Benny,

You haven't stated whether your tool is in climb milling mode or conventional milling mode.

Conventional milling mode will likely have a greater tendency to burn the work if your feedrate is too low. However, if you are climb milling, and your machine has mechanical backlash, or general flimsiness, this could cause rough cutting. If the spindle is flimsy, or inadequately supported, then this can also cause the rough cutting when you feed it heavily (as per normal cutting)

If you are mixing both modes of cutting together, this would make for the worst of both worlds.