One of the things I do for a living (and have for many years) is machinery vibration analysis. Let's see if I can do this without writing a book.......to keep it simpler, let's confine it to vibrations from the machine itself and exclude external sources.
Some important basics:
1. All rotating machines vibrate.
2. The frequencies of vibration (yes there are more than one) are related to the rotational speed of the machine's components.
For example, with the G0704 these would always include the motor run speed (1XM), gear mesh frequency (GM), spindle speed (1XN) and bearing related frequencies (BSF,BPIR,BPOR), along with naturally occurring harmonics of those frequencies. While cutting there would also be a blade pass frequency (spindle speed x # of teeth on the tool).
Structural resonances can produce local increases or decreases in these vibration levels with no change in level of force in the machine. It's important to distinguish between the presence of large forces (imbalance, misalignment, etc.) and dynamic amplification of the internally generated forces by a structural resonance, because how you address them will be different.
Resonance is simply the natural frequency of a component or combination of components. All structures have a resonant frequency - it becomes a problem when some forcing frequency comes close (+/- 10%) to the resonant (natural) frequency of a structure.
With a variable speed machine you can easily identify a structural resonance by slowly increasing the speed and observing at what speed the vibration is greatest.
Once you have identified that a resonance related vibration is present, there are four ways you can approach it:
*Change the exciting frequency - this is the easiest, change the speed of the machine.
*Stiffen the structure - This method raises the resonant frequency of the structure.
*Add mass to the structure - This method lowers the resonant frequency.
*Add a dynamic absorber to the structure.
I'm sure there will be questions - be advised I'm travelling with limited access to email & will get back to you as quickly as I can.