I have a bowed board that is longer than the infeed table on my jointer. When I pass it over the blades, the lay of the board changes as the board rides up the trailing edge of the jointer infeed table. This is causing uneven planes.
How can I properly joint a piece of wood that is longer than my infeed table?
The solution is to treat the leading and trailing ends of the bowed board like separate pieces. Joint them individually until you can pass the entire board over the jointer without changing the lay.
Make sure your jointer is set up so that it's removing a layer much thinner than the total deviation of the bow in your wood.
Carefully lay the board over the jointer such that the highest point of the bow is approximately over the jointer blades. Since the jointer is removing a much smaller amount than the bowed deviation, the blades shouldn't be in contact with the board. If they are, this is dangerous. You need to reinspect your board to make sure you understand how it's bowed and verify your jointer infeed table is at the proper height.
Pass the trailing end of the board over the jointer as you would normally, taking care to not change the lay of the board when the leading end passes beyond the edge of the outfeed table. You may need an assistant to support the leading end of the board as you do this.
Repeat steps 2 and 3 until you can rest the board on the infeed table and the point-of-contact of the trailing end of the board is jointed and planar.
Pass the leading end of the board over the jointer, stopping halfway down the board at a point where the blades are no longer in contact with the board. Because the trailing contact of the board is jointed and planar, the lay of the board should not change as you pass it over the jointer.
Repeat step 5 about as many times as you jointed the trailing edge of the board. It is ok that the jointed surfaces of the leading and trailing edges of the board are not co-planar.
When you are comfortable with the sizes of the jointed surfaces, you can choose a lay based on either the leading or trailing plane, whichever best suites your project. You should now be able to joint the entire length of the board while maintaining your chosen lay.
It all depends on what you are trying to do.
First if it is really bowed you need to realize that then ends are going to end up much narrower. Set the board with the bow up on a flat surface and measure the highest point of the gap in the middle. The is how much narrower the ends are going to be from the middle of the board. Of course if that is acceptable then you can always straighten out the other side on the table saw.
One way to reduce the narrow ends problem is to shorten the board, cutting it in half will make it much less noticeable. But cutting it down much closer to final length will help, especially if cutting off from the side of the worst offender.
Then you just plane it, run it through and don't try to push harder to get it to plane more, you can make the cut larger to speed up the first few passes, but generally it's not recommended to go more than 1/8" at a time. Each pass will shave off a wider and wider section of the board and eventually they will meet in the middle (or near the highest spot).
Build a temporary extension to the infeed table by supporting a piece of plywood or other suitable scrap on some adjustable height work supports.
