mark Hennebury
What I did with my old Record handplanes planes in relation to the mouth section of the plane: true up the edge of the throat opening, clean, square and straight.
The leading edge of the throat is pretty much square to the base when i got them, So then I filed it to a steep angle opposite of the blade bed angle from the leading edge of the throat to give as much clearance inside for the shavings, as it gets pretty cramped when you move the chipbreaker up close.
Then honed a small 80 degree flat on the tip of the chipbreaker and moved it up very close to the cutting edge of the blade. Together with the rest of the plane trued lapped and tight. I used a relatively close throat opening and left it set for the largest shaving that i would be doing. The only thing that you have to adjust is the blade depth and chipbreaker when you are cutting different woods and shaving thicknesses. I also hollow ground lots off the sole of the planes leaving a narrow flat strip around the perimeter and in front of the blade. You can hollow grind the soles by hand with a die grinder, you just have to take a few thou off them then lap and polish the sole on a granite plate with a fine abrasive paper of 3M micro film to true and polish it. This reduces friction and increases pressure on the wood fibers just ahead of the blade. You can make most handplanes cut quite well with a bit of tinkering.