Tips on machining vol.2
Suppressing chatter in long-workpiece machining on turning center
－How to cut long and thin workpieces－

Chatter generated when a long workpiece is machined on a turning center is one of the common problems facing many machinists. The cause of chatter varies. Although in some cases it is difficult to identify the cause and find a solution, chatter is largely due to thrust force (a force that is applied on the workpiece in a direction perpendicular to the surface), which causes the workpiece to be bent. The bent workpiece then tries to return to its original shape. The repetition of bending and returning to the original shape generates chatter. In other words, the factors contributing to chatter are “thrust force” and “workpiece deflection (bending).” This indicates chatter can be suppressed by reducing the thrust force or preventing the deflection of a workpiece on which thrust force has been applied.

There are two ways to reduce the thrust force: one is reducing the thrust force itself, and the other is generating the countervailing force to offset the thrust force.
Thrust force in general can be reduced by changing cutting conditions (e.g. lower the rotational speed of workpiece, reduce the depth of cut) or by changing the tool tip and holder specifications (e.g. widen the rake angle (breaker)).