Wiley Horne--So. Calif.
Hi Wilbur, Marv, and all,

The thang is, a bench plane has a sole that is wider than the blade. So the rear sole (behind the blade) cannot drop down into the blade's path, because it is 1/4" or so too wide on either side. This leads to some really nasty and predictable consequences--see third paragraph below.

Does that mean you could still have a split level rebate plane? Well, even there, the machine method would only work at a single height differential, say 2 thou, and only if the orientation of the plane remained north/south to within 1/4 thou of true so as not to get outside the blade track, and only if the wood were already pretty flat, etc etc. You couldn't skew the plane for any reason whatever.

Bottom line: A plane which has a high place behind the blade will give the most aggravating and confusing results of any plane. First, it will only make sporadic contact with the wood. Then, when you cantilever the blade down to where you do have contact, the blade will engage for a short time, then bend, flex, or otherwise lose contact, and erupt out of the work causing nasty tearout, and so on down the length of the board.

If it's a single bump in the middle of the plane behind the mouth, the plane will cut on either edge, but not in the middle, which can cause one to imagine that the blade preparation is the problem--belly in the blade somewhere. You can get this effect on low-angle woodies from too tight a wedge (including particularly Japanese planes) , which creates pressure below the wedge fulcrum and makes the sole bulge behind the mouth. So the indications you get depend quite a bit on exactly where the high place is. It's a tough problem to diagnose, if you don't already know about it, which is the reason for my present wordiness.

Wiley