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But the iron is not free to vibrate its full length, only the short 5/16" length or so, as in the op first picture. The cap iron pressing down the iron to the frog at its feet stops vibration to travel up the iron's length.
If the iron is not well seated on the frog's bed, flexing could occur beyond the point where the iron is in contact with the frog.
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I've scanned the patents and there's no mention of the cb's used for reinforcement. Probably not a patentable claim. I don't see a rationale for the thinner irons either, but that would not have been mentioned in the patents either.
Bailey's patent of December 24, 1867 states:
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My object is to use Very thin steel plane-irons, and in so doing I nd that they are liable to buckle under the pressure of the cap, which causes them to chatter, and makes them otherwise imperfect; and my invention consists in the providing of an auxiliary point of contact between the cap and plane-iron, and at the point where the plane-iron tends to buckle or rise from its bed or base, and thus have a pressure at that point in addition to that at the cutting-edge, which firmly holds this thin plane-iron to its bed.
The cap-iron, as commonly constructed, that is, as shown at D, in fig. 3, when applied to the plane-iron E, will rest thereon only at the extreme lower end of the cap-iron, and also at or very near its upper end. There will be a long angular space, between the two irons, when they are clamped together by the holding-devices which are represented in figs. 2 and 3, at A, B, and C, and consist of a screw, A, a bearing, B, and ay cam-lever, C, arranged in a manner well known.
The difficulty experienced from the construction of the cap iron with the single bend a, is, that it allows of vibration of the cap-iron and the plane-iron while in use, such vibration being productive of what joincrs term chattering, and consequent defective operation of the plane.
The cap iron patent claims an improvement from previous cap irons.