spindle speed and feed rate for turning
Lathe turning is a single point operation, most of the time. One "tooth" or one "flute" engages the material, and that cutting point does all the work. Every turning op involves shearing or lifting material from the part, and these shear forces generate intense heat at the cutting tip. The heat being generated, the cutting tool material being used, and whether cutting dry or with flood coolant, all combine to determine SFPM :
sfpm = (rpm x part or cutter diameter) ÷ 3.82
HSS tooling is the least tolerant of heat, and must be run at the lowest SFPM. Somewhere around 100 SFPM is a good place to start. Chip color should be from no color at all, to just the lightest tan color. Go faster, get darker chips, and you've drawn the edge hardness so much that the point becomes blunt, stops cutting, and starts rubbing.
Cobalt tooling allows higher speeds, as cobalt has a much higher red hardness. A popular brand is Cleveland Mo-Max Cobalt:
It's sometimes called M33 or M42 (because of the moly content), and contains about 8% cobalt. When Cleveland patented the process, it was the first successful molybdenum-tungsten high speed steel - now referred to as cobalt. It can be run about 50% faster than plain HSS, and will tolerate chip colors to dark brown without a problem.
Carbide tooling is the next step up, and will run twice as fast as HSS. You can buy ground carbide inserts (which have to be sharpened & resharpened):
You can also buy tools that use carbide inserts:
When these get dull, turn the insert around or flip it over for a fresh edge. Some coated inserts will produce blue chips all day long & show little wear.
As far as setting DOC (depth of cut) and feed, the machine horsepower will limit that. Experiment with different settings to find the ones that work best. Carbide inserts always have recommended settings in the company information.
