Guide
Chip Load Guide
Use feed per tooth to decide whether each cutting edge is cutting cleanly, rubbing, or overloaded before you raise feed rate.
Solve the Numeric Feed Rate
Use the calculator when RPM, flute count, and target chip load are known and you need feed rate in IPM.
Direct answer: chip load is feed rate divided by RPM and flute count; use it to decide whether the edge is cutting, rubbing, or overloaded.
Use this guide for chip-load method and chip-thinning support; the live calculator handles numeric feed-rate solving.
What is Chip Load?
Chip Load (also known as Feed Per Tooth or IPT) is the size of the material slice that each cutting edge of the tool removes during one revolution.
It is physically the thickness of the chip.
What this guide covers best
Start here when your question starts with feed per tooth, IPT, or chip thinning. If you still need spindle speed first, start with the RPM calculator or the SFM to RPM guide, then come back here to turn RPM into feed rate and chip thickness targets. For a full cutter setup that keeps RPM, feed rate, chip load, SFM, MRR, and power together, use the CNC feeds and speeds calculator.
- Why it matters:
- Too Small: Variations in material/cutter mean the edge rubs instead of cuts. Friction = Heat = Work Hardening.
- Too Large: Cutting forces exceed the strength of the tool or the flute space, increasing breakage and flute-packing risk.
The Formula
To find Feed Rate (IPM):
IPM = RPM × IPT × Flutes
Standard Chip Load Starting Points (1/2" End Mill)
Values are for a standard 1/2" Carbide End Mill. Scale down for smaller tools (e.g., 1/4" tool = 50% of these values).
| Material | Roughing IPT | Finishing IPT |
|---|---|---|
| Aluminum (6061) | 0.003" - 0.008" | 0.001" - 0.003" |
| Low Carbon Steel (1018) | 0.002" - 0.004" | 0.001" - 0.002" |
| Stainless (304) | 0.0015" - 0.003" | 0.0008" - 0.0015" |
| Titanium (6Al-4V) | 0.001" - 0.0025" | 0.0005" - 0.0015" |
| Plastics (Delrin/ABS) | 0.006" - 0.012" | 0.003" - 0.005" |
Don't Forget Chip Thinning!
If your radial width of cut (stepover) is less than 50% of the cutter diameter, your actual chip load is thinner than calculated.
The Fix: You must increase your feed rate to maintain the target chip thickness.
A common radial chip thinning factor is RCTF = 1 / √(1 - (1 - (2 × WOC / Dia))²). At 10% radial engagement, that works out to about 1.67× feed increase.
Read the full explanation in our Feeds & Speeds Guide →Quick Rule of Thumb: Scaling by Diameter
A good starting point for chip load is often based purely on cutter diameter:
Standard Rule (End Mills)
Start with 0.2% - 0.8%
of cutter diameter for many end-mill jobs
Example: 1/2" tool × 0.004 = 0.002" IPT. Harder materials are often below this shortcut.
Face Mills
0.005" - 0.020"
Fixed Range
Large inserts can handle heavy loads.
Related Guides
Face-mill setups use a different chip-load release path: start with the face-mill speeds and feeds table, then return to chip load only after cutter diameter, insert count, and SFM are realistic.
Frequently Asked Questions
What is chip load (IPT) in CNC machining?
Chip load (IPT — Inches Per Tooth) is the thickness of material each cutting edge removes per revolution. Formula: IPT = Feed Rate (IPM) / (RPM × Number of Flutes). It is the single most important parameter for tool life.
What is the recommended chip load for aluminum?
For a 1/2-inch carbide end mill in 6061 aluminum: roughing chip load is 0.003–0.008 inches, finishing chip load is 0.001–0.003 inches. Scale proportionally for other diameters.
How do I calculate feed rate from chip load?
Feed Rate (IPM) = RPM × Chip Load (IPT) × Number of Flutes. Example: 6,000 RPM × 0.004" IPT × 3 flutes = 72 IPM.
What happens if chip load is too low?
When chip load is too small, the tool rubs instead of cutting. This generates excessive friction heat, causes work hardening (especially in stainless steel), and leads to premature tool wear and built-up edge (BUE).
What is the chip load rule of thumb for end mills?
A rough end-mill shortcut is to start somewhere around 0.2% to 0.8% of cutter diameter, then narrow the value with material, flute count, and engagement. For example, a 1/2-inch tool at 0.4% gives about 0.002 inch IPT. Free-cutting aluminum may support more, while stainless and titanium are often below that shortcut. Face mills are usually validated from insert-maker tables and cutter geometry rather than a single universal diameter rule.