Ok thanks guys. I will give reducing the spindle speed etc a try tonight then. Will this reduce the furring on the edges? At the moment when i am cutting it is producing fine dust so, going on what you have said, i have my speed to high. Just for the record my machine is the Heiz S1000 using a Kress 1050w. Anyway, will give it a go and put the results on here.

PS my local builders merchants did give me funny looks when i queried the make of MDF!