Calculate feed per tooth (IPT / fz) for carbide end mills. Optimize chip load to maximize tool life, surface finish, and material removal rate.
Based on recommended chip load ranges from carbide tooling manufacturers and the Machining Data Handbook
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Chip load, also known as feed per tooth (fz in metric or IPT — Inches Per Tooth — in imperial), is the thickness of material removed by each cutting edge of the tool per revolution. It is the single most important parameter affecting tool life, surface finish, and machining productivity. An optimized chip load ensures that the cutting edge is actually cutting, not rubbing — rubbing causes heat buildup, work-hardening, and premature tool failure.
Imperial: IPT = Feed Rate (IPM) ÷ (RPM × Number of Flutes)
Metric: fz (mm/tooth) = Vf (mm/min) ÷ (n × z)
Where Vf = feed rate, n = spindle speed (RPM), z = number of flutes.
Inversely, to calculate the required feed rate for a target chip load:
Feed Rate = Target IPT × RPM × Number of Flutes
Aluminum 6061: 0.003-0.006 IPT roughing, 0.001-0.003 IPT finishing. Aluminum permits aggressive chip loads due to its low cutting forces. Use 2-3 flute tools for maximum chip evacuation.
Stainless Steel 304/316: 0.002-0.005 IPT roughing, 0.001-0.003 IPT finishing. Stainless steel work-hardens if the chip load is too low — maintaining minimum chip thickness is critical. Never drop below 0.001 IPT with carbide tools in stainless.
Titanium Grade 5: 0.001-0.003 IPT roughing, 0.0008-0.002 IPT finishing. Titanium's low thermal conductivity means the chip carries away most of the heat. Adequate chip load ensures heat doesn't concentrate at the cutting edge.
Hardened Steel (45-55 HRC): 0.001-0.003 IPT roughing, 0.0005-0.002 IPT finishing. Use light chip loads with high-flute-count tools. Trochoidal toolpaths allow higher chip loads at reduced radial engagement.
Running below the minimum recommended chip load causes the tool to rub rather than shear. This rubbing generates excessive heat, leads to work-hardening in stainless steels and nickel alloys, and accelerates flank wear. Running above the maximum chip load risks tool deflection, edge chipping, and spindle overload. The optimal chip load balances material removal rate with predictable tool life — typically targeting the middle to upper end of the recommended range for roughing operations.
Too low: Burnt edges, discolored chips, squealing or whistling sounds, poor surface finish, rapid flank wear.
Too high: Tool deflection, chatter marks, broken cutting edges, spindle load exceeding 100%, oversized hole or slot dimensions.
What is chip load in CNC milling? Chip load (IPT or fz) is the thickness of material removed by each cutting flute per revolution. It determines whether the tool cuts efficiently or rubs against the material.
How do I calculate feed per tooth? Divide the feed rate by the product of spindle speed and number of flutes: fz = Vf ÷ (n × z). Use the calculator above for instant results.
What happens if chip load is too low? The tool rubs instead of cutting, generating excessive heat, causing work-hardening, and dramatically reducing tool life. In stainless steel, low chip load is the #1 cause of premature failure.
What is the difference between IPT and fz? IPT (Inches Per Tooth) and fz (feed per tooth in mm) are the same concept — just different units. IPT × 25.4 = fz in mm/tooth.
How does chip load affect surface finish? Lower chip loads generally produce finer surface finishes, but only if the tool is cutting (not rubbing). The theoretical finish is a function of feed per tooth and corner radius: Rt = (fz²) ÷ (8 × R).
Should chip load change for high-speed machining? For HSM/trochoidal toolpaths, you can increase chip load by 30-50% compared to conventional paths because the reduced radial engagement allows each tooth to take a thicker chip.