Stephen Tashiro
07-24-2009, 1:57 PM
I find the typical diagram of the jointer/planer's princple of operation rather silly. It shows in cross section how a flat board passing over the jointer/planer can be made flat. From the point of view of this diagram it doesn't matter if you press the board down on the out-feed table or the in-feed table. It should rest squarely on both - in theory.
In practice, you might have something like a 6 ft pine 2x4 from the hardware store. It will be bowed. Suppose you put it on the board down on the bed so the highest part of the bow is in the middle. When you start to feed it you will plane off some of the leading end. Then the bow will take over and raise the board above the cutter head in the middle. At the trailing edge you do some planing, but usually not as much as at the leading edge. The pure geometry of the situation is complicated. You have an arc moving over two tables that are at different levels. The motion of the arc depends on where it touches so the length of the tables does matter.
I'm sure there are as many ways to use jointer/planers as their are operators. But have any of these operators produced realistic diagrams to show their actual procedures?
I find it simplest to mark a line that shows how much of the bowed ends of the board needs to be taken off. Then I make partial passes to cut to that line. Often I hold the back end of the board slightly above the level of the in-feed table as I start the cut. I alternate which end of the board is the leading end until I get to the stage of a final few passes, when the idealized geometric theory shown in books actually applies.
In practice, you might have something like a 6 ft pine 2x4 from the hardware store. It will be bowed. Suppose you put it on the board down on the bed so the highest part of the bow is in the middle. When you start to feed it you will plane off some of the leading end. Then the bow will take over and raise the board above the cutter head in the middle. At the trailing edge you do some planing, but usually not as much as at the leading edge. The pure geometry of the situation is complicated. You have an arc moving over two tables that are at different levels. The motion of the arc depends on where it touches so the length of the tables does matter.
I'm sure there are as many ways to use jointer/planers as their are operators. But have any of these operators produced realistic diagrams to show their actual procedures?
I find it simplest to mark a line that shows how much of the bowed ends of the board needs to be taken off. Then I make partial passes to cut to that line. Often I hold the back end of the board slightly above the level of the in-feed table as I start the cut. I alternate which end of the board is the leading end until I get to the stage of a final few passes, when the idealized geometric theory shown in books actually applies.