I use Fuchs E-cool water soluble oil at 7 % as lubricant. I do not use constant surface speed, your not moving much in x so it doesn't matter. The cutting tool I use is an Iscar threading insert though any higher end indexable insert should be fine. A .005 depth of cut start to finish on coarser threads, reduce d.o.c. as threads get finer. After I make my last pass with the threading tool I re-run my profiling op over the lead in and thread to clean it up, then come back with the threading tool and make two spring passes to chase the threads. Comes out perfect every time. Coolant is everything on alu. and stainless. If your coolant sucks so will your finishes. Rapid tap works well for threading not the biodegradable stuff but the fck mother earth stuff. It'll leave a mess though.