I almost had a very discouraging weekend, and I hope somebody can help explain what happened. I had some 4/4 oak to glue up into a 14 3/4" wide by 24 3/4" panel. I had previously flattened one edge of each, then rough cut them to 5 1/2" wide and about 27 " long and flattened one face of each. I then left each board, stickered, to dry and move for two weeks. On Sunday, my plan was to dimension it and glue up the panel.
As I expected, my flattened faces were not flat anymore, having moved a bit on the stickers. The boards had both bowed and crooked. (I think I have used those terms correctly. I mean that if you laid the board face down it made an arch, and if you laid it on edge it made an arch.)
Before I started, I changed my jointer knives. I used a dial indicator, zeroed on the outfeed table, to set the knife height. I couldn't get them to exactly zero, but the total error was on the order of 2/1000". I thought that was good enough.
Then, I just couldn't flatten the boards. I have flattened bowed stock before, and there is a rhythm to it. You hold the board condave side down. As you pass it over the blade, you hear cut-nothing-cut. On each pass, the "cut" phase gets longer as the flat part lengthens, and the "nothing" part gets shorter. When you hear "cut" along the whole length, the board is flat. This time, there were two possible outcomes. Sometimes, it seemed the bow was unchanged and it was cut along the entire length. At other times, I somehow created a concavity (!) that I then had to carefully pare off.
Eventually, I gave up on "flat" (no light visible under my straightedge) and settled on "kind of flat" (small enough errors that I can hand plane and/or sand them away). By that time, I was down to
11/16" thick stock at the narrowest point.I have two questions:
1) Is it possible that somehow in setting my jointer knives, I caused this? I've never used a dial indicator to do it before, so I suspect they were much better set than I have ever managed before, rather than worse. Also, I would understand if improperly set knives meant the stock wasn't coming out *square*. I don't understand how it could cause it not to be flat.2) I have a benchtop jointer. The total length is about 24", with 12" on the infeed side. I know there is a limit to how long a board you can flatten with a given jointer. Is that what happened here? Do I need a new jointer, or at least a longer infeed table? It would make sense that the table was short enough that it could follow the curvature of the stock, but I think I have flattened stock as long as
38" before on the same jointer. The legs for the table I'm working on are from 6/4 red oak, and 30" long, and I had no trouble squaring them.I know it is hard to say what happened if you weren't there, but I hope somebody has some ideas. (The glued-up panel, in case you were wondering, seems to have turned out fine, so I didn't have to start to cry. :))
Ken