It sounds like the sole is not flat. It could be either concave or convex. Convex is easier to fix if you feel like making the effort. For a #6, it really only needs to be flat around the perimeter and the area just in front and behind the mouth. If the rest is hollow, no big deal. Also make sure the mouth opening is smooth and free of burrs.
You can lap and polish the sole all you want but really, for a foreplane, you don't need to make it into a mirror.
The blade is more important on a foreplane. I've got the blade cambered on my 5, 6 and 7. This helps take a more aggressive shaving without digging in at the corners. On my #6 and #7 the camber is maybe such that the corners are back a little less than 1/32" from the center. That's enough to see a strong wedge of light when holding the blade and a square into the light.
Don't try setting the blade depth by eye. That's a waste of time. You can adjust out most of the skew by eye, sighting down the sole and slowly bring out the blade. Use the lateral adjuster to level the blade then slowly retract it again, still sighting down the sole. You should see the little black line disappear evenly. Again, use the adjuster to correct. Final lateral adjustment is done after you get a shaving to appear. Just nudge the lever over toward the heavy side and center the shaving. If the cap screw and cap iron are tight, the lever will hold. How tight? Depends on personal preference, I go for "need to squeeze pretty hard to lock the cap iron" tight. If you can close it by hitting it with a pillow, too loose. If you need an eight pound sledge, too tight.
With the blade fully retracted, take a test swipe. No cut, extend the blade just a 1/4 turn or less. Test cut and repeat. If you go too far, retract the blade but remember to advance the nut again to remove the backlash. Otherwise the blade will push back up with each pass.
Wax the sole with some parafin wax and have at it.
A #6 isn't intended to take ultra fine shavings (but you can) so having a slightly more open mouth is OK. Its intended to take some rather aggressive shavings. And even though it can take rank shavings, with a sharp blade, you shouldn't need much downward pressure. Just a little more than the weight of the plane does the work.
Last edited by rwyoung; 05-14-2010 at 12:19 PM.