3d CAD modeling has come so far in such a short time. I remember when got my first taste of 3d modeling back in 1998. It was pretty clunky back then and took a lot of time, but it was so cool it was worth all the effort! In 2000-2002 the usability became a bit better. Fast forward to 2007 and there was a turning point of usability. Not that long ago you had an Engineer do all the design and thinking. The Drafter did all the 3d modeling and created the detailed drawings. The modern Engineer now has be an expert in both domains. We now have these great tools to liberate all of these designs from our overactive imaginations instantly. However, like all technology it usually progresses so fast it makes us forget where things came from and how we used to do things. Let’s slow it down for a minute and talk about how mechanical designs are communicated.
Like it or not we are two dimensional creatures with an amazing three dimensional imagination. If you step back and ignore all of the hype about 3d PDF’s, Multi Axis Machining, compound curve generators, etc., we still only have two hands, two eyes and a flat piece of paper, or a two dimensional computer monitor to work with. It is just much easier for us to sketch our detailed ideas in two dimensions. The skill comes in rotating that mental 3d model in your head and describing the geometric requirements that make your idea work. The goal is to do this so someone else can easily understand it. You can have all the ideas in the world, but if you can’t articulate them in detail you won’t get very far.
In the United States our drafting standard works in what is called “3rd Angle Projection” , and conforms to a specification called ASME Y14.5. You can print out the example below and follow along. Picture the folded up paper cube being a clear box that you can put objects in. It has a front, top, and right view. Cut out the example and hold the “Front View” in your hand. Fold the “Top” and “Right” views away from you. When I refer to a “view” rotate the folded paper so you are looking straight at it. This is also referred to at “Normal to” which means perpendicular to a plane. All of these views are known as “Orographic Projections” or “Projected Views.”
Let’s start with the “Front” view or sometimes called a base view by some CAD programs. The “Front” view is the key every drawing. In “Third Angle Projection” it originates in the third quadrant of the “Cartesian Plain” (yes, this is from math class). This view should contain the most detail about your part. It is the first thing you look for when you pick up a 2d detailed drawing. The Top View is drawn in the second quadrant, the Right View in the third quadrant. The three dimensional view in the example is called an isometric view (1st quadrant) and is the combination of Front, Top, and Right views. Don’t worry too much about the quadrant stuff, I just wanted to show you where it came from (though it will impress your engineer friends). Notice the dotted lines on connecting the features together between views. These are called projection lines. Any time you have a feature in one view you should be able to draw an imaginary line connecting features. These imaginary lines used to be very real and necessary when drafting was a much more manual task. They were either erased from paper or put on a hidden layer in a 2d cad tool. It is all automated for you now with the click of a button. The key is to understanding what the computer is automating for you to create these views. When you get to more advanced parts and drawings this will become even more important.
Now we need to talk about hidden lines and center line. As you get more advanced at flattening out a 3d part in your head into 2d views, you will run into situations where you need to show a hole or pocket in one view. When you rotate to the next view there is nothing to show. You can represent these features with dotted lines. Think of it as X-ray vision showing you what’s inside the part. Lines you can can see with the naked eye are solid, any lines you using your super powers to see are dotted lines. This really helps you and your counterpart visualize the orientation and position of features during any part of the design or manufacturing process. Hole centers are denoted with cross hairs and centerlines as shown in the above image. Centerline are very important to distinguish between pockets and holes when using the hidden line method. Now these hidden lines are optional and usually reserved for critical or problematic features. There will be parts that if you showed every hidden line it would look like a plaid shirt. Imagine you are a superhero and you are using your X-ray vision on a skyscraper to save the damsel in distress. If you saw every pipe and steel girder you would never figure out where the stairs are and where all the bad guys were amongst all that confusion. In short, show what is important and save the girl, puppy, or kitten you have in your own imaginary scenario.
I know what you’re thinking: “god this is boring! Doesn’t the computer do this for me now?” When drawing, ask yourself if someone else could create your part without talking to you. This is more about building your design language so you can communicate with others in this field of work. If you can’t learn to speak a language in a foreign country you won’t get very far. The best way to learn this skill is to pick up relatively square things around your house or shop and draw them. The cool part is you literally have the answer in your hands. No one is grading you so keep at it and you’ll get it! Turn the object to the side you want to draw an ask yourself does the picture look like real thing? Once you get the hang of it, conveying your ideas to one another and approaching 3d modeling will become second nature.
This is a skill that everyone can learn. You don’t have to be an Engineer, Drafter, or a Machinist with 20 years of experience under your belt. All you need is some paper, a pencil, your imagination, and a little practice. This article may be review for some, and brand new to others. If it’s review, find a young kid or a peer to teach it to. If it’s brand new, seek out people who do this stuff and ask lots of questions. Be open to learning as much as you can with each interaction. We have to pass on these skills to each generation and not just rely on the software to do it for us. Heck, if you think the computer does everything for us then what does it do for the poor software engineers? In another article I will explain a few other types of detail views and some insight as to how parts are dimensioned properly. Leave a comment so I can get a sense of where everyone is at skill wise. Have fun, and never stop drawing!