usually any CAM software contains data about its post processor
i.e help or something
you can modify the post processor of any software according to the codes your machine understands and this is always not a very difficult stuff

Hi,

We have found that for simple 3 axis machining, it is sufficient to modify an existing post to suit our needs. generic posts are usually supplied with CAM software.
However, for more complex and specialised machining, (eg 5 axis maching of complex surfaces), we have found that writing our own posts using Visual Basic gives us the most control over the tool. Once you have a CL (cutter location) or APT file you can write your own post, which works with your machines in the way you want it to.

thanks a lot Jmark you helped us so much reaching the point but unfortunately
airuno is askink for absolutely different story ,
he is a student in the first degree in the university of agriculture  and wants to learn the early beginings of G codes and post processors I doubt that he knows what a milling machine is .
but anyway thanks a lot

Thanks for your help guys, but I am looking for an information about WRITING new post, not modifying existing one. I am making a simple application in VB which will be able to convert a tool path into G codes and vice versa. I can do hard coding to suit my machines, but I would like to know how commercial CAM packages do post-processing. This application is meant to be for CNC lathes with live tooling at this stage.

Thank you

airuno,

Here is how mastercam works:
An NCI file is generated by the software which contains tool, cycle and cutter location information. The file is set out as follows:
CYCLE
PARAMETERS

For example, a rapid move would be defined by the following 2 lines:
0
10.5 3.8 1 0
In this example, the first line contains a zero which defines that the following parameters are for a rapid move. The second line contains the rapid move parameters: x position, z position, cutter comp, move angle.

The post processor merely needs to have a databse of all the cycle numbers and what parameters each one requires. Converting this into G-code is then straightforward.

Thank you jmarc, this was the information I was looking for. It is all clear now.