The cast aluminum base had a hump in the casting 90 degrees to the plunge travel.  Don't expect to get good results with a tool that references the base to a flat surface when the tool rocks back and forth on its base.  Yes the issue can be resolved with enough elbow grease.  Just apply spray contact adhesive to the back side of coarse grit sandpaper,and stick it to the flat surface of a cast iron jointer table.  Then rub it flat, and reattach the somewhat less than sturdy aluminum base plate.  I just don't like having to do makeshift finishing work on a poorly manufactured tool.  And no, I didn't send it back for an exchange (not purchased from Amazon).  It only took the better part of one day to flatten the base.  It would have taken two weeks for an exchange, which may or may not have been from the same production run with the same exact issue.  Who knows?