and a velocity input which varies with the velocity of tool assembly 19 tool velocity is preferably determined by means of a position encoder 56 which produces an output 58 that varies with the position of voice coil assembly 17 and a tachometer circuit 60 which monitors the position output with respect to time to generate an output signal 61 which varies with tool velocity current i 1 is preferably amplified with amplifier 62 to produce the drive signal for voice coil assembly 17 the present system also includes the weight 39 s voice coil assembly 30 which is driven with a signal 64 provided by a u201c reaction force reduction u201d rfr preamplifier 66 signal 64 is preferably amplified with an amplifier 65 to produce the drive signal for voice coil 30 in order to produce a drive signal which can counter the reaction forces induced by tool assembly 19 rfe preamp 66 receives current i 1 at an input and is arranged to vary signal 64 with i 1 however as noted above when the tool assembly and weight assembly masses are different a drive signal derived solely from i 1 cannot completely counter vibration attributable to the tool assembly 39 s eddy current drag forces countering these drag forces requires that preamp 66 also receive velocity signal 61 at a second input and deriving drive signal 64 from both i 1 and velocity signal 61 when velocity signal 61 and current i 1 are combined in the proper proportions both the reaction force induced vibration of machine frame 10 and the vibration that arises.