Hi Sanghera,
How's the weather around Ask Me if Needed ?
That is a big question you asked. Basically, your 3d drawings are most likely not ready for direct cutting. This is because your surfaces and /or contours lie exactly on the outline of the object, thereby defining the object.
So starting from that point, you generally would have to "section" your part, to create slices of the model every so and so often. Then, each section is treated as if it were a 2d part, and an offset contour is made, to allow for the diameter/radius of the cutter you plan to use to cut the piece out.
Once you have created these offset contours, and perhaps joined them up, then you have the beginnings of a toolpath. So the toolpath really consists of a table of coordinates describing the distance from the present position, to the end of one of your screen entities that is contingent to it. When it gets there, then it looks for the next endpoint.
There are two ways for the machine to move to an endpoint: a linear straight-line move, or an arc movement. What will be missing from your table of coordinates, and which must be somehow added, is the G codes that will tell your cnc whether the move is linear (G1) or clockwise arc (G2) or counterclockwise arc (G3).
There is also the possibility that some movements will not be cutting movements, but simply Rapid movements to get the tool into position to begin the cut on a new chain of entities. This would be a G0 movement.
So you see, there is quite a bit for a gcode convertor to do, and to do it correctly for 3d work is very difficult to do in simple fashion. That is why we pay from hundreds to thousands of dollars for cadcam programs to help us with the task.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)