Hmm, I tired cutting thinner passes each time I had a problem as I thought it would create less heat. Perhaps I need to cut deeper. Chip extraction is obviously key too, but how do you do it well without coolant? I have a reasonable vaccum but a lot of the alu chips are too heavy to extract well that way. It works great for wood :)

What depth do you tend to do got the first pass, Jazz, and what tool do you like to use for general contouring? Do you use a ripper/rougher or a smooth flute?

P.S. Thanks for all your advice chaps!