Feed & Speed Planner

Notes for this cut

Getting good results

• Use an air blast. Chips must leave the cut — packed chips mean heat, and heat means a broken or burred tool.
• Ramp into pockets helically at 2–3° rather than plunging straight down.
• If it squeals, or the walls come out shiny and smeared, cut the stepover or stepdown, or drop the rpm and keep the chipload.
• Clamp like you mean it. Good fixturing beats small feed tweaks.
• In plastics, keep chips thick and rpm moderate or the cut will melt.

How this is calculated

Chipload per tooth starts from a material baseline for a 3.175 mm single-flute tool, then scales by diameter, flute count, machine rigidity and the aggressiveness slider.

Feed rate is rpm × flutes × chipload. Surface speed is π × diameter × rpm: divided by 1000 for m/min with the diameter in mm, or by 12 for SFM with it in inches. When the current rpm falls outside the recommended band for the material and tool, a better one is suggested above.

Wood is the exception. Industrial wood cutting speeds run 50–90 m/s, far beyond what a small router bit reaches on a 24,000 rpm spindle, so wood is held to an rpm band instead: bit makers chart it at 18,000 rpm, and Onsrud has you lower the rpm from there until the finish starts to suffer. What matters in wood is the chipload. Wood chiploads come from Freud’s solid-carbide router bit chart, cross-checked against the Onsrud figures ShopBot publishes; wood speeds come from the Leitz Lexicon.

Stepdown and stepover are heuristics expressed as fractions of tool diameter, higher for rigid machines and for side milling.