When trees are cut, pressure and tension are released. These forces lead to one of the most common of all problems facing cabinet and furniture makers---warped planks. Perfectly straight wood is rarely found. And the longer it sits without being used, the worse the warp can get. Woodworkers know how to deal with warps and crowns, which is a springy bow in the plank. It's not that hard if you have a jointer and a band saw. A jointer is a woodworking machine that straightens edges. It has a horizontal knife that the plank slides across. It is used for edge straightening or taking the crown, or "bow," out of planks.
Lay the plank out on a table and examine it. First look for the crown along the edge; the board may have a pronounced "C" shape to it. Lay the chalk line along the outside points of the "C" shape and snap the chalk line in a straight line just skimming the inside of the "C" shape.
Hold the plank up to the band saw, and saw along the line. When finished, set the jointer at 1/6, place the plank on the jointer table on the edge that you just cut, and run the plank through the jointer. Examine the edge; if it's not clean, run the plank through again until the edge is clean and straight.
Lay the plank down on a flat surface; flip it over both ways until the warped middle of the plank is off the floor, the ends touching the floor--the crown is now up. Open the fence of the jointer to approximately 6 inches. Lay the plank on the jointer crown up, like it was on the floor, with the leading edge facing the knife.
Turn on the jointer and ease the leading edge into the knife. As it starts to cut, apply some pressure to the board and continue feeding it through the jointer. When the crown lifts off the knife, keep pushing until the trailing edge of the board begins to cut. Grab a push stick and finish by pushing the plank all the way past the knife.
Repeat pushing the board through the jointer in the same manner, with the crown up; it may take several passes. Each pass will cut more of the crown ends off. Listen to the knife. When the crown is gone, there will be a solid cutting sound the length of the plank. It should now be straight and ready to use.
Always wear safety glasses. Always use push sticks.