CNC Speeds & Feeds Planner
Turn a tool maker’s chip-load target into a feed rate, inspect radial chip thinning and compare with machine limits.
Quick answer. CNC feed rate equals spindle RPM × cutting flutes × feed per tooth. For an illustrative 18,000 RPM, two-flute cutter and 0.10 mm/tooth, the base feed is 3,600 mm/min. Obtain the chip-load target from the exact cutter and material documentation. See the method and references
Set up your calculation
An illustrative example is loaded. Replace its values with your measurements, costs or documented settings.
Tooling help: Tool geometry · Setup limits
Calculation
Your result
- Calculated feed
- 3,600 mm/min
- Imperial feed
- 141.732 in/min
- Applied thinning factor
- 1 ×
- Surface speed
- 359.084 m/min
- Material removal rate
- 34.29 cm³/min
The quote handoff carries your inputs and assumptions. Only an explicit base cost is suggested as a quote cost; prices, rates and measurements remain planning notes.
How it works
Base feed = RPM × flutes × chip load. For a cylindrical end mill below 50% radial engagement, thinning factor = 1 ÷ √(4r(1−r)), r = width/diameter; otherwise factor = 1. MRR = width × depth × feed.
- Enter documented chip load, depth and RPM for the exact cutter and material. Example values are a math demonstration. The optional thinning correction applies only to steady side milling with a cylindrical end mill.
- Do not apply this correction to V-bits, ball noses, plunging, interrupted cuts or a tool maker’s feed that already includes it. Machine speed limits do not certify cutting safety; workholding, stickout and chip evacuation still matter.
Connect chip load to the feed you program
Formula and units
- Base feed (mm/min) = RPM × flutes × chip load (mm/tooth)
- Chip load = feed ÷ (RPM × flutes)
- Removal rate (cm³/min) = width × depth × feed ÷ 1,000
Width and depth are millimeters. Sandvik’s milling reference defines these feed and removal-rate relationships [1]. The optional correction in this planner uses 1/√(4r(1−r)) below 50% radial engagement, where r = width ÷ cutter diameter; otherwise the factor is 1.
| Spindle RPM | Base feed | Imperial feed |
|---|---|---|
| 12,000 | 2,400 mm/min | 94.5 in/min |
| 18,000 | 3,600 mm/min | 141.7 in/min |
| 24,000 | 4,800 mm/min | 189.0 in/min |
The RPM values are comparison inputs, not recommended wood-cutting settings. There is no universal chip-load range for all router bits. Cutter diameter, geometry, material, engagement and the actual spindle range determine the usable setup.
Check a pocketing estimate before CAM
With the loaded 6.35 mm cutter, 18,000 RPM, two flutes and 0.10 mm/tooth, leave thinning off to get 3,600 mm/min (141.7 in/min). At 3.175 mm width and 3 mm depth, removal rate is 34.29 cm³/min. These inputs demonstrate the math. Confirm them against the cutter documentation before making a cut.
What your result means
- Above the feed limit
- The planner warns rather than reducing the result silently. Re-select RPM and engagement with tool guidance. Reducing feed alone also changes feed per tooth.
- Below 50% radial engagement
- Thinning correction is an optional idealized steady side-cut model. Leave it off when the manufacturer’s recommendation already includes compensation or when the toolpath does not match the model.
Assumptions and limits
The calculation does not simulate acceleration, tool deflection, holding force or available spindle power. Thinning correction does not apply to V-bits, ball noses, plunges or interrupted cuts. A feed below the entered machine limit is not proof that a cut is suitable.
Sources and content notes
- Sandvik Coromant: milling formulas and definitions
Feed per tooth, spindle speed, table feed, engagement and material-removal definitions. This reference does not supply woodworking chip loads for your cutter.
Maintained by WoodWorkCalc · Reference content updated . Equations and worked values were checked against the calculator implementation. Scenarios are illustrative; they are not field-test records or independent technical certification.
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