Like Dave (SillyOldDuffer), I also use neat cutting oil on the mill, from Warco in my case. I have a flood coolant system but use it from an oil can at present as, also like Dave, I find flood coolant ends up being splashed everywhere; I need some guards making to contain the mess onto the table – another job to do on the "to-do" work list! I have also (yet again like Dave!) wondered if I spent wisely buying a flood coolant system, but as it was on a 'special offer' and under ££100 and a few years ago now it's now a case of "oh well…..", money well gone and out the budget now and forgotten!
However, I do find that use of flood coolant/cutting oil is a great help when milling steel both in getting a good finish and getting the swarf out the way plus helping extend tool life, I use HSS tools. Just my experience on my machine.
Chris