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Tool Belt Calc

Measure

Feeds and Speeds Calculator

Feed rate from spindle speed, flutes and chip load.

Your measurementsEvery assumption editable01

From the tooling data for your material and tool diameter.

Feed rateCalculated live02

Result

36.8in/min

36.8 IPM feed rate

Spindle speed
2300 rpm
Flutes
4
Chip load per tooth
0.004 in
Feed per revolution
0.016 in
Feed raterpm × flutes × chip load
36.8 in/min
In metric
934.7 mm/min

Chip load is the input that matters and the one people guess at. Too light and the tool rubs rather than cuts, which generates heat and dulls the edge faster than cutting hard does. Too heavy and it breaks.

Feed and speed are a pair. Changing rpm without changing feed changes the chip load, which is the thing the tool actually experiences — so adjusting one always means recalculating the other.

These are starting figures for a full-width cut. Radial engagement below about half the tool diameter allows chip thinning, where the feed can be increased substantially without raising the actual chip thickness.

Feed rate is spindle speed times flutes times chip load. Chip load is the input that matters and the one people guess at — too light and the tool rubs rather than cuts, which kills an edge faster than cutting hard does.

Why use this tool?What it does differently03

Why use this tool?

The full relationship

Feed per tooth, per revolution and per minute, so you can see where the number comes from.

Rubbing explained

Too little chip load generates heat instead of chips and dulls the tool faster than a heavy cut.

Metric feed

Millimetres per minute alongside, for machines and data in metric.

Chip thinning noted

Light radial engagement allows a substantially higher feed at the same real chip thickness.

How this worksThe method04

How this feeds and speeds calculator works

Feed rate in inches per minute is spindle speed times the number of flutes times the chip load per tooth. Each flute takes one bite per revolution, so the bites multiply.

Chip load is what the cutting edge actually experiences, and it is the figure the tooling data specifies. Feed and speed are therefore a pair: changing rpm without changing feed changes the chip load, which is the thing that matters.

These figures assume a full-width cut. When radial engagement drops below about half the tool diameter, chip thinning means the actual chip is thinner than the programmed feed implies — and the feed can be raised substantially to compensate.

How to use itStep by step05

How to use it

  1. Step 1: Set the spindle speed

    From the SFM to RPM calculator for your material and tool.

  2. Step 2: Enter the flute count

    Two for most aluminium cutters, three or four for steel.

  3. Step 3: Look up the chip load

    From the tooling data for your material and diameter. This is the input worth getting right.

  4. Step 4: Adjust for engagement

    Light radial cuts allow a higher feed thanks to chip thinning.

Example usageWorked figures06

Example usage

A four-flute cutter in steel
2,300 rpm, 4 flutes, 0.004 in chip load gives 36.8 IPM.
A two-flute cutter
The same speed and chip load with 2 flutes halves the feed to 18.4 IPM — flute count scales it directly.
Raising the chip load
The four-flute cutter at 0.006 in rather than 0.004 gives 55.2 IPM. A heavier chip is often kinder to the tool than a light one.
Frequently asked questionsCommon questions07

Frequently asked questions

How do I calculate feed rate?

Spindle speed times the number of flutes times the chip load per tooth. That gives inches per minute directly.

What is chip load?

The thickness of material each cutting edge removes per revolution. It is the figure tooling data specifies and the one that determines tool life.

Why is too slow a feed bad?

Because the edge rubs rather than cuts. Rubbing generates heat without forming a chip to carry it away, and it dulls a tool faster than a properly loaded cut does.

What is chip thinning?

When radial engagement is less than half the tool diameter, the actual chip is thinner than the programmed feed suggests. The feed can be increased to bring real chip thickness back to target.

Do I change feed when I change speed?

Yes. Chip load is feed divided by speed and flutes, so changing one without the other changes what the tool actually experiences.

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