Is this an example of what backlash can do?

[Jonathan]

N80X0.000Y0.000F2400.0

Is the F for feed rate and is it too fast...?

Thanks in advance!!!

Yes that's right. 2400mm/min is much too fast for your machine seeing as the x/y will only do 1500. Mach3 will automatically limit the feedrate to 1500, but still if your machine only just manages to rapid at that speed it's no wonder it looses steps with the additional force due to cutting.

I'd set the feedrate to maybe 800mm/min to start with and see how it goes. Be careful though - too low a feedrate and too high a spindle speed will burn the cutter. So check it's not getting too hot...