Plunge Feed Rate Calculator
Optimize your CNC Z-axis entry speeds
Values calculated in Units per Minute (Inches or Millimeters based on input).
Understanding Plunge Feed Rates
In CNC machining, the plunge feed rate is the speed at which the cutting tool enters the workpiece along the Z-axis (vertically). Unlike horizontal milling, where the tool engages the material from the side, plunging puts significant axial stress on the tool and the spindle.
How the Calculation Works
The plunge feed rate is typically derived as a percentage of the calculated horizontal (XY) feed rate. The formula used by this calculator is:
- Horizontal Feed Rate (F) = RPM × Number of Flutes × Feed per Tooth
- Plunge Feed Rate = F × (Plunge Factor / 100)
Recommended Plunge Factors
The appropriate plunge factor depends heavily on the tool geometry and the material being cut:
| Tool Type | Recommended Factor |
|---|---|
| Center-Cutting End Mill | 50% of XY Feed |
| Non-Center-Cutting | Use Ramping/Helical instead |
| Soft Materials (Plastic/Wood) | 50% – 100% of XY Feed |
| Hard Metals (Steel/Stainless) | 25% of XY Feed |
Practical Example
If you are using a 2-flute end mill in aluminum at 8,000 RPM with a recommended chip load of 0.003″ per tooth, your horizontal feed rate would be 48 inches per minute (IPM). If you apply a standard 50% plunge factor, your Plunge Feed Rate should be set to 24 IPM to prevent tool deflection or breakage upon entry.