Q:  Is mounting my calibration shaker on the work bench a bad idea?

A:  Depends on your bench! Some rigid support benches are fine. Do a test sweep with a triaxial accelerometer mounted and look for resonances and frequencies showing transverse motion. In general, it is safest to move the shaker to an "elephant's foot" (a structurally rigid, solid pedestal) to reduce bench resonances and also place the excitation device at an ergonomically desirable height and location for the operator.