Drill Press Speed (RPM) Calculator
Calculate the correct drill press RPM based on drill bit diameter, material type, and cutting speed for clean holes.
Running a drill press at the correct RPM is critical for clean holes, long tool life, and safe operation. Too fast and the bit overheats, dulls prematurely, or grabs the workpiece. Too slow and the drill rubs instead of cutting, causing work hardening in metals like stainless steel.
The Fundamental Formula
RPM = (Cutting Speed × 1000) / (π × Drill Diameter)
Or equivalently:
RPM = (CS × 318.31) / D
Where:
- CS = Cutting speed in meters per minute (m/min), determined by the workpiece material and drill bit type
- D = Drill bit diameter in millimeters
- 318.31 = 1000/π (conversion constant)
Cutting Speed Reference Table (HSS Drill Bits)
| Material | Cutting Speed (m/min) | Notes |
|---|---|---|
| Mild Steel | 25–35 | Most common workshop material |
| Stainless Steel | 10–15 | Use cutting fluid, steady feed |
| Aluminum | 60–100 | Use high RPM, clear chips often |
| Brass | 40–60 | Self-feeding — reduce feed pressure |
| Cast Iron | 20–30 | Dry cutting OK, makes dust not chips |
| Copper | 40–60 | Similar to brass |
| Plastic/Acrylic | 30–50 | Slow feed to prevent melting |
| Wood (softwood) | 50–80 | Can run faster with brad-point bits |
| Wood (hardwood) | 30–50 | Slower to prevent burning |
Carbide-tipped bits can run at 1.5–3× the HSS cutting speeds.
Worked Example
Drilling a 10 mm hole in mild steel with an HSS bit (cutting speed 30 m/min):
RPM = (30 × 318.31) / 10 = 9549.3 / 10 = 955 RPM
On a typical drill press with fixed pulleys, you would select the closest available speed — probably 900 or 1000 RPM.
Feed Rate Guideline
A general rule for feed rate is 0.001–0.003 inches per revolution for steel (0.025–0.075 mm/rev) and 0.003–0.006 inches per revolution for aluminum. In practice on a hand-fed drill press, this translates to slow, steady downward pressure where the drill produces even curly chips — not dust, not large grabbing chips.
Peck Drilling
For holes deeper than 3× the drill diameter, use peck drilling: drill to 1× diameter depth, retract fully to clear chips, then advance again. This prevents chip packing, reduces heat, and extends bit life dramatically.