2D/3D CAD update:
I have used 2D CAD programs for 22 years, and learned manual drawing on the drafting board in school, and as stated before, 2D CAD is very much like having a drafting board on the computer screen.
The toolbar buttons are similar to the old circle, ellipse and triangle templates/tools we used.
I am new to 3D and still struggling greatly with it.
I have yet to produce any significant 3D drawing.
As I try and come to grips with 3D, I have to ask myself what are the differences between 2D and 3D, and why does 3D feel totally different and strange, unlike 2D.
Ultimately the things that I use to build engines in 3D are the same thing I use to build engines in 2D, which is the 2D drawings of front, top, and left side views.
I will use Brian Rupnow as a case study (sorry Brian, but you are one of the HMEM folks who use 3D all the time). You can see that many of Brian's ideas begin as pencil sketches, and then get input into the computer via 3D models, only to be converted back to 2D construction drawings. So it begs the questions, what is so good about the 3D process since it ultimately produces the same old 2D drawings that the 2D program makes, and who should and should not use 3D programs.
Drawing in 2D for me is a "what you see is what you get" type affair. You hold a part in front view and just draw the lines you see. Same for the right side, top, bottom views, etc.
Drawing in 3D is much more like throwing a large chunk of modeling clay up on the tabletop, perhaps in a large rectangular block. As you need features, you either cut things out of the block, or add chunks of clay onto the part.
As you are working on the chunk of clay, you are rotating it around in 3 dimensions, and can look at it from any angle. The trick in 3D when you modify the part is knowing which side to spin the model to, and how to attach and size a part. You can attach a piece to your part not only in the X and Y direction, but in the Z direction also.
The Z component is what gets things confused, since you never have to deal with that in 2D.
Many modelers would benefit from skipping the 3D altogether and just drawing in 2D like the good old days. If you just need some sketches, and don't want to save the world, just draw in 2D.
For the Brian Rupnow's of the world, Brian uses 3D at work anyway, so he already has the knowledge base of the program, and can take advantage of what 3D can do for you.
I have struggled to put into plain words what 3D can do for you.
As I understand it now (which is not too good), in 3D, you sculpt this block of clay, cutting holes here, extruding out flanges and parts here and there, and then having made this 3D thing, you can almost immediately and very easily make the top, bottom, right, left, and isometric views of the object, as well as a section at any point or angle (at least in Solidworks it is easy to do this, I am not sure about other programs). You just sort of point at the 3D model, and then drag and drop windows for the front, top, and side views, sections, etc. and the views just appear like magic.
One big obstacle I have in converting to the 3D mentality is that I tend to think of an engine as one entity, and if you use 3D, you really must draw one part at a time, and then assemble the parts into a complete assembly. When you draw in 2D, you can draw a complete part, or a piece of a part, or half a part, and half of another part, the program does not care.
For 3D, you must draw one shape at a time, and it must be a complete and closed shape. 3D is totally intolerant of any open ends or partial pieces, which is frustrating, since in 2D I often rough out the end of say a connecting rod, and then draw the other end later when I get to the other end of the geometry for that piece.
Changing the dimensions of a part in 2D is simple, you just stretch the part to whatever size you want, and the dimension updates automatically. The downside is that if you change a dimension in 2D on the front view, the other views do not update to that dimension, so you have to change the same dimension in every view.
For 3D, to change a part dimension, you have to know exactly which piece you want to change, and figure out how to access that exact piece in 3-dimension. The good thing is that once you change a part size in 3D, all of the 2D views and sections update automatically.
The other thing I have noticed about learning 3D CAD is that it tends to be so different from 2D that you really need a video tutorial for much of it. 2D is easy to learn just by reading a book. The good thing is there are a number of good video tutorials for 3D on YouTube, as well as at some of the software sites.
I get the same feeling trying to learn 3D that I got when I first went from driving a car to flying a twin beech. In a car, you just turn the wheel whichever way you want to go, and it goes left or right, two pedals, go and stop. A car has a few simple instruments, a speedometer, gas gauge, sometimes a tach. Flying a twin beech with the engines low on the wing and a neutral center of gravity is tricky. It feels like you are driving a car and your steering wheel comes off in your hands, and is attached to the steering column only by a thin rubber band. The steering wheel moves in any direction and rotates as it is moving, and to complicate matters, the two pedals need to be used in conjunction with and coordinated with turning the wheel, but not when the wheel is pushed only forward or back. An aircraft has lots of instruments, and so you get distracted trying to read the instruments, and also to look out the window and watch where you are going.
Gets confusing real fast, and you go into information overload quickly, which is where I am on 3D right now. I have started using Solidworks 2011, and although it is not perfect (I understand the files are not backwards compatible), it is an impressive package. Steep learning curve, but at least it is a stable program and like my poor and abused Grizzly lathe, somewhat tolerant of a new user's blunders. The full Solidworks package does give one the feel of stepping into the cockpit of a modern jetliner. You can't help but gasp at the number of gauges, levers and actuators in a modern jet. Using all the power of all the add-ons in a full blown 3D package (I have the simple basic and least expensive package which does not do simulations, but does do animations) makes me wonder "what the heck have I stepped in, holy cow".
I have newfound respect for the guys who designed the moon rockets and other complex things using a pencil and paper, and who had to do all the 3D visualization in their head.
The only other thing that comes to mind is that CAD systems (2D or 3D) are only a tool, and the real power is in the mind of the person using the software. If you can't conceptualize what you want to try and make in your head, then you can't draw it no matter how powerful the CAD program is. The real power is in the mind of the model builder, but using 2D CAD is akin to having a lathe and knowing how to use it. Using 3D CAD is akin to having a good CNC machine.