Hmm, I will have to ponder that one a bit. I really wanted to talk to Mike down in Phoenix, but he wasn't there. He will be at our Oregon Woodturning Symposium this coming March, so I plan on cornering him and talking about this.
For now, I will say that for sure, the McNaughton cutting arms get hot when coring. This is not a problem with the Oneway at all. I have 'discussed' this with Kel several times and he does not agree with me at all. The last time I talked to Mike about it, he said, 'Hmm, you might have some thing there'. I now, never touch the blades when I am done coring. Yes they get hot, maybe hot enough to leave a blister if I keep my fingers on it too long. I would have a hard time being convinced that they get hot enough to weaken them to the point of it being the cause of them bending. For sure, with a lot of heavy use, they develop a twist bend in them to the point where the tip can be much lower than the original set height. If you have watched my DVD (now on You Tube), you can see me bend one back straight. So, why does it bend? First reason is there is flex built into the system and blade. This is so that when you have some of those catches, it bends but doesn't break. If you have ever tried to cut off the nub left in the center after you break a core out, when you engage the tip, it drops down as much as an inch on a large bowl. This is because of the flex in the system. So, what generates the heat??? As far as I am concerned, it is because the blade does not run in a true arc all the way to the tip. They are stamped, and because of the flanged tip, the last inch or so of the blade does not fit into the form, and it goes straight. I have checked this out with a number of the blades I have on those big plastic templates with circles up to 20 inch diameter or so). This means that when you are coring, the blade will follow the tip rather than the arc of the blade. When coring small bowls, it isn't as much of a problem. When coring a larger bowl, by the time you get 6 or more inches off the tool rest, you can be off to the side a half inch or so. 1/16 of an inch isn't much on a 3 inch arc, but on an 8 inch arc, it can be a lot. The coring blades ALWAYS drift to the outside of the cut. This means you have a kerf of one arc, and a blade with a slightly different one, and that is why the blade binds in the cut, heat is generated, and you have to open up the kerf some more, either on the top outside, or the bottom inside, so the blade can finish the cut. I do have one blade where I tweaked the tip in a hair, and it actually pulls to the inside of the cut. The Oneway and Woodcut blades are true arcs of a circle. They do not drift or bind when you cut. One of my round-to-it projects will be to make a blade for the McNaughton that is a perfect arc, put a cutter on it and see how true it tracks....
robo hippy
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Originally Posted by Reed Gray
