Kunz and Anant both made planes similar to the Harbor Freight #33 and share a #33 as part of the model designation. The Harbor Freight plane is most certainly a clone of the Kunz. The blade adjustment mechanism is similar to the Stanley 151 spoke shave. It is my belief that this design was adopted because of reduced cost of machining and fewer parts when compared to most traditional metal planes.
A chip breaker (or cap iron) performs three functions. In a thin blade it introduces tension that helps prevent chatter, when properly set, can help reduce tear out by forcing the chip, in conjunction with a tight mouth, to sharply curl up against itself effectively snapping the chip so that leverage doesn’t pull up fibers before the edge slices them off, and it allows the depth adjustment mechanism to act upon the blade in most metal planes. In most cases, the cap iron is not set close enough to the blade edge to really be effective at affecting tear out. Using a blade bevel up would prevent the cap iron from being effective at preventing tear out simply because there is no way to set it close enough to the edge, and in fact, bevel up planes tend to be worse for tear out unless the cutting angle has been increased specifically to force the resulting chip up more sharply, thus imitating the action of a high angle frog and/or a properly set cap iron. Bevel up planes have lower bed angles so that the resulting cutting angle will be similar to, or lower than, bevel up planes. That is why properly set up bevel up planes are usually more effective at cutting end grain. If you simply took a blade and turned it bevel up in a standard bench plane you would increase the cutting angle to a very high pitch, effective at preventing tear out when used with a tight mouth but extremely hard to push (there would likely be interference with other parts of the plane also). Lowering of the sharpening angle would then make it easier to use, and would make the edge very fragile and easy to dull. The action of the blade of the #33 design is somewhat similar to any single iron bevel down plane with the “lever cap” holding the blade in the tool and seeming to dampen the vibration (chatter) of using the tool. It is my belief that cap irons first became popular as chip breakers and chatter reducers, became more popular as chatter reducers when thinner blades started to find their way into the market and became almost universally accepted when tool designers started to use them for engaging adjustment mechanisms. Traditional style wooden planes with thick blades often forgo cap irons.
Use of higher cutting angles to prevent tear out is why Lie-Nielsen offers higher pitch frogs for their hand planes, why the low angle bench planes can be adapted for use to prevent tear out and why there has been so much internet buzz on back angles for standard bench planes. For most standard planning “it don’t matter”, but they are all possible solutions for difficult grained woods.
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