t include anything that involves buildings and structures (Architectural & Structural drafting) or landscapes and roads (Civil drafting and engineering).
Now just because you are dreaming of becoming an Architect, it doesn’t mean that you should skip this tutorial. In fact, you will likely need to use these concepts or read diagrams related to this subject. So read on!
What is Orthographic Projection?
If you look at the image below, you will see a drawing for a part. It shows the object with a top view, a front view and a side view. You’ll also see an Isometric view that is sometimes used to give a more visual look. This tutorial won’t cover Isometric drafting as it is shown in Tutorial 3-2. Save your drawings that you do in this exercise for more practice in that lesson.
The reason that this method is used is that you can take a designed part, draw it, dimension it and then give all the needed information to the manufacturer.
In some cases only 2 views are needed, but for anything more than a simple part, 3 or more views are needed. Very complex parts will need 6 or more.
There are 2 methods of deciding what views are used and where they are placed in the drawing. I’ll borrow some info from Wikipediato show this:
Ok – that was some fun theory – thank for reading it. One last bit of info before we get back to CAD stuff. Since there are 2 kinds of standards, how do you know which is which when you have a drawing in front of you? There is a standard symbol that is used in the title block to indicate which method was used.
This symbol shows a simple cone and displays the projection. Think about which symbol represents which method, then move your mouse over the images to see if you were correct.
Because I am in North America and was trained to use the “Third Angle Projection” method, that is what I will show in this tutorial. The techniques for drawing are the same, it’s just a matter of which direction you ‘project’ or draw the lines.
Here’s a short video for you that explains these concept visually.
Drawing 3 View Orthographic Projection
For these exercises, we’ll start by looking at an Isometric drawing of an object and then draw the Front, Side and Top views using the dimensions we’re given. In the workplace, you might find that you are given a part to measure and then draw, or you might be designing the part yourself.
Here’s the part that we’ll draw in this tutorial:
This is a very simple example to get you used to the concepts. You’ll have more practice exercises at the bottom.
Ok, the first question that you’ll ask yourself, is “Where do I start?”. I recommend that you start where you have the most information. This will sometimes be the front or the top – it depends upon each drawing. In this case, I will start with the front and draw it.
You don’t need to worry about dimensioning it at this point – wait until you have all of your views drawn. Ok, this should have been easy enough, so now you can start drawing the top view.
To draw the top, you need to ‘project’ the lines up. Draw lines up from the main points in your front view. Make sure you have your Osnaps on (include “Quadrant”).
Now that you have the vertical lines, draw the horizontal lines. Make sure you leave enough room to draw the width (via OFFSET) and space between the views.
Now you almost have 2 views drawn. Trim the lines so that you are left with just the lines you need.
Stop and check to make sure that you didn’t forget any lines. It’s very easy to miss some.
Now it’s time to jump ahead a little and take a side trip. Read Tutorials 4-3 to learn about Linetypes, because you will need them here. After reading the tutorial, return to your drawing and load the Hidden and Center linetypes. These are needed to add more information in your drawing.
If all went well, you should be able to load the linetypes and scale them (LTS with a value of 10 or 12) to fit with your drawing.
What you see above is the completed Top and Front views. Do you understand why there are “Hidden” lines? They are there to indicate that the hole (circle) is drilled right through the block. Where would the lines be in the hole was only drilled half way through? The center lines are used to show the the hole and the arc have the same center point. These are both common and standard CAD methods and you need to understand them.
One more view to draw. This will be the side/right view. Can you picture it yet?
To get started on the side view, you have to establish where it will be placed in the drawing. In this example and using the 3rd Angle projection, it will be shown to the right of the front view. For exact placement, you need to draw more projection lines.
What you see in the image above is that I established the top right corner of my front view by projecting 2 lines. Then I drew a 45 degree line up from the corner.
Now I can start projecting lines from my top view to create the side view. The line that is indicated by the ‘Project Down’ leader will be the left side of my Right Side View. I would project another from the other side of the top view and that would establish the width of the right side. Also note that by using this technique the top and side views are the same distance from the front view.
From there I just need to project to the right from my front view.
Almost there. Now you just need to trim up some lines and change the linetype for the hidden lines. Final goal is to draw this:
Once you have all of your lines, your center lines and your hidden lines, you are ready to dimension and add any notes that are needed.
Think about what commands you used in this tutorial. You used LINE, CIRCLE, OFFSET & TRIM. You also use Layers and then learned about Linetypes. What this shows is that you don’t need to use a lot of commands, but it’s your knowledge of how those commands works that makes your reputation as a CAD user.
Extra Practice: Draw the missing Right Side View and the other views (except Isometric) for this drawing.
Extra Practice: Here is a scan from an old (1919) drafting book that I found on Google Books. This image has 4 separate exercise to keep you busy. Draw what you are given, and then draw the missing view.
Here’s a video that shows how to construct a basic Orthographic Projection drawing.
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