This example adds a second value (y) axis to the right side of the specified chart. The second axis uses the same scale as the primary value axis.
Set c = ChartSpace1.Constants
Set axisScale = ChartSpace1.Charts(0).Axes(c.chAxisPositionLeft).Scaling
ChartSpace1.Charts(0).Axes.Add axisScale, c.chAxisPositionRight, c.chValueAxis