Drilling Speeds & Feeds
Calculate drilling RPM, feed rate (IPM), and surface speed (SFM) by material and tooling. Covers HSS and carbide drills for aluminum, steel, stainless, titanium, and more.
Introduction
The Drilling Speed Calculator converts a material's recommended cutting speed into the two numbers a drill press or CNC actually needs: spindle RPM and feed rate. Pick the workpiece material and tooling — HSS or carbide, which differ enormously, e.g. aluminum at 200–300 SFM for HSS but 800–1300 SFM for carbide — enter the drill diameter, and it returns the RPM window, the recommended feed per revolution band for that diameter, and the resulting feed in inches per minute. It replaces the wall-chart-and-guesswork routine with the same speed math used across the rest of this site.
How it Works
Spindle speed comes from RPM = (SFM × 12) ÷ (π × D) with D in inches — machinists know it as the shortcut RPM ≈ SFM × 3.82 ÷ D, since 12/π ≈ 3.82. Feed per revolution is looked up by diameter class, because small drills snap under feeds large drills shrug off: under 1/8 in the band is 0.001–0.003 IPR, rising through 0.004–0.010 IPR at 1/4–1/2 in, to 0.015–0.025 IPR above 1 in. Table feed is then IPM = RPM × IPR at each end of both ranges.
Usage Scenarios
- Drilling 1/2 in holes in mild steel with an HSS twist drill: the 80–120 SFM band converts to roughly 611–917 RPM, bracketing the drill-press speed to select.
- Switching a production hole from HSS to carbide in cast iron and re-running the numbers, since the SFM band roughly doubles.
- Programming a CNC peck cycle: pairing the computed RPM with an IPR from the diameter band to get the feed word in IPM.
- Diagnosing burned drill corners in stainless — the calculator shows the spindle was running at twice the top of the 30–80 SFM HSS band.
- Building a speeds chart for the shop's common drill sizes in aluminum, steel, and titanium.
FAQ
Where does the 3.82 constant come from?
It is 12 divided by π: converting surface feet per minute to RPM requires multiplying by 12 (inches per foot) and dividing by the circumference πD, which collapses to SFM × 3.82 ÷ D.
Why do smaller drills need lighter feed per revolution?
Feed creates thrust, and a drill's resistance to buckling and torsion scales steeply with diameter. A 0.010 IPR feed that suits a 3/4 in drill would snap a 1/8 in bit instantly.
Should I run the top or bottom of the RPM range?
Start mid-range. Favor the low end for rigidity-limited setups, deep holes, and work-hardening materials like stainless; push toward the top with rigid setups, through-coolant, and good chip evacuation.
Do these speeds apply to cobalt or coated drills?
Cobalt (M35/M42) tolerates roughly 10–25% over the HSS figures; TiN/TiAlN coatings add margin too. The HSS and carbide columns bracket the realistic range for most tooling.