Machining Fundamentals, Materials, and Cutting Tools
Speed, feed, and tool geometry
Cutting speed (SFM or m/min) is surface speed; feed is expressed per revolution, per tooth, or per minute. The core relationships are RPM = (3.82 × SFM) ÷ diameter in inches, and feed rate = RPM × number of teeth × chip load. Depth of cut and radial engagement drive force and heat. Chip load per tooth must stay above a minimum to avoid rubbing and work hardening, especially in stainless and superalloys.
Tool materials escalate in hot hardness: HSS, cobalt HSS, carbide (coated and uncoated), cermet, ceramic, CBN, and polycrystalline diamond. Coatings such as TiN, TiCN, and TiAlN improve wear resistance and thermal barrier behavior. Understand rake and relief angles, helix, corner radius, and the difference between climb and conventional milling. Insert and toolholder identification uses ANSI/ISO codes.
Materials
Know machinability families: aluminum (fast, gummy, needs sharp geometry and coolant), carbon and alloy steels, stainless (work hardening, poor thermal conductivity), cast iron (abrasive, generates dust), titanium (low speed, high heat, never let the tool rub), nickel superalloys, and plastics (melting, chip re-welding). Recognize built-up edge, flank and crater wear, chatter, and the standard wear criteria.
Traps
Questions mix units, confuse feed per tooth with feed per revolution, or assume carbide and HSS use the same SFM. Another trap is diagnosing chatter as a speed problem when rigidity or tool overhang is the cause.
Rule of thumb and worked example
1/2 in carbide end mill, 3 flutes, aluminum at 600 SFM, 0.002 in/tooth: RPM = 3.82 × 600 ÷ 0.5 ≈ 4584; feed = 4584 × 3 × 0.002 ≈ 27.5 in/min.