# Kerfwise CNC Feeds & Speeds Calculator

> CNC router rpm, feed, chip load with chip thinning, removal rate and spindle power. Calculates a starting spindle speed and feed rate for a CNC router or mill: rpm from cutting speed and diameter (or your spindle speed), feed = rpm × flutes × chip load, chip loads from a published router-bit chart for wood, plywood, MDF, plastics, acrylic and aluminium, the depth-of-cut reduction, radial chip thinning for light side cuts, material removal rate and a power estimate from the specific cutting energy. Metric or imperial.

Part of usefulweb.app (https://usefulweb.app/). Part of [Kerfwise](https://kerfwise.usefulweb.app/) (ownerApp: kerfwise). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://kerfwisefeedsspeeds.usefulweb.app/ (interactive tool at https://kerfwisefeedsspeeds.usefulweb.app/tool)
- JSON API: POST https://kerfwisefeedsspeeds.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://kerfwisefeedsspeeds.usefulweb.app/api/v1/tool)
- OpenAPI: https://kerfwisefeedsspeeds.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://kerfwisefeedsspeeds.usefulweb.app/mcp - tool `kerfwise_feeds_speeds`

## Inputs
- units (select): Units
- material (select): Material
- diameter (number): Cutter diameter - mm (metric) or inch (imperial).
- flutes (integer): Flutes (cutting edges)
- rpm (integer): Spindle speed - Used when no cutting speed is entered.
- cuttingSpeed (number): Cutting speed (optional) - m/min (metric) or SFM (imperial). When set, the spindle speed is calculated from it.
- spindleMinRpm (integer): Spindle minimum (optional)
- spindleMaxRpm (integer): Spindle maximum (optional)
- chipLoad (number): Chip load per tooth (optional) - mm or inch. Required for a custom material; overrides the chart otherwise.
- chipLoadPosition (select): Start in the chart range at
- radialEngagement (number): Radial engagement ae (optional) - Width of cut, mm or inch. Empty = full slot (ae = diameter). Below half the diameter the feed is raised for chip thinning.
- axialDepth (number): Depth of cut ap (optional) - mm or inch. Empty = one diameter.
- specificEnergy (number): Specific cutting energy (optional) - W·s/mm³ (1 hp·min/in³ = 2.73 J/mm³). Empty = the material’s planning value, where one is built in.
- efficiency (number): Spindle efficiency

## Method
- Spindle speed n = Vc × 1000 / (π × D) with Vc in m/min and D in mm (imperial: n = SFM × 12 / (π × D) with D in inch), limited to the spindle minimum and maximum. Without a cutting speed your spindle speed is used and the resulting cutting speed is shown.
- Chip load per tooth: the published router-bit chart gives a low–high range at 1/8, 1/4, 3/8 and 1/2 inch (and larger); between the columns the range is interpolated linearly, below 1/8 inch it is scaled with the diameter. You choose the low end, the middle or the high end, or enter your own chip load.
- Depth of cut: up to 1 × D the chart value is used, at 2 × D it is reduced by 25 % and at 3 × D by 50 % (linear in between).
- Radial chip thinning: with a side cut narrower than half the diameter the real chip is thinner than the feed per tooth, so the programmed chip load is raised by 1 / √(1 − (1 − 2 ae/D)²) to keep the target chip thickness.
- Feed vf = n × flutes × programmed chip load. Material removal rate Q = ae × ap × vf. Cutting power P = Q × specific cutting energy; spindle power = P / efficiency.

## Limits
- Chart values are starting points for rigid machines and sharp solid-carbide bits. Start at the low end, listen and look at the chips, then adjust. Check the tool maker’s data and your machine’s limits.