Not so long ago Barry described having a problem with a twisted drawer. I was too busy at the time to share how I deal with twisted boards. But first, let me just say that while it may not seem like much if there was say 1/16" twist in all the sides of a drawer, it all adds up. For instance lets say the drawer is 2' x 2', that is 8' total length, so thats 4/16" or 1/4" that one corner will be up when the other side is flat on the table.
What I do, is to set the board on the infeed bed of my jointer to see which corners are holding it up. If I hold one end down flat against the table, then find at the opposite end has one corner 1/8" space under it, the best approach is to take half that off both ends. Then when it goes through the thickness planer only the opposite corner will need a 1/16" to be parallel.
However if you hold either end flat letting the other be up 1/8", then the opposite face will need 1/8" to get it parallel, for a total of 1/4" reduction in thickness from the beginning thickness.
Now for technique, for longer than I care to admit I would use tiny wedges to hold the trailing end up to split the difference while feeding the board across the blades. Finally one day it dawned on me that there is a much simpler way. First, I always sight down ever board to see what else might come into play such as bow, then turn the crown side up. I then carefully set the board down starting in the middle, pressing the middle flat down on the outfeed, while feeding with my trailing hand pressing down over the corner that is against the table letting the high corner stay at the same height off the table. If it was 1/16" and my blades are taking 1/16" it will be flat from the middle back. Then turn the board end for end and do the same. Sight the board again. If there was some bow it will likely still be there so I may start in the middle again, unless its a small amount that would be gone if fed end to end.
I would imagine some of you will shutter thinking this is a dangerous trick if you have never started in the middle, but if the outfeed table is set appropriately there isn't enough blade above the table to catch. Oh, I always start by setting the trailing end down first and apply pressure while bringing the board down.
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- How I remove twist on my jointer.