Hi guys,
Sorry for the confusion. File Save As will save the drawing file only.
To generate gcode, use the
CAM->Generate Gcode File menu option, or right click on machining on the tree in the left and select 'Create GCode File'.
This should prompt you for the location and name of the gcode file.
You can also right click on individual machine operations in the tree and select 'Create GCode File'. This will create a gcode file for just that one machine operation.
I hope this helps!
edit: Reading again, no CamBam does not automatically append an extension to gcode filename. It may suggest a default name with a .nc extension but you can overwrite this.