Drill Cutting Speed Calculator
Drill cutting speed is the velocity of the drill's outer cutting edge across the workpiece, measured in surface feet per minute (SFM). This calculator pulls Machinery's Handbook values for 11 common materials, applies the standard RPM = (SFM x 12) / (pi x D) equation, and returns spindle RPM for the drill size you enter. Works for both HSS and carbide drills, imperial or metric.
Drill cutting speed formula
Two equations:
- SFM (target cutting speed) is pulled from a material table. Aluminum is 300 SFM with HSS, 800 with carbide. Mild steel is 80 SFM with HSS, 250 with carbide.
- RPM = (SFM x 12) / (pi x D) where D is the drill diameter in inches.
For a 1/4 inch HSS drill in mild steel at 80 SFM: RPM = (80 x 12) / (pi x 0.25) = 1,222 RPM. For a 1/2 inch HSS drill in aluminum at 300 SFM: RPM = (300 x 12) / (pi x 0.5) = 2,292 RPM.
Why drills run slower than end mills
A drill runs at about 75 percent of end-mill SFM in the same material. Three reasons: (1) coolant cannot reach the cutting edge at the tip, so heat builds up; (2) chip evacuation is harder in a hole than on an open face, so chips recut; (3) the drill point has a low relative velocity near the web, meaning the center rubs rather than cuts. All three combine to make drilling hotter than milling at the same SFM.
Drill cutting speed table
| Material | HSS drill SFM | Carbide drill SFM |
|---|---|---|
| Aluminum | 300 | 800 |
| Mild steel (1018) | 80 | 250 |
| Alloy steel (4140) | 60 | 180 |
| Stainless steel | 40 | 130 |
| Cast iron | 60 | 200 |
| Brass | 200 | 400 |
| Titanium | 25 | 80 |
| Plastic | 400 | 1000 |
Handheld drill vs mill drill press vs CNC
The formula does not care about the machine, but your setup does. A handheld cordless drill cannot reach 1200 RPM on a 1/4 inch bit in steel, so drop SFM or use a smaller bit. A benchtop drill press usually tops out at 3000 RPM, adequate for 3/16 and larger HSS drills in steel. CNCs and VMCs can hit 8000 to 20000 RPM, more than enough for small drills. If the calculated RPM exceeds your spindle max, cap it there and accept the lower SFM.
Feed rate pairs with cutting speed
Cutting speed is half of the drilling recipe. Feed rate is the other half, specified in inches per revolution (IPR) and scaled to drill diameter. For a 1/4 inch drill in mild steel at 1,222 RPM with 0.0045 IPR feed, feed rate = 1,222 x 0.0045 = 5.5 IPM. See the drill feed rate calculator for the full feed equation.