Why raise the feed when I take a lighter stepover?

Because the chip gets thinner than the feed per tooth once radial engagement drops below half the diameter. At 10% engagement the chip is 60% of the feed per tooth, so catalog feed would rub instead of cut.

Is there a limit to how far chip thinning can raise feed?

The geometry keeps climbing as the stepover shrinks: the factor is 1.67 at 10% engagement and 3.57 at 2%. The machine does not, so watch the share of machine max feed.

Does chip thinning apply to a full slot?

No. From 50% radial engagement up to a full slot, the widest chip equals the feed per tooth. The factor is 1, so program the catalog chip load directly.

Why does the chip load chart change with cutter diameter?

Tool makers rate chip load by cutter size: one published 6061 chart runs from 0.001 in per tooth at 1/8 in to 0.007 in at 1 in. Read the column for your cutter.

CNC Machining calculator

CNC Feed Rate Calculator

Find the feed that gives each tooth the catalog chip load, corrected for chip thinning at light stepovers. You need RPM, flutes, chip load, tool diameter, stepover and the machine's max cutting feed.

What this calculator does

Milling feed rate that holds the catalog chip load at your radial engagement, checked against the machine's feed limit.

Formula used

Radial engagement = radial depth of cut ÷ tool diameter × 100
Chip thinning factor = tool diameter ÷ (2 × √(radial depth × (tool diameter − radial depth))) below 50% engagement, else 1
Chip load to program = catalog chip load × chip thinning factor
Feed rate (in/min) = spindle speed × flutes × chip load to program (uncorrected: catalog chip load)
Share of machine max feed = feed rate ÷ machine max cutting feed × 100

Inputs explained

Spindle Speed: Programmed spindle speed from your surface speed calculation.
Flutes: Cutting flutes on the end mill, or inserts on a face mill.
Catalog Chip Load: Chip load per tooth from the tool maker's chart for this diameter.
Tool Diameter: Cutting diameter of the end mill or face mill.
Radial Depth of Cut: Stepover from CAM; enter the tool diameter for a full slot.
Machine Max Cutting Feed: Maximum cutting feed from the machine's specification sheet.

How to use the result

Best suited to setting adaptive roughing feeds in CAM, finishing a wall at a light stepover, turning a catalog chip load into in/min.
Straight-line cuts only: inside corners and arcs raise engagement, so reduce feed there. Ignores lead angle and ball nose chip thinning, spindle power and tool deflection.

Current U.S. benchmarks

The producer price index for steel mill products stands at 381.162 (BLS, Aug 2026), up 23.4% from a year earlier. Quotes priced off last quarter's material cost miss this move.
The U.S. has 17,154 machine shops establishments employing about 223,303 workers (Census County Business Patterns, 2023).

Common questions

Why raise the feed when I take a lighter stepover? Because the chip gets thinner than the feed per tooth once radial engagement drops below half the diameter. At 10% engagement the chip is 60% of the feed per tooth, so catalog feed would rub instead of cut.
Is there a limit to how far chip thinning can raise feed? The geometry keeps climbing as the stepover shrinks: the factor is 1.67 at 10% engagement and 3.57 at 2%. The machine does not, so watch the share of machine max feed.
Does chip thinning apply to a full slot? No. From 50% radial engagement up to a full slot, the widest chip equals the feed per tooth. The factor is 1, so program the catalog chip load directly.
Why does the chip load chart change with cutter diameter? Tool makers rate chip load by cutter size: one published 6061 chart runs from 0.001 in per tooth at 1/8 in to 0.007 in at 1 in. Read the column for your cutter.

Related guides

Last reviewed 2026-10-01.