Calculate spindle speed (RPM) and feed rate (mm/min) based on diameter and cutting parameters.
Understanding Metric Drilling Feed Rates
In CNC machining and manual drilling operations, calculating the correct feed rate is critical for tool life, surface finish, and efficiency. The feed rate determines how fast the drill enters the material. This calculator specifically focuses on the metric system, utilizing Millimeters (mm) and Meters per Minute (m/min).
The Core Formulas
This calculator performs two primary steps to determine the machine settings:
1. Calculate Spindle Speed (RPM)
First, we convert the surface cutting speed ($V_c$) into rotational speed ($n$).
- n: Spindle Speed (RPM)
- V_c: Cutting Speed (m/min)
- D: Drill Diameter (mm)
2. Calculate Feed Rate (mm/min)
Once the RPM is known, we multiply it by the feed per revolution ($f_n$) to get the linear table feed ($V_f$).
- V_f: Table Feed Rate (mm/min)
- f_n: Feed per Revolution (mm/rev)
Typical Cutting Speeds & Feeds
The following table provides general starting guidelines for High-Speed Steel (HSS) drills. Note that Carbide drills typically run at 2-3x these speeds.
| Material | Cutting Speed (Vc) [m/min] | Feed (fn) [mm/rev] (for Ø10mm) |
|---|---|---|
| Mild Steel | 25 – 35 | 0.15 – 0.25 |
| Stainless Steel (304) | 10 – 15 | 0.10 – 0.15 |
| Aluminum Alloys | 60 – 120 | 0.20 – 0.35 |
| Cast Iron | 20 – 30 | 0.20 – 0.30 |
| Brass / Bronze | 35 – 50 | 0.15 – 0.30 |
Material Removal Rate (MRR)
The calculator also provides the Material Removal Rate (MRR) in cm³/min. This metric helps in estimating power requirements and production efficiency. It represents the volume of chips removed per minute.
Example Calculation
Assume you are drilling a 12mm hole in Mild Steel using an HSS drill.
- Cutting Speed: You select 30 m/min from the chart.
- Feed per Rev: You select 0.2 mm/rev.
- RPM Calculation: (30 × 1000) / (π × 12) ≈ 796 RPM.
- Feed Rate Calculation: 796 RPM × 0.2 mm/rev ≈ 159 mm/min.
You would program your machine to ~800 RPM and F159.