a floor preparation machine that uses a number of vertical needles positioned in a tight rectangular pattern . the needles vibrate against the floor surface to prepare the floor surface . the needles are driven by a cam and cam follower . as the cam is turned by a motor , a number of ribs repeatedly contact the cam follower , which in turn repeatedly pushes the needles down . under the top plate that supports the needles , is a rubber form that acts as a “ spring ” to force the needles up after they have been pushed down by the cam follower . in practice , the system produces a sustained vibration of the needles that breaks the surface to a depth of 1 / 16 to ⅛ of an inch .