Chatter is visible down to displacements of 10 pin. Achieving displacements below this, even with the most sophisticated hydrostatic wheel bearings, is becoming increasingly more of a challenge as wheel speeds increase. For regular hydrodynamic or ball-bearing-based spindles, some form of dynamic balancer mounted to the machine is essential.
Automatic balancers are mounted on the spindle nose and function by adjusting the position of eccentric weights. Older systems actually pumped chlorofluorocarbon (CFC) gas from one chamber to another, but these have been phased out for environmental reasons. A separate sensor is employed to detect the level of vibration. The wheel guarding may need to be altered to allow a wheel balancer to be accommodated in an older machine. Wheel balancers are standard on the majority of new cylindrical grinders.
Figure 4.3 shows an automatic balancing device incorporated within a conventional wheel mounting arrangement.
The response times of automatic balancers have managed to keep pace with higher speed requirements and many can operate at 10,000 rpm or higher. The range has expanded to cover not only large cylindrical wheel applications, but smaller wheels down to 6 in. for use on multitasking machining centers. Others have the vibration sensor built into the balance head and can also be used as a crash protection and acoustic dress sensor.