Replies

1. 
   DonStephan | Jun 07, 2011 08:21pm | #1

   Don't have John White's book at home, so I'm just guessing.  Possible one or more knives are set higher than the outfeed table?  What's been done to the jointer between when it jointed boards flat, and when it made the bow?

2. 
   SteveSchoene | Jun 07, 2011 11:40pm | #2

   If you have knives set too high, relative to the outfeed table you typically get a hollow, not a hump.  You would set the knives slightly  high if you want sprung joints.  The normal setting for straight joints puts the blades a very tiny amount above the outfeed table--about enough to move a straight board a short distance (1/8" say) when the head is rotated by hand.  But if the blades are too low relative to the outfeed table more than a smidge you usually find that the leading edge of the board hangs up on edge of the outfeed table. 

   I suspect you need to work on technique.  The outfeed table is the reference surface.  A down force on the wood should be on the outfeed table as soon as the wood is advanced far enough.  There should be a smooth transfer of force.  Over the infeed table you want to push forward, but not down.  That makes those friction pads on handles often sold as jointer pushers a bad idea.  I use a pusher with a hook that catches the end and allows moving the board with a minimum of down pressure.