Spindle Speed Calculator

Created by Rahul Dhari
Reviewed by Steven Wooding
Last updated: Dec 16, 2021

The spindle speed calculator will assist you in determining the appropriate speed and feed rates to perform any lathe or milling operation. These heavy-duty machines are the backbone of the manufacturing industry and are used for material removal processes such as turning, facing, milling, finishing, knurling, grooving, etc.

To perform said operations, they must operate on the right spindle speeds as well as feeding rate to maintain dimensional accuracy of the workpiece and finished product. The article explains what spindle speed is and how to calculate spindle speed and the feed rate calculation. After the example exercise, you'll be able to calculate spindle speed for milling or lathe operations.

What is spindle speed? What is feed rate?

The spindle speed is defined as the rotational speed of the spindle of the machine. In lathe or CNC machines, the workpiece is attached to the chuck, which is attached to the spindle. Apart from the lathe, the spindle holds drill bits in the chuck, grinding wheels, and milling or shaping tools. The tool would get regular wear and tear from its interaction with the workpiece during the material removal process. The spindle speed affects the surface finish of the workpiece and also the longevity of the cutting tool.

The spindle speed Ns, in rpm, for a machined operating at cutting speed V, in m/min, is given by the spindle speed formula:

Ns = V * 1000 / (π * D)

where D is the diameter of the workpiece in mm. The above equation is used to calculate spindle speed for milling or other material removal processes. The spindle speed also affects the feed rate Fr, in m/min, for the machining operations. The feed rate is defined as the amount of material being fed into the tool in length per unit time. The feed rate calculation formula for a machine having Z teeth is given by the equation:

Fr = Ns * Ft * Z

where Ft is the feed per tooth in mm.

How to calculate feed rate and spindle speed?

To calculate spindle speed:

  1. Enter the diameter of the part, D.
  2. Fill in the cutting speed, V.
  3. The CNC spindle speed calculator will return the spindle speed.

To calculate feed rate:

  1. Enter the number of teeth, Z.
  2. Insert the feed per tooth, Ft.
  3. The spindle speed calculator will return the feed rate.

Example: Using the spindle speed calculator

Find the spindle speed for milling a steel workpiece having a diameter of 20 mm. Take cutting speed V to be 5 m/min. Also, determine the feed rate for a single tooth having feed per tooth of 10 mm.

To calculate spindle speed:

  1. Enter the diameter of the part, D = 20 mm.
  2. Fill in the cutting speed, V = 5 m/min.
  3. Using the spindle speed formula:
Ns = V * 1000 / (π * D)
Ns = 5 * 1000 / (π * 20) = 79.58 rpm

The above paragraph explains how to calculate the feed rate for milling. To use the feed rate calculation formula:

  1. Enter the number of teeth, Z = 1.
  2. Insert the feed per tooth, Ft = 10 mm.
  3. The feed rate is
Fr = Ns * Ft * Z
Fr = 79.58 * 0.01 * 1 = 0.7958 m/min


How do I define spindle speed?

The number of rotations per minute for the spindle is known as the spindle speed.

How do I calculate spindle speed?

To calculate spindle speed:

  1. Multiply cutting speed by 1000.
  2. Divide the product by the circumference of the workpiece/tool.

What is feed rate?

It is the rate at which the workpiece is fed into the tool or vice versa. It is measured as the length of the workpiece per time.

How do I calculate feed rate?

Feed rate can be calculated by:

  1. Multiply the number of teeth with the feed length per tooth.
  2. Multiply that product by the spindle speed.
Rahul Dhari
Diameter of part (D)
Cutting speed (V)
Number of teeth (Z)
Feed per tooth (Fₜ)
Spindle speed (Nₛ)
Feed rate (Fᵣ)
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