Here we show some animations to help understanding of machining vibrations phenomenon

First, a machining vibrates all the time, but most of the time these vibrations decrease naturally. (see animation below)

Under certain conditions these vibrations can spontaneously accentuate.  (see animation below)

All that depends on the passing tooth frequency and the vibration frequency multiplied by one or two or three, etc.

In the following animation, the passing tooth period is a little shorter than two periods of vibrations, the phenomenon is then unstable.

If the tooth passing period had been a little longer than two periods of vibrations, the phenomenon would have been stable, it is simple.

Most of the time, there is a simple rule to use : you have to machine with a tooth frequency slightly lower than the frequency of vibrations. Let us take an example :

Let us consider a 3 teeth tool that vibrates at 1000 Hz.
(you could measure that in a few minutes, very easily).

The rule is very simple :

The first coincidence frequency is : 1000/3 * 60 = 20 000 rev/min
The second frequency is : 1000/3 * 60 / 2 = 10 000 rev/min
The third : 1000/3 * 60 / 3 = 6666 rev/min
etc.

Optimal spindle speeds are a few percent lower than critical speeds, roughly : 19000, 9000, 6000 rev/min.

It is not more complicated than that, do not hesitate to contact us, we can demonstrate this on your own machining processes.