Chip load calculator

Chip load is the thickness of material each cutting edge removes during one spindle revolution, measured in inches per tooth. It ties your three machine settings together: feed rate equals RPM times the number of flutes times the chip load. Because the chip itself carries heat away from the cut, chip load is the single best knob for balancing surface finish against tool life.

Multiply spindle speed by the number of flutes and the target chip load: Feed rate (IPM) = RPM × flutes × chip load. For example, a 2-flute tool at 18,000 RPM with a 0.010" chip load should feed at 360 inches per minute.

Chips that are too thin can't carry heat out of the cut, so the tool rubs and burnishes instead of cutting. That heat burns the material, work-hardens some plastics and metals, and dulls the cutting edges much faster. If you see burning or dust instead of chips, feed faster or slow the spindle.

The tool deflects under the heavier cutting load, which causes chatter, edge blowout, a poor finish, and in the worst case a broken tool. If the machine sounds labored or the edge quality drops, reduce the feed rate or add spindle speed to thin the chip.

The deeper the tool is buried, the more it deflects, so reduce chip load as depth increases. Up to one tool diameter deep, run the recommended chip load. At two times the diameter, reduce it by 25%. At three times, reduce it by 50%.

It depends on the tool diameter: bigger tools take bigger bites. As broad baselines, hardwood runs 0.005"-0.020", softwood 0.002"-0.020", hard plastics 0.004"-0.012", and aluminum 0.001"-0.004". Use the chart on this page for ranges by diameter, start in the middle, and adjust from what the cut tells you.

Surface speed is how fast the cutting edge itself travels through the material, measured in surface feet per minute: SFM = (π × diameter × RPM) ÷ 12. Chip load sets the bite per tooth; surface speed sets the edge speed and the heat at the edge. In metal cutting you typically pick RPM from the material's rated SFM first, then set the feed from chip load. In wood routing, chip load usually leads and SFM is a sanity check.

RPM = (SFM × 12) ÷ (π × diameter), or roughly SFM × 3.82 ÷ diameter. For example, a 1/2" tool targeting 2,000 SFM runs at about 15,280 RPM. Larger tools reach the same surface speed at lower RPM, which is why big cutters spin slower.

Yes, the relationships are identical, only the units change. Chip load in millimeters per tooth is inches × 25.4, and feed rate in meters per minute is IPM × 0.0254. The calculator shows metric conversions alongside every result.

A few common ones: when cutting grooves or dados with a downcut spiral, reduce the calculated feed rate about 30% because the chips get re-cut in the slot. Plastics generally like lower spindle speeds (around 14,000 RPM) to avoid melting. And for a specific tool number, the manufacturer's cutting data beats any generic chart, so send it to us and we'll look it up.