Cutting Speed & Feed Calculator (CNC)
Spindle RPM from cutting speed and tool diameter, plus table feed from chip load — the two core machining formulas.
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The Two Formulas Every Machinist Uses
Spindle speed: n = 1000·Vc ÷ (π·D) — cutting speed Vc in m/min, diameter D in mm. A Ø10 mm carbide end mill at Vc = 100 m/min runs ≈ 3183 RPM. Table feed: F = n · z · fz — RPM × number of flutes × chip load per tooth (mm). The same 4-flute tool at fz = 0.05 mm gives ≈ 637 mm/min.
Typical Vc starting points: HSS on mild steel 25-30 m/min, carbide on steel 80-200, carbide on aluminum 200-500, stainless 60-120 with carbide. The tool manufacturer's chart beats any generic value — these are conservative starting points to tune from, watching chip color and sound.
Frequently Asked Questions
What if my machine cannot reach the calculated RPM?
Run at your spindle's maximum and accept the lower effective cutting speed — then keep feed proportional: F = n·z·fz with the actual RPM. Slowing RPM without slowing feed overloads the teeth.
What is chip load and why does it matter?
fz is how much material each tooth bites per revolution (mm/tooth). Too low rubs and work-hardens; too high chips the edge. Typical range: 0.02-0.05 mm small end mills, 0.1-0.3 mm large face mills.
Does the formula work for drilling and turning?
Yes — n = 1000·Vc/(π·D) is universal. In turning, D is the workpiece diameter (it falls as you cut); in drilling it is the drill diameter, with feed given per revolution instead of per tooth.
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Cutting Speed & Feed Calculator (CNC)