CNC Feeds & Speeds Calculator
Enter your cutter size, flute count, and the material you are cutting to get safe starting RPM, feed rate, and depth of cut - with a quick deflection risk check. Everything runs in your browser, nothing uploaded.
Cutter Diameter
Flute Count
Material
Cutting Type
Machine Max RPM
Recommended Settings
RPM Usage
Learn more: CNC feeds, speeds, and chip load explained
Chip load: the core number in CNC routing
Chip load is how much material each cutting edge removes per tooth per revolution, measured in mm or inches. Too little causes rubbing and burning; too much causes deflection and broken bits. The ideal chip load depends heavily on material: wood tolerates roughly 0.1-0.2mm per tooth, while aluminium needs much less at 0.025-0.075mm. The cutting type matters too - slotting (full-width) tolerates 80% of standard chip load, profiling (edge cut) tolerates 120%.
SFM and RPM: why tooling catalogues are not enough
Tooling manufacturers publish SFM (surface feet per minute) ranges, not ready-to-use RPM numbers. You must convert for your specific cutter diameter, account for your machine's max RPM, and adjust for your material. Mistakes cost bits that run 15-80 USD each. This calculator does the full SFM-to-RPM conversion, adjusts chip load for cutting type, and shows your RPM relative to machine limits via the gauge.
Deflection risk and chatter
Deflection (tool bending under cutting forces) causes chatter, poor surface finish, and broken bits. Long, thin tools in high-speed, high-load conditions deflect easily. The calculator flags deflection risk based on cutter diameter, depth of cut, and material hardness. When risk is high, reduce feed rate or depth of cut before running the job.
FAQ
What is chip load and why does it matter for CNC routing?
Chip load is how much material each cutting edge removes per tooth per revolution. Too little causes rubbing and burning; too much causes deflection and broken bits. The ideal chip load for wood is 0.1-0.2mm per tooth; aluminium is much less at 0.025-0.075mm.
How do I calculate feed rate for a CNC router?
Feed rate (mm/min) = RPM x flute count x chip load (mm). For example: 18,000 RPM x 2 flutes x 0.15mm = 5,400 mm/min. The calculator does this automatically once you enter cutter diameter, material, and machine max RPM.
What is the difference between slotting, pocketing, and profiling?
Slotting cuts a full-width slot (hardest on the tool, use 80% chip load). Pocketing removes material with partial-width cuts (standard chip load). Profiling cuts along the outside edge with only one side engaged (easiest, use 120% chip load).