# Cutting Feed and Speed Calculator Cutting feed and speed calculator for milling and turning. Enter diameter, material, and tool material to get RPM, feed rate (IPM or IPR), and surface speed (SFM) in one step. ## What this calculates A cutting feed and speed calculator converts a target surface cutting speed and chip load into the two values a CNC control reads: spindle RPM and feed rate. This one handles both milling and turning, both HSS and carbide tools, and ten common workpiece materials. Feed rate is returned in IPM for milling and IPR for turning, matching the units each operation expects. ## Inputs - **Operation** — options: Milling (end mill, face mill), Turning (lathe) — Milling uses IPM feed, turning uses IPR feed. - **Tool or Workpiece Diameter** (in) — min 0.001 — Cutter diameter for milling, workpiece OD for turning. - **Workpiece Material** — options: Aluminum (600/1400 SFM), Mild steel (100/350 SFM), Alloy steel / 4140 (70/250 SFM), Stainless steel (60/200 SFM), Cast iron (80/250 SFM), Brass (250/500 SFM), Bronze (150/350 SFM), Copper (200/500 SFM), Titanium (40/120 SFM), Plastic (800/1800 SFM) — Material being cut. - **Tool Material** — options: HSS (high-speed steel), Carbide (solid or insert) — HSS is tougher but slower. Carbide is harder and handles 2-5x the SFM of HSS. - **Flutes (milling only)** — min 1, max 8 — Used only for milling. Set to 2 for aluminum, 4 for steel. ## Outputs - **Spindle Speed** (RPM) — Spindle RPM = (SFM x 12) / (pi x D). - **Cutting Speed** (SFM) — Surface feet per minute for selected material and tool. - **Feed Rate** — formatted as text — IPM for milling, IPR for turning. - **Feed Rate (IPM)** (in/min) — Linear feed rate in inches per minute. - **Feed per Revolution** (in/rev) — IPR = IPM / RPM. Used directly on a lathe. ## Details Cutting speed equations - RPM = (SFM x 12) / (pi x D) where SFM is surface feet per minute and D is diameter in inches. For milling, D is the cutter diameter. For turning, D is the workpiece diameter being cut. - Milling feed rate (IPM) = RPM x chip load x flutes. - Turning feed rate is expressed as IPR (inches per revolution), typically 0.005-0.020 IPR. For a 1/2 inch carbide end mill in 4140 alloy steel at 250 SFM: RPM = (250 x 12) / (pi x 0.5) = 1,910 RPM. At 3 flutes and 0.0015 IPT, feed rate = 1,910 x 0.0015 x 3 = 8.6 IPM. For a 2 inch diameter bar of mild steel turned at 350 SFM with carbide: RPM = (350 x 12) / (pi x 2) = 668 RPM. At 0.010 IPR, feed rate = 668 x 0.010 = 6.68 IPM. Why tool material matters The biggest driver of cutting speed after material is tool material. HSS (M2, M42) stays hard up to about 1000 degrees F; above that it softens and wears fast. Carbide stays hard past 1800 degrees F, which is why carbide inserts can run at 3-5x the SFM of HSS. The cutting feed and speed calculator picks SFM from a material table indexed by both workpiece and tool material; a carbide row is always significantly faster than the HSS row for the same material. IPM vs IPR Milling controls program feed in IPM (inches per minute) because the cutter moves through the work at a rate largely independent of RPM. Lathes program feed in IPR (inches per revolution) because the feed-per-rev is what determines chip thickness and surface finish. The calculator returns both so you can paste either one straight into the control. ## Frequently Asked Questions **Q: How do I calculate cutting feed and speed?** A: Start with SFM for the material and tool. RPM = (SFM x 12) / (pi x D). For milling, feed rate = RPM x chip load x flutes. For turning, feed rate = RPM x feed-per-revolution. This cutting feed and speed calculator handles both in one step. **Q: What cutting speed should I use for 4140 steel?** A: Alloy steels like 4140 run at 70 SFM with HSS or 250 SFM with carbide. A 1/2 inch carbide end mill at 250 SFM = 1,910 RPM. For turning a 1 inch 4140 bar at 250 SFM = 955 RPM with a feed of 0.008 IPR = 7.6 IPM. **Q: What is the difference between IPM and IPR?** A: IPM is inches per minute (linear feed), used on milling machines. IPR is inches per revolution, used on lathes because chip thickness is determined per spindle turn. They are related by IPM = RPM x IPR. The calculator returns IPM for milling and IPR for turning. **Q: Does workpiece diameter or tool diameter go into the formula?** A: For milling, the cutter diameter (end mill, face mill). For turning on a lathe, the workpiece diameter being cut, because the cutting speed is the speed at the surface of the spinning workpiece. The calculator labels the input accordingly based on the operation you pick. **Q: Why does the calculator recommend carbide for stainless?** A: Stainless work-hardens under a slow, pressure-heavy cut. Carbide lets you run faster, cut through the work-hardened layer, and use a stiffer tool that resists deflection. An HSS end mill in stainless wears out in minutes. A carbide end mill can last hours at the right feed and speed. --- Source: https://vastcalc.com/calculators/physics/cutting-feed-and-speed Category: Physics Last updated: 2026-04-08