Before running any free downloaded post, run the output through a G-code simulator (like NC Viewer) and then run the program with the feed override at 0% and the spindle off for one full cycle.

Check C:\Program Files\GibbsCAM\Posts\ on your computer. Files are often organized by control manufacturer (e.g., Fanuc, Haas, Mazak).

You can find a if you are looking for a legacy 3-axis Fanuc or Haas generic post from official user groups or your own installation disk. However, if the machine has a rotary axis, a sub-spindle, or high-speed machining logic, pay for a verified post.

GibbsCAM post processors are not plain text like LinuxCNC posts. They are compiled or encrypted depending on your license. However, GibbsPLC (the scripting language) allows user modification.

Without the developer kit, you cannot significantly alter a compiled commercial post. This is why "free" generic posts are often limited.

If you are looking for a free download because you are in a pinch, try using the standard posts that ship with the software.