What is chip load and why does it matter?

Chip load is the thickness of material each cutting edge removes per revolution, in inches per tooth. Too small and the edge rubs instead of cutting, generating heat and dulling the tool; too large and the cutter chatters or breaks. It is the single most important feed parameter.

How is chip load calculated from feed rate?

Chip load equals feed rate divided by the product of spindle RPM and the number of flutes. So for 30 IPM at 5000 RPM on a 4-flute cutter, the chip load is 30 / (5000 × 4) = 0.0015 inch per tooth.

My chip load is flagged as too light. What does that mean?

A chip load below the recommended window usually means the cutter is rubbing rather than slicing. Rubbing work-hardens many alloys, builds heat, and accelerates edge wear. Raise the feed rate or lower the RPM to thicken the chip.

What chip load should I use for aluminium?

Typical chip loads for aluminium with a 1/4 inch end mill run roughly 0.002 to 0.005 inch per tooth, higher than steel because aluminium cuts freely. Always cross-check the cutter manufacturer's data for the exact tool and diameter.

Does this account for radial chip thinning?

No. This tool reports the programmed chip load. At radial engagements below half the cutter diameter the actual chip is thinner than programmed, so you can and should increase feed. Use a chip-thinning calculator for light radial cuts.

Chip Load Calculator

Chip load — the feed per tooth — is the parameter that decides whether your end mill slices cleanly, rubs and burns, or chatters and snaps. This tool back-calculates the real chip load from the feed rate you actually ran and compares it to a sensible window for the material, so you can tell rubbing from chatter at a glance.

How it works

Chip load per tooth is the feed rate divided by how many cutting edges pass through the work each minute:

chip load (in/tooth) = feed rate (IPM) / (RPM × number of flutes)

Rearranged, feed rate = chip load × RPM × flutes. So if you know any three of the four values you can solve for the missing one. This calculator solves for chip load, the value you cannot read directly off the machine.

Diagnosing rubbing vs chatter

Each material has a working window. A result below the window means the chip is too thin: the edge plows and rubs, generating heat that work-hardens steels and stainless and glazes the cutting edge. A result above the window means the chip is too thick: cutting forces spike, the tool deflects, and you get chatter or breakage. The fix for rubbing is more feed or less RPM; the fix for chatter is less feed, fewer flutes engaged, or a more rigid setup.

Example and tips

Running 30 IPM at 5000 RPM on a 4-flute cutter gives 30 / (5000 × 4) = 0.0015 inch per tooth. For mild steel that sits near the light end of the window, so a modest feed increase to 40 IPM (0.002 in/tooth) usually cuts cleaner and cooler. These windows are diameter-dependent — larger cutters tolerate larger chips — so treat the flags as a sanity check, not a substitute for the tool maker’s data.