What is the difference between feed rate and chip load?

Chip load is feed per cutting tooth. Table feed is chip load multiplied by the number of teeth and spindle RPM.

Why does cutter diameter change RPM?

At the same cutting speed, a larger circumference covers more distance per revolution, so a larger cutter needs lower RPM.

Can I use generic values for production?

Use them as a conservative planning or prove-out starting point. Production values should be based on exact tool guidance and proven machine, holder, material and engagement conditions.

CNC Speeds and Feeds — RPM, Feed Rate & Chip Load Explained

The two inputs behind RPM and feed

Cutting speed vc describes the surface speed at the cutter circumference. Chip load fz is the intended feed per tooth. Once those values are selected, spindle speed follows from cutter diameter and table feed follows from spindle speed and flute count.

For metric units: n = (vc × 1000) / (π × D), and vf = fz × z × n. A formula-only calculator starts after the difficult decision. A useful starter guide first narrows vc and fz from the material and tool context, then keeps those planning values visible in the result.

Material name is not enough

Two materials with similar names can machine differently because of hardness, heat treatment, strength, work hardening and condition. When hardness is known, include it. When it is not known, use the cautious end of a broad planning range and identify the uncertainty.

The exact tool manufacturer's data should take priority because substrate, coating, edge preparation, flute geometry and intended application are tool-specific.

Engagement changes the starting point

A full-width slot, deep pocket and light radial finishing pass do not load the cutter in the same way. Radial engagement, axial depth and tool stick-out influence force, heat, chip evacuation and stability. Use the same material label with different planning values when the operation changes substantially.

Material-removal rate Q = ap × ae × vf / 1000 in cm³/min makes the combined effect of depth, width and feed visible, but it does not prove the spindle has enough power or that the setup is stable.

A safe shop-floor sequence

Start from the exact tool documentation where available. Check the requested RPM against spindle limits and the feed against controller and machine limits. Confirm holder, stick-out, coolant, workholding and chip evacuation. Prove the cut conservatively, then adjust using sound, chip formation, spindle load, finish, wear and measured results.

Do not exceed cutter or holder speed limits.
Reduce the starting point for uncertain rigidity or long reach.
Do not correct poor chip evacuation only by reducing feed until rubbing occurs.
Record proven shop values with their machine, tool, material and engagement context.

Why Dimvo labels planning data

A generic recommendation is useful for planning only when its limits are visible. Dimvo separates generic planning profiles from manufacturer data and future shop-proven values. The calculator shows the selected values before it shows RPM and feed, so the engineer can replace them when better evidence is available.

CNC speeds and feeds explained