Reference

Machining glossary.

The speeds-and-feeds and cutting-tool terms that actually matter on the floor — defined in plain language, with links to the tools and guides behind them.

Ball End Mill: A cutter with a full hemispherical end, used for 3-D contouring of cavities and cores. Note the effective cutting diameter shrinks near the tip, so surface speed must be compensated on shallow cuts.
Built-Up Edge (BUE): Workpiece material that welds to the cutting edge in gummy materials, then breaks off taking coating or carbide with it — ruining finish. Beaten with coolant, the right coating, fewer flutes, and a real chip load. Fix chip welding →
Carbide Grade: Tungsten-carbide substrate defined by grain size and cobalt content. Finer grain and the right cobalt % trade toughness against hardness — RobbJack matches the grade (and coating) to the material and operation.
Chatter: Self-feeding vibration between the tool, cut, and machine that leaves a rippled finish and chips the edge. Fixed by rigidity (shorter tools, better fixturing) and, in aluminum, RobbJack's Mirror Edge geometry. Chatter control →
Chip Load (per tooth): The thickness of material each flute removes per revolution (CLPT). It's the single most important feed parameter — too light causes rubbing and heat, too heavy chips the edge. Chip load scales with tool diameter. Machining formulas →
Chip Thinning: At light radial widths of cut, the actual chip is thinner than the programmed feed per tooth — so you must feed faster to keep a real chip forming. Ignoring it causes rubbing and premature wear at low stepovers.
Climb Milling: The cutter rotation and feed move in the same direction, so each flute starts with a thick chip and thins to zero. It leaves a better finish, generates less heat, and is preferred on rigid CNC machines.
Conventional Milling: The opposite of climb — the chip starts thin and thickens, which rubs at entry and builds heat. Used on older or less rigid machines with backlash, but generally inferior for finish and tool life.
Corner Radius: A rounded corner instead of a sharp one. It spreads cutting load over an arc, dramatically strengthening the most fragile point of an end mill, improving floor finish, and resisting chipping.
Depth of Cut (DOC): Axial depth — how deep the tool engages along its length (Z). Deeper passes remove more per pass but raise cutting force and heat. High-performance tools like the AL3 take very deep single passes without chatter.
Feed Rate (IPM): How fast the table advances, in inches per minute: RPM × chip load per tooth × number of flutes. Feed too slow and the edge rubs instead of cuts; too fast and it overloads. Speeds & Feeds calculator →
Flutes: The cutting edges and the gullets between them. Fewer flutes (2–3) give big chip clearance for gummy materials like aluminum; more flutes (5+) raise feed rate and finish in steels and alloys where chips are smaller.
Helix Angle: The angle of the flute's spiral. Higher helix shears more cleanly and evacuates chips upward (great in aluminum); lower helix is stronger for hard or interrupted cuts. Variable helix breaks up vibration to fight chatter.
Metal Removal Rate (MRR): Cubic inches of material removed per minute: width of cut × depth of cut × feed rate. The headline productivity number — RobbJack tooling is engineered to maximize it without sacrificing finish or tool life. Tooling savings calculator →
Mirror Edge™: RobbJack's patented polished edge preparation that keeps a flute in contact with the work until the next engages, so the system can't vibrate out of phase — eliminating chatter and unlocking up to 5× the metal removal in aluminum. Chatter control →
Neck & Reach: A necked tool has a reduced-diameter section behind the cutting edge so it can reach into deep pockets while keeping the body short and rigid. Reach is how deep it can get; the neck provides clearance without sacrificing stiffness.
PCD (Polycrystalline Diamond): A solid diamond cutting edge — the longest-lasting option for abrasive, high-plastic-content materials like carbon fiber and composites. It shears fiber cleanly where carbide tears, and it's re-sharpenable. PCD diamond tools →
PVD Coating: A thin, hard film deposited on the tool by physical vapor deposition — AlTiN for heat, TiCN for abrasion, TiN general-purpose, DLC for non-ferrous. The right coating multiplies tool life and finish. Tool coatings →
Rockwell Hardness (HRc): The Rockwell C scale for hardened steels. Pre-hardened mold steels run ~30–45 HRc; fully hardened tool steels reach 50–65 HRc. RobbJack's die/mold carbide cuts up to 65 HRc, dry. Die/Mold & hard metals →
Slotting vs. Profiling: Slotting engages the full tool width (a closed cut) and is the most demanding case; profiling takes a partial radial width along an edge. The two call for different speeds, feeds, and chip-load strategies.
Spindle Speed (RPM): Revolutions per minute of the spindle. Derived from the target surface speed and tool diameter — a small tool needs far more RPM than a large one to hit the same SFM. Machining formulas →
Surface Speed (SFM): Surface feet per minute — how fast the cutting edge travels past the work. It's set by the work material (aluminum runs high, Inconel low) and converts to spindle RPM through the tool diameter: RPM = SFM × 3.82 ÷ diameter. Machining formulas →
TIR (Total Indicator Runout): How far a tool or arbor wobbles off true as it spins, measured with a dial indicator. Excess runout overloads one flute, wrecks finish, and shortens tool life. RobbJack arbors hold TIR to .0002" or better. Slitting saws & arbors →
Tool Deflection: The elastic bending of a tool under cutting load, which makes walls lean and sizes drift. Deflection grows with the cube of unsupported length, so a shorter or necked tool resists it far better than a feed change. Fix dimensional inaccuracy →
Trochoidal Milling: A rolling, curved toolpath that keeps the radial engagement small and constant, so the edge spends less of each revolution buried in the cut. Controlling the arc of engagement controls heat — the key to running titanium and hardened steel faster. Advanced tool paths →
Width of Cut (WOC / Stepover): Radial depth — how much of the tool's diameter is engaged across the cut. Small radial widths (the basis of trochoidal milling) control heat and let you push surface speed in tough alloys.

Put the terms to work

The Speeds & Feeds calculator turns these into tested numbers for your exact tool and material — or browse the Tool Finder.