CNC RPM Calculator (SFM to RPM Conversion)

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What is RPM in CNC machining?

RPM (Revolutions Per Minute) determines how fast the cutting tool rotates. It is calculated using Surface Feet per Minute (SFM) and tool diameter.

Using the correct RPM is important for tool life and surface finish. Higher RPM is used for softer materials like aluminum, while lower RPM is used for harder materials like steel.

Example:

If SFM = 300 and tool diameter = 1 inch, RPM ≈ 1146.

When to use this calculator:

Use this calculator when determining the correct spindle speed for a given tool diameter and cutting speed.

Machining tip:

Always adjust RPM based on material type—higher RPM for aluminum and lower RPM for harder materials like steel to improve tool life.

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