HSS provides a better finish at low speeds, on a light machine. Carbide, and coated carbide, work better at higher speeds and are mandatory for some of the tougher alloys. The truth is, nobody grinds HSS bits much anymore. but if they do, they can produce a tool which is sharper and cuts with a lower chip load than many of the carbide inserts. HSS is not cost effective for modern production facilities, but is still useful in special applications. I use HSS when threading inside receivers. Here, my chicken- heart induces me to use slower speeds and the HSS produces a nicer finish. GD
