What is chip load in CNC machining?

Chip load, or feed per tooth, is how much material each cutting edge removes per revolution, in inches per tooth. It equals Feed Rate divided by (Spindle Speed x Number of Flutes). It matters because too little causes rubbing and heat while too much fractures the edge. For 80 IPM at 7,500 RPM on a 4-flute tool, chip load is 0.00267 in/tooth. Compare it to the tool maker's range for your material.

How do I calculate chip load from feed rate and RPM?

Divide feed rate by the product of spindle speed and flute count: Chip Load = Feed Rate / (Spindle Speed x Number of Flutes). Example: 80 IPM / (7,500 RPM x 4 flutes) = 80 / 30,000 = 0.00267 in/tooth. To go the other way and find feed rate, rearrange to Feed Rate = Chip Load x Spindle Speed x Number of Flutes, which is how you program the machine from a catalog value.

What is a good chip load for a 1/4 inch endmill?

It depends on material. A 0.25 inch carbide endmill in aluminum typically wants 0.002 to 0.004 in/tooth; in mild steel, 0.0015 to 0.0025; in stainless, 0.001 to 0.002. Larger tools take bigger bites. Always pull the exact range from the tool maker's chart, since coating and flute geometry shift these numbers. The formula gives your actual chip load, but only the manufacturer's range tells you if it is right.

My tool keeps burning up. Is my chip load too low?

Often yes. When chip load falls below the recommended minimum, the edge rubs rather than cuts, and friction heat instead of the chip carries the energy, so the tool overheats and dulls fast. Check your actual value: if you get 0.001 in/tooth but the catalog wants 0.003, raise feed rate or lower RPM. Discolored, dusty chips confirm rubbing. Thicker chips carry heat away and keep the edge cooler.

How do I convert chip load to millimeters per tooth?

Multiply inches per tooth by 25.4. A chip load of 0.00267 in/tooth equals 0.068 mm/tooth. If you work in metric natively, the formula stays Feed Rate (mm/min) / (Spindle Speed x Number of Flutes), giving mm/tooth directly. Just keep feed rate and chip load in the same unit system; mixing IPM feed with a mm/tooth catalog value will give a wrong feed rate.

What is the difference between chip load and feed rate?

Feed rate is the total table travel in inches per minute, while chip load is what a single tooth removes per revolution, in inches per tooth. Feed rate bundles together RPM, flute count, and chip load. You pick a chip load from the catalog, then multiply by spindle speed and flute count to get the feed rate you actually program. Chip load is the tool-protecting target; feed rate is the machine command.

Engineering and Process

Chip Load Formula

Chip load is the amount of material each cutting edge removes per revolution. Use it to verify whether your programmed feed rate is within the tool's recommended range for the material being cut.

Formula

Chip Load = Feed Rate / (Spindle Speed x Number of Flutes)

Variables

Feed Rate: Programmed or actual feed rate in inches per minute
Spindle Speed: Spindle RPM
Number of Flutes: Number of cutting edges on the tool

Understanding the Chip Load Formula

Chip load is the thickness of material each cutting edge peels off per revolution, and it is the truest indicator of whether a tool is being fed correctly. Too little and the edge rubs instead of cutting, generating heat that dulls the tool; too much and you overload the edge and risk fracture. The whole point is to keep each tooth taking a proper bite, which protects tool life and produces clean chips that carry heat away from the cut.

Feed rate is in inches per minute, spindle speed in RPM, and number of flutes is the physical count of cutting edges. The result is inches per tooth (also called feed per tooth). For the worked case, 80 IPM at 7,500 RPM on a 4-flute tool gives 80 / (7,500 x 4) = 0.00267 in/tooth. Note this is the actual chip load; catalogs usually list it as a target, so you often rearrange the formula to solve for feed rate instead.

The number is meaningless until compared to the tool maker's recommended range for that material. A 0.5 inch carbide endmill in aluminum might want 0.004 to 0.008 in/tooth, so 0.00267 is too light and the edge will rub. In steel the range may be 0.002 to 0.004, making 0.00267 acceptable. If you are below range, raise feed or lower RPM; if above, do the reverse. Thin, discolored chips signal too low; thick or packed chips signal too high.

Worked Example

Feed rate is 80 IPM. Spindle speed is 7,500 RPM. The tool has 4 flutes.

Chip load = 80 / (7,500 x 4)
= 80 / 30,000
= 0.00267 inches per tooth

Result: 0.00267 in/tooth - compare against manufacturer's recommended range

Common Mistake

Accepting the result without comparing to the tool manufacturer's range. The formula gives you the actual chip load. It is only useful when compared against the manufacturer's minimum and maximum recommended chip loads for that tool and material combination.

Frequently Asked Questions

What is chip load in CNC machining?: Chip load, or feed per tooth, is how much material each cutting edge removes per revolution, in inches per tooth. It equals Feed Rate divided by (Spindle Speed x Number of Flutes). It matters because too little causes rubbing and heat while too much fractures the edge. For 80 IPM at 7,500 RPM on a 4-flute tool, chip load is 0.00267 in/tooth. Compare it to the tool maker's range for your material.
How do I calculate chip load from feed rate and RPM?: Divide feed rate by the product of spindle speed and flute count: Chip Load = Feed Rate / (Spindle Speed x Number of Flutes). Example: 80 IPM / (7,500 RPM x 4 flutes) = 80 / 30,000 = 0.00267 in/tooth. To go the other way and find feed rate, rearrange to Feed Rate = Chip Load x Spindle Speed x Number of Flutes, which is how you program the machine from a catalog value.
What is a good chip load for a 1/4 inch endmill?: It depends on material. A 0.25 inch carbide endmill in aluminum typically wants 0.002 to 0.004 in/tooth; in mild steel, 0.0015 to 0.0025; in stainless, 0.001 to 0.002. Larger tools take bigger bites. Always pull the exact range from the tool maker's chart, since coating and flute geometry shift these numbers. The formula gives your actual chip load, but only the manufacturer's range tells you if it is right.
My tool keeps burning up. Is my chip load too low?: Often yes. When chip load falls below the recommended minimum, the edge rubs rather than cuts, and friction heat instead of the chip carries the energy, so the tool overheats and dulls fast. Check your actual value: if you get 0.001 in/tooth but the catalog wants 0.003, raise feed rate or lower RPM. Discolored, dusty chips confirm rubbing. Thicker chips carry heat away and keep the edge cooler.
How do I convert chip load to millimeters per tooth?: Multiply inches per tooth by 25.4. A chip load of 0.00267 in/tooth equals 0.068 mm/tooth. If you work in metric natively, the formula stays Feed Rate (mm/min) / (Spindle Speed x Number of Flutes), giving mm/tooth directly. Just keep feed rate and chip load in the same unit system; mixing IPM feed with a mm/tooth catalog value will give a wrong feed rate.
What is the difference between chip load and feed rate?: Feed rate is the total table travel in inches per minute, while chip load is what a single tooth removes per revolution, in inches per tooth. Feed rate bundles together RPM, flute count, and chip load. You pick a chip load from the catalog, then multiply by spindle speed and flute count to get the feed rate you actually program. Chip load is the tool-protecting target; feed rate is the machine command.