Enter the surface speed (cutting speed) and diameter into the calculator to determine the rotational spindle speed.
Spindle Speed Formula
The following formula is used to calculate the rotational speed of a spindle.
SS = CS/(PI*D)
- Where SS is the spindle speed in rotations per time
- CS is the cutting speed.
- D is the diameter.
To calculate the spindle speed, divide the cutting speed by the result of pi times the diameter.
In this case, the formula will work for any units as long as they create a rotation per unit time. However, this is often simplified to the following formula:
SS = 3.82*SFM/D
- Where SFM is the cutting speed in surface feet per minute
- SS is in RPM
For the first equation, to make the units equal RPM, make sure the CS is in the distance per minute and the diameter is in the same units as the distance in cutting speed. For example, if the CS (surface speed) is 50ft/min, then the diameter should be in feet.
Example Problem
How to calculate spindle speed?
First, determine the surface speed, also known as cutting speed. For this example problem, the surface speed is determined to be 5000 feet per minute (ft/min)
Next, determine the diameter of the spindle. The diameter of the spindle is measured to be 18 inches. Since the units should match the surface speed-length unit, divide by 12. This yields 1.5 ft.
Finally, calculate the spindle rotational speed using the formula above:
SS = CS/(PI*D)
= 5000/(3.14159*1.5)
= 1061.33 RPM.
FAQ
What is surface speed in machining?
Surface speed, often referred to as cutting speed, is the speed at which a cutting tool passes over the surface of the workpiece it is cutting. It is usually measured in feet per minute (ft/min) or meters per minute (m/min) and is a critical factor in determining the efficiency of the machining process.
How does the diameter of a spindle affect its rotational speed?
The diameter of a spindle directly affects its rotational speed (RPM) because, according to the spindle speed formula, the rotational speed is inversely proportional to the diameter. This means that as the diameter increases, the rotational speed decreases, and vice versa, to maintain a constant cutting speed.
Why is it important to match the units when calculating spindle speed?
Matching the units in the spindle speed formula is crucial to ensure the accuracy of the calculation. Since the formula involves dividing the cutting speed by the product of pi and the diameter, having mismatched units (e.g., feet for cutting speed and inches for diameter) would result in incorrect calculations of the spindle speed in rotations per minute (RPM).
