MCAD Modeling Methods-Transitioning from 2D to 3D1 Sep, 2006 By: IDSA ,Mike Hudspeth
The benefits of switching to 3D far outweigh what 2D offers.
In the early 2D days of CAD, when that acronym meant computer-aided drafting, not design, it helped to have an artistic eye. If you didn't have an artistic person at the computer, your drawings didn't turn out that well. I started out drafting, and fortunately I've always had an affinity for 3D sculpture and drawing. In short, I can see and imagine 3D space. Why was that important? Because drawing orthographic projection requires the ability to imagine what the object looks like from different angles. If you worked from actual parts or a model of your design, the process was much easier. But in my experience, drawings were necessary long before such parts or models were available.
In the Early Days
The first really big player in CAD was Autodesk's AutoCAD, still the 800lb gorilla of the industry. With AutoCAD, all of your 2D drawing requirements were easily met. You could draw anything you wanted, write LISP files to make your job easier and incorporate third-party programs to expand your capability. What more could you ask for?
Snap to It
One area of improvement was line and arc termination points. You might know these better as snaps. They allow you to designate an exact location to snap to based on things such as line endpoints, midpoints and arc centers. In the old drafting board days, a line ended pretty much where it looked like it ended. You needed no more precision than that. Snaps allow you to close an area exactly to many decimal places. I worked at a couple of different companies where this capability was little appreciated, if known at all. Many times I've worked on drawings where if you zoom closely enough you see lines ending out in space, crossing or ending just short of an intersection. I'll show why that's important in the "Snap to It".
But as AutoCAD was gaining in market presence and popularity, some people wanted to go further, into 3D. AutoCAD is a superior 2D product, but it has never done 3D very well. It has rudimentary capabilities, but no company I've ever talked to has used it for 3D design. In fact, Autodesk developed products such as Mechanical Desktop and Inventor to take care of this problem.
But why is 3D important? Why should a company that is satisfied with 2D drawings invest the time and money to transition from 2D to 3D?
Why Do It?
I'll admit that this column may sound like a rehash of some of my recent ones that discuss benefits derived from 3D models. But some people still haven't heard the message. 3D is better than 2D for products that occupy 3D space. Granted, if all you produce are 2D products like labels, bandages and gauze pads, you aren't likely to see much advantage to making the jump to 3D (figure 2). But for the rest of us whose parts occupy space along the z axis, 3D makes a whole lot of sense.
Figure 2. Some products don't require 3D models, but most designs benefit from 3D geometry.
There's a big difference between drawing a part and modeling it. When you draw a part, you basically depict one static view of it. When you model a part, you build a 3D representation of it. That difference is huge. If you are designing a hand drill, you can draw one side but are left to imagine what the other sides look like. It's like seeing something on TV. If the camera doesn't go behind something, you don't know what's there. (Remember the mock-up town in Blazing Saddles?)
When you model something in 3D space, you know everything about that model intimately. You can rotate it in space and look at it from all sides. You are far more familiar with it than you are with a 2D drawing, no matter how detailed. You'll attain a situational awareness that different static views can't adequately express. And what that situational awareness can do is show you errors that you didn't know you had. By rotating and zooming on a model, you can see where things don't match the way you think they should, and then you can fix them before any prototypes are made. You'll save a lot of time and money—your ROI (return on investment) will start to look pretty good.
So how do you go from 2D drawings to 3D models? There are far too many ways for me to fully explain here, but in a nutshell you have to model them. There's no automatic way of taking a 2D drawing and popping out 3D models. The software isn't quite there yet, but some tools make modeling far easier than it used to be.
Take Solid Edge, for instance. You can import an AutoCAD drawing into Solid Edge and use the 2D geometry to sweep new solids. Just identify which view is the front, right and top and then which curves are what profile and away you go, sweeping and subtracting until you have a fully parametric solid model that you can really use (figure 3). It's exciting stuff!
Figure 3. Programs such as Solid Edge from UGS provide all sorts of capabilities to take 2D drawings and build 3D models.
Okay, you have a 3D model of your part. What do you do with it? Even in our supposedly paperless society, you'll need a drawing. Drafting is another area in which your ROI is going to look great. No longer will you fear inaccuracy. Each view on the drawing will be pulled directly from the 3D model. All you need do is tell the software what view to put where, and it plops the appropriate geometry on the drawing. All that's left for you to do is add dimensions, and even that can be done automatically if you've set everything up right. Easy view creation, accuracy to several decimal places—what more could you want?
Believe it or not, 3D models can do even more tasks that 2D can't touch. Downstream applications can use the 3D geometry to generate all kinds of things that you and others will find invaluable. Everybody likes pretty pictures (figure 4). You need them to show to clients or to sell upper management on your designs. 3D models can be used to generate those images, and in seconds. You won't need the services of a painter or sketch artist. You'll be able to do as good a job your desk, and in a fraction of the time.
Figure 4. Short of hiring an artist, you probably won t ever be able to generate images like this ATV and building with a 2D system. Most 3D modelers can provide at least medium-quality output.
Another downstream application of 3D models is RP (rapid prototyping). You can send a file to an RP vendor and within a few days, sometimes a few hours, you can get back an actual physical model of your design. Some RP models even can be used for testing. Try that with a 2D drawing.
3D models also can be used for design analysis in a number of powerful ways. With everything from finite-element analysis to mold-flow simulations available at the touch of a button, you can test your models with results that closely match real-world testing. In this way, you can find out if your design will stand up to the forces that you intend to apply to it and, if not, how and where it will fail. Empirical testing of this type would require multiple prototypes to be made and destroyed—each costing hundreds if not thousands of dollars. And that's not even considering the timeline.
3D modeling also allows you to use CAM (computer-aided manufacturing). CAM mills, lathes and other tools can import a mathematically accurate 3D model to cut prototypes or tooling. Have you ever had a shape on a part that was so complex that it was difficult to dimension on a drawing? That's not a problem with a 3D model and a CAM tool.
The real advantage of 3D modeling over 2D drawing is in the inherent capture and presentation of intelligence. A drawing can and should present every aspect of a design, but it can never hope to do so in as intuitive and flowing a way as a 3D model can.
ROI evaluates more than money. It also considers effort and value down the road, the potential that your designs hold to be used and reused. 3D modeling is the clear winner over 2D drawing in every way. If you are on the fence about which way to go, look closely at 3D modeling. Once you try it, you'll never go back.
Mike Hudspeth, IDSA, is an industrial designer, artist and author based in St. Louis, Missouri.
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