DennisCA":2nqj2f4n said:
About getting the cap irons flat to the blade, I've been told that the common method of using a flat surface and making the cap iron itself a truly flat surface is incorrect. The reasoning is that once you tighten that screw the cap iron will bend slightly and you won't have a perfect contact surface anymore. The method I was told use layout fluid to see where the cap iron makes and doesn't make contact when tightened, then keep honing and tuning very, very finely until the contact surfaces mate perfectly.
Dennis, I think you're spot on with your point about cap-iron deflection when the cutter and cap-iron are screwed together. However, I think there's another factor often forgotten, and that's the extra deflection applied by the lever cap (or wedge in a woody) when the cutter and cap-iron are locked into the plane. That pressure, applied to the top of the cap-iron hump, will deflect the cap-iron leading edge forwards, and bend it slightly so that if the cap-iron fits exactly to the cutter back along the mating surfaces, a tiny bird's-mouth will open, and that will obviously fill with shavings and clog the plane to a standstill at the first use.
That deflection under lever-cap or wedge pressure will depend on how thick the cutter and cap-iron are; thicker components are stiffer, and in consequence will deflect less. Thus, the iron and cap-iron in an old woody won't deflect much at all, but the thin cutter and bent-metal cap-iron of a standard Bailey type plane will deflect quite a bit. That will influence two things. Firstly, how much clearance is needed behind the leading edge of the cap-iron to get a true seat in working condition (not out of the plane), and also how close the cap-iron has to be set to the cutting edge to get the 'cap-iron' effect. The thick, heavy iron and cap-iron from a vintage woody will need the cap-iron pushed a small fraction of a millimetre from the edge. So will the thick irons and cap-irond of most modern premium planes. The cutter and cap-iron pair from a standard Bailey plane will need to be set a bit further back to allow for the deflection as the lever-cap pressure comes on.
Maybe rather than worry about measurements, the pragmatic way of getting used to setting up a smoothing plane to get good cap-iron effect is to set it somewhere, try it, reset, try again, and so on. Once you have the set you feel is best, make a mental note of the gleam of light between cutting edge and cap-iron leading edge, and aim for that every time - with THAT PARTICULAR iron and cap-iron. The gleam might well be different for a another double iron pair in a different plane. I'm pretty sure that's how the craftsmen of old went about it - if you'd started talking thous or fractions of a millimetre to Charles Hayward, he'd probably have looked very blankly at you, but he could certainly set up a plane.
