Bugger, I just saw this after posting a long PM to Peter
. I always use water soluble oil when cutting ali and alloy steels (I have a high volume pump coolant setup). Usually just use WD40 for hot rolled mild steel and nothing for brass or free cutting mild steel and bronze. I have found kero or thin machine oil is good for cold rolled mild steel both on the lathe and mill. I have also stopped using indexable carbide tooling for a number of materials and job on the lathe as I am getting better results from cobalt tool steel. I have found that the carbide tooling is good for brass, hard alloy steel and cutting and facing aliuminium but is useless for cold rolled mild steel leaving a rough finish whilst the HSS cobalt steel does the lot and you have a choice of profiles via the grinder. My lathe will only run at 2000rpm max and I think the carbide inserts are actually wasted on it. Different story on the mill which can run at much higher speeds producing a good finish on all materials. Here's a few pics of my latest project carved out from 2" 6061T6 round bar. I have placed a 50 cent coin next to the block to give you an idea of scale. The small bolts holding the front and back covers on are 10BA ~ 1.5mm, try drilling and threading those with a tap, nearly drove me insane
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Mark