Unbalance is a condition that exists when the Mass Axis of a rotor does not coincide with the Rotational Axis.
The result of the conditions listed above create a new center of gravity in the tool holder. This center of gravity can be corrected by adding or removing material from the assembly. To make this correction you need to know the following:
(U = G x 9549 x W) / RPM
Calculation of “G” 2.5 for a #40 Taper Tool Holder Assembly at 8,000 and 20,000 rpm a general
expression for G 2.5 works out to the following:
(U = 2.5 x 9549 x 2.75) / RPM
Solving these expressions for 8,000 rpm and 20,000 rpm range shows:
This shows that as spindle speeds increase the tolerance for allowable unbalance decreases.
There is 2 different types of balancing:
Some manufacturer’s believe a symmetrical design will provide sufficient balance correction. In today’s market with spindle speeds averaging 15,000 RPM’s and higher, Dynamic Balance is required on all tool holders and components to reduce machine tool wear and improve cutting tool performance.
All PIONEER tool holders are symmetrically designed and Dynamically Balanced for optimal performance. Some components like ER Collet Nuts are individually Dynamically Balanced to help eliminate any unbalance effect. This balance will exceed required balance for most machining applications.
For high speed applications, it is recommended to balance the assembly with the retention knob locked in place and re-balance after every tool change. Ultimately this is the only way to guarantee the required balance.