Not sure what problems you have seen with Mach3 and Lathes but really I dont think there are any.
Please dont take offense if I am missunderstanding but from your reply I am not sure if you understand the diference between Mach and CAM and for that matter CAD programmes.
Mach is the controller, it does all the calculations and sends signals to your motors etc to make them do what the Gcode is asking for. There are also wizards in Mach which will produce Gcode for you, these include wizards for threading, taper turning, radius turning etc. You just have to enter dimensions into the wizard and the Gcode will be produced.
LazyCAM which is bundled with Mach is a CAM programme, you need to import a drawing into a CAM programme and it will produce the Gcode for you which you then give to Mach to control the motors, spindle etc.
SolidCAM, MasterCAM etc are also CAM programmes.
To produce a drawing to import into the CAM programme you will need a CAD programme, examples of which are TurboCAD, AutoCAD and also there are 3D modelling programmes such as SolidWorks, Rhino etc.
Once again if I have misinterpreted your understanding please dont take offense.
Hood