Speeds and Feeds Calculator
Calculate Spindle Speed (RPM) and Feed Rate for Milling & Turning
Metric (mm, m/min)
Imperial (inch, SFM)
Spindle Speed:
0 RPM
Feed Rate:
0 mm/min
Cutting Speed (Vc):
0
Understanding Feed Rate and Spindle Speed
In CNC machining, getting your "speeds and feeds" correct is the difference between a perfect finish and a broken tool. These two parameters dictate how fast the tool rotates and how quickly it moves through the material.
1. Spindle Speed (N)
Spindle speed is the rotational frequency of the machine spindle, measured in Revolutions Per Minute (RPM). It depends on the Cutting Speed (Surface Speed) of the material and the diameter of the tool.
- Metric Formula: RPM = (Vc × 1000) / (π × D)
- Imperial Formula: RPM = (SFM × 12) / (π × D)
Where Vc is Cutting Speed in m/min, SFM is Surface Feet per Minute, and D is Tool Diameter.
2. Feed Rate (Fr)
Feed rate is the velocity at which the cutter is advanced against the workpiece. It is usually measured in millimeters per minute (mm/min) or inches per minute (IPM).
- Formula: Feed Rate = RPM × Number of Flutes × Feed per Tooth
Typical Feed Per Tooth (Chip Load) Examples
| Material | Tool Diameter (10mm / 3/8″) | Suggested Chip Load |
|---|---|---|
| Aluminum | End Mill | 0.05 – 0.12 mm |
| Steel (Mild) | End Mill | 0.03 – 0.08 mm |
| Stainless Steel | End Mill | 0.02 – 0.05 mm |
Why Precision Matters
If your spindle speed is too high, the heat generated can melt or work-harden the material and dull the tool. If your feed rate is too slow, the tool will "rub" instead of "cut," causing friction and heat. If the feed rate is too high, the tool will snap under the excessive force (chip load).