...thats a Following Error problem. If, this machine has the DC Servo Dynamics Amp's/Drive system locate the Y Axis board and look for the "Signal or Gain" Pot and try adjusting it 1/4 to 1/2 a turn CW (more gain).\
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The above would be a quick test if, the Gain adjustment is borderline. Other issues maybe causing your problem like dirty Motor Tachometer. A sign of a dirty Tachs is rough or jumpy axis when moving.