The cutting tools catalogs or our experience tells us the SFM (Cutting Speed) we need to use for a given application. On the other hand, the CNC machine is programmed with the RPM (Spindle speed). Therefore it is common that we need to compute the RPM from a given SFM either for programming or to ensure that the SFM we want to run at is within the machine’s limit. It is calculated by dividing the cutting speed by the cutter’s circumference.

## SFM to RPM Formula

• d – [Inch]
• n – [RPM] (Revolutions per minutes)
• Vc – [SFM] (Surface feet per minute)

$$\large RPM = \huge \frac{1000 \times SFM}{\pi \times d}$$

## SFM to RPM Chart (Inch)

Find the required RPM according to your tool’s diameter and SFM

## SFM to RPM Chart (Metric)

Find the required RPM according to your tool’s diameter and SFM

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