Tooth Impact Frequency

Tooth Impact Frequency is a subject you probably have never heard about before. It is simply the number of times a tooth on a milling cutter impacts the workpiece in a second. It is calculated by multiplying the number of teeth by the spindle speed in revolutions per minute and then divide that by 60. The result is expressed in Hertz (Hz). 

In this example at a spindle speed of 7500 RPM, the two flute endmill has a tooth impact frequency of 250 per second with the six flute having 750 impacts per second. Why is this important? Think of the ruler analogy from a prior post. If you have a very stiff tool vibrating at a very high frequency, the tool with more teeth will give you a better chance to match up the two frequencies (tooth impact and tool point vibration) at a higher speed. Conversely, a tool vibrating at a very low frequency will need more space between teeth to try and maintain a higher speed.