Feeds Speeds and Chip Load for Hobby CNC

Why Feeds and Speeds Matter Run a router bit too slow and it rubs instead of cuts — generating heat, burning the wood, and dulling the bit fast. Run it too fast and the load exceeds what the bit can handle — chatter, deflection, or outright breakage. The sweet spot is chip load: the right amount of material removed per cutting edge per revolution. The Chip Load Formula Chip load = Feed rate (mm/min) / (RPM × number of flutes) Chip load is measured in mm — the thickness of the chip each cutting edge removes per revolution. Example: 2-flute bit at 18,000 RPM, 1,800mm/min feed rate: 1800 / (18,000 × 2) = 0.05mm chip load Target Chip Loads by Material These are starting points. Adjust based on what you hear and see. Solving for Feed Rate Once you know your target chip load, RPM, and flute count — solve for feed rate: Feed rate = Chip load × RPM × flutes Example: Target 0.06mm chip load, 18,000 RPM, 2-flute bit: 0.06 × 18,000 × 2 = 2,160 mm/min Depth Per Pass and Stepover Depth per pass (DOC — depth of cut): For hardwood with a 1/4in 2-flute bit, 1.5-2mm per pass is a reasonable starting point. For softwood or MDF, 2-3mm. This is the axial engagement. Stepover: The amount the bit moves laterally between passes during pocketing. Typically 40-50% of bit diameter for roughing, 5-10% for finishing passes. 40% of a 6.35mm (1/4in) bit = 2.5mm stepover. Rule of thumb: Depth of cut rarely exceeds 1× bit diameter for hardwood, 1.5× for softwood. What Bad Cuts Look/Sound Like Burning: Feed rate too low, RPM too high, or dull bit. The chips are too thin — friction instead of cutting. Chatter / vibration: RPM too high for the cutting load, or bit deflecting. Lower RPM or reduce DOC. Rough surface: Too aggressive DOC or stepover. Add a light finishing pass. Bit breakage: Feed too fast, DOC too deep, or incorrect bit type for material. Reduce aggressiveness. Fuzzy exit edge (tearout): Going against the wood grain, or upcut bit on face veneer. Switch to downcut or compression bit for final pass. Speeds for Common Hobby CNC Setups Shapeoko 4 / Carbide Compact Router (65W, 10k-30k RPM) LongMill MK2 / Makita RT0701C (1.25HP, 10k-30k RPM) Tuning in Practice Start conservative. Run a short test pass and listen: Clean, quiet cutting with visible chips: good, you can push feed rate 10-20% High-pitched screaming or whine: reduce RPM or feed Dull thudding or chatter: increase RPM or reduce DOC Burning smell: immediately increase feed or reduce RPM Check chips after the pass. Wood should produce actual chips — not fine dust. Fine dust means chips are too thin — increase feed rate.

Related Guides

Loading_