I don't consider myself to be a "machinist". Rather I am someone learning by experimenting to see what works. Or does not work as the case may be. What follows then, is as a result of my experimenting and may not be applicable to others.
For steel I use Neatcut which I obtained from Warco some years ago. I did some experimental deep & high rate cutting using tools made from old files: these produced lots of smoke, but the tools did work. However, as a matter of course, I do prefer light cuts so much less smoke.
I also have some Rocol fluid dilutable 1:1 with water. It makes a mess, and leaves a green sticky mess behind. As a result I now only use it for parting off, mainly because it will fill the cut.
For aluminium I use a concoction of oily dregs & paraffin. Proportions, I have no idea but I suspect probably 1:1. It does give a reasonable finish to the ali although I suspect pure paraffin would be just as good.
To apply the fluids I use a small paintbrush dipped into a small container of whatever fluid I'm using. Sometimes, such as parting off, I use a small plastic bottle supplied, I think, by Millers. These have a flexible spout with a sealing end and can inject the fluid into a hole up say 50mm deep. Unfortunately, the Rocal fluid causes the sealing end to seize up and block, so I have had to make a new tube out of brass. Ok, I've lost the flexibility, but at least I can still get the fluid into the cut.
Just to expand slightly: I use Trefolex for threading, and ordinary (presumably) engine oil dregs both on my hacksaw blades (makes hacksawing much easier) and on the drilling machine which does make for easier drilling albeit with a little bit of smoke.
One snag with the Trefolex is that the oily liquid in which the solid compounds are presumably suspended has separated out such that I now have to dip well down to get the solids. Is there any way of recombining the two parts?
Cheers,
Peter G. Shaw