CNC / machinist calculator
Chip Load Calculator
Chip load is one of the key numbers behind whether an end mill cuts cleanly or burns up, alongside surface speed and depth of cut. This calculator works both ways: enter your RPM, flute count and a target chip load to get the table feed rate, or enter the feed rate you are running to discover the chip load each flute is actually taking. It is the fast way to check that a feed you copied from somewhere is not quietly rubbing the edge or overloading a flute.
How it works
Every flute on a rotating cutter takes one bite per revolution, so the thickness of that bite, the chip load, ties feed rate to spindle speed. Feed rate in inches per minute equals RPM times the number of flutes times the chip load. Rearranged, the chip load is the feed rate divided by RPM times flutes.
Running too light is the most common and most damaging mistake. Below a material-dependent minimum the edge stops cutting and starts rubbing, which generates heat instead of chips, work-hardens stainless and titanium, and dulls the tool fast. Running too heavy is the opposite failure: the chip is thicker than the flute can clear and the tool deflects, chatters or breaks.
Match the chip load to the tool diameter and material. Small tools take tiny chips measured in ten-thousandths of an inch; larger tools in tougher metals take more. The feeds and speeds calculator suggests a starting chip load by diameter for each material in the cutting-data table.
Worked example
A two-flute cutter at 3000 RPM and a 0.002 in chip load: feed = 3000 x 2 x 0.002 = 12.0 in/min. Double the flutes to four and the feed doubles to keep the same chip per tooth. A two-flute cutter at 3000 RPM and a 0.05 mm chip load: feed = 3000 x 2 x 0.05 = 300 mm/min. Double the flutes to four and the feed doubles to keep the same chip per tooth.
Starting chip load chart (in/toothmm/tooth)
Starting feed per tooth by material and end-mill diameter, for solid carbide. Smaller tools take a lighter chip; scale between the columns for in-between sizes. Each material's values and sources are on the cutting-data page.
| Material | 1/8" 3 mm | 1/4" 6 mm | 1/2" 12 mm |
|---|---|---|---|
| Aluminum 2024 | 0.0010 0.025 | 0.0020 0.051 | 0.0040 0.102 |
| Aluminum 6061 | 0.0010 0.025 | 0.0020 0.051 | 0.0040 0.102 |
| Aluminum 7075 | 0.0010 0.025 | 0.0019 0.048 | 0.0038 0.097 |
| Alloy Steel 4140 | 0.0006 0.015 | 0.0013 0.033 | 0.0026 0.066 |
| Alloy Steel 4340 | 0.0006 0.015 | 0.0013 0.033 | 0.0026 0.066 |
| C45W Carbon Steel (1.1730) | 0.0006 0.015 | 0.0013 0.033 | 0.0026 0.066 |
| Mild Steel 1018 | 0.0007 0.018 | 0.0015 0.038 | 0.0030 0.076 |
| Steel 12L14 (free-machining) | 0.0008 0.020 | 0.0016 0.041 | 0.0032 0.081 |
| 1.2767 Tool Steel (45NiCrMo16) | 0.0006 0.015 | 0.0012 0.030 | 0.0024 0.061 |
| D2 Tool Steel | 0.0003 0.008 | 0.0006 0.015 | 0.0012 0.030 |
| O2 Tool Steel | 0.0004 0.010 | 0.0008 0.020 | 0.0016 0.041 |
| Stainless Steel 303 (free-machining) | 0.0006 0.015 | 0.0013 0.033 | 0.0026 0.066 |
| Stainless Steel 304 | 0.0006 0.015 | 0.0012 0.030 | 0.0025 0.064 |
| Titanium Ti-6Al-4V | 0.0005 0.013 | 0.0010 0.025 | 0.0020 0.051 |
| Gray Cast Iron | 0.0008 0.020 | 0.0016 0.041 | 0.0032 0.081 |
| Brass 360 (free-cutting) | 0.0010 0.025 | 0.0020 0.051 | 0.0040 0.102 |
| Copper C110 (ETP) | 0.0010 0.025 | 0.0020 0.051 | 0.0040 0.102 |
| Acetal (Delrin) | 0.0010 0.025 | 0.0025 0.064 | 0.0050 0.127 |
| Hardwood (oak, maple, walnut) | 0.0040 0.102 | 0.0100 0.254 | 0.0200 0.508 |
| MDF / Particleboard | 0.0055 0.140 | 0.0145 0.368 | 0.0260 0.660 |
| Softwood / Plywood (pine, fir, birch ply) | 0.0050 0.127 | 0.0120 0.305 | 0.0220 0.559 |
Below about half the tool diameter of radial engagement, raise the programmed chip load for radial chip thinning - the feeds and speeds calculator does this automatically.
Frequently asked questions
What is chip load in milling?
Chip load, also called feed per tooth, is the thickness of material each flute removes in one revolution. It links spindle RPM and feed rate and is the key to a cut that produces chips rather than heat.
How do I calculate feed rate from chip load?
Multiply the spindle RPM by the number of flutes by the chip load in inches per tooth. A 3000 RPM two-flute cutter at 0.002 inch chip load runs a 12 inch-per-minute feed.
What happens if the chip load is too low?
The edge rubs instead of cutting, which makes heat instead of chips. That work-hardens stainless and titanium, glazes the cutting edge and shortens tool life dramatically, often faster than running too heavy.
Does chip load depend on tool diameter?
Yes. Small-diameter tools are fragile and take chips measured in ten-thousandths of an inch, while larger tools take proportionally more. Published charts list chip load by diameter for each material.
Is chip load the same as feed rate?
No. Chip load is per tooth per revolution, while feed rate is the linear table speed in inches per minute. Feed rate is chip load scaled up by the RPM and the number of flutes.
Related calculators
Sources
Every formula on this page is shown and sourced. See how we verify.
These calculators are for planning and as a starting point. Recommended speeds and feeds are published starting values that vary with your specific tool, coating, machine rigidity, workholding and coolant. Always start conservative, listen to the cut, and follow your tool maker data sheet.