2 1/2 D CAD - 2 1/2 D CAD is 2D CAD with the added ability to designate multiple depths as long as the depths are planar. That is to say the depth is the same over a flat area and it does not vary in that area. You can't, for instance draw a sphere in 2D CAD. You could approximate a sphere with lots of tiny circular concentric steps. This would be fairly time consuming.
2 1/2 D CAD is useful for many mechanical parts that need 3D characteristics but that don't need curved or angular design features. Also with the use of 2 1/2 D CAD and certain curved tooling you can get parts with rounded or chamfered edges and inside corners. These features just won't be evident on the CAD drawing.
3D CAD - These programs allow you to render parts with complex shapes & surfaces. But, the ability to render many shapes is greatly dependant on the abilities of the program. Most programs allow the construction of cubes, cylinders, and 3D polygons. Differences begin to appear when you need to merge shapes, resize shapes, make fillets, and blend surfaces together.
These programs also allow you to view your shapes from different angles. They typically have rendering features that allow you to shade and color the shapes. Depending on the sophistication of the program, your skill, and time you can get drawing that rival 3D graphics only packages.
There are a group of programs called solid modeling programs too. These are like 3D CAD programs but they have multiple special features that allow better rendering and manipulation of 3D objects.
As solid modelers and 3D cad programs try to build in each others feature sets, they are becoming more and more alike.
So, a lot of people who are new to CNC are trying to get a grip on how this all works. You start with an idea for a part, put it in a cad drawing, convert that to g-code, feed that to the machine, put some stock in the machine, line it all up, start the machine and your part gets cut.
That is A LOT of technology in action.
So....lets start with a basic diagram of the flow.
CAD - Computer Aided Design
These are electronic drafting programs. There are lots of brand names. Some are listed below. This family of programs allows you to draw your parts on your personal computer (PC).
There are three kinds of CAD programs. Well, there are more than that, but lets focus on these ones. 2D, 2 1/2 D, and 3D. This will be a repetitive concept as we move through the different software and operations.
2D - 2D CAD allows you to draw flat drawings. This is like drawing a picture of your car from one side on a plain piece of paper. All you get is a profile. This kind of drawing is totally acceptable for parts that are a uniform thickness and have a shape that is cut out of a flat piece of material. If you look around you there are a lot of things made up of parts like this.
