Hand Tools Archive

Subject:
Re: Cap iron question-need data *PIC*

mark Hennebury
Hi,
I have a bit of experience with both hand planes and supersurfacers, and as I see it;
there are many wood species they have a lot of variation in structure and properties and respond differently to cutting tools, and therefore require special tool geometry to attain the best cutting results.
A plane blade is a wedge and as such will when planing against the grain, wedge the wood fibers apart ahead of the cutting edge, creating torn not cut fibers. You have several options to prevent this: If you consider first a blade with no chipbreaker. one method is to raise the angle of the blade. A low angle blade creates lots of lift and will easily tear wood fibers.The closer to perpendicular to the plane sole that you have the less lift of the shaving and more forward pushing, or scraping. So a higher angle will be less prone to tearout, but at a price, the price: it requires more effort, the scraping is harder on the blade, and the surface is not that good. The second method is to close the throat opening extremely tight, this would need to be adjustable to suit the size of the shaving and must be precisely matched to the shaving thickness to work. The third method is to use the chipbreaker. The chipbreaker is a misnomer as the purpose is to not break the chip but to put a barrier in place to control the chip from separating ahead of the knife edge,holding the chip under control until is is severed. In this third method you can have a low angle blade and an adjustable chipbreaker. The chipbreaker is adjusted precisely to match the shaving thickness. This method is what was demonstrated in the Kato experiments and is the basis of the supersurfacer design. Another variable is the skewing of the blade to the direction of cut. Skewing does two things, one is to vary the blade angle geometry and two is to cause the fibers to slide along the blade exposing the individual fibers to more of the cutting edge and will sever them much easier, kind of like slicing a soft tomato rather than chopping it. One other variable is to apply pressure at the leading edge of the throat opening to compress the fibers slightly prior to being severed. Supersurfacers have incorporated all of these variables into their design and are capable of producing extremely fine surfaces in a wide variety of wood species.

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