Wulf, I always get in trouble when I answer this question. I have my way of and reasons for doing what I do, and it's not that I think my way is the only way. My goal in making blades, since I particularly like to make large blades, is to make them as light and well balanced as possible. The deep hollow grind allows me to achieve that, and I make allowances for the fact that a hollow ground blade is not always the best chopper, but it can be a very good chopper. I would not use either of these on wood. Frankly I can edge an Ontario machete so it will cut wood better than these.
That said, here's what's going on in these blades. On both blades these steel is about 3/16", maybe a little less. The spine however maintains that full thickness to within about 3-4" of the point, retaining strength along the blade's entire length. This differs from a flat ground blade that uses a distal taper, so that while it might be 1/4" at the guard, it could be under 1/8" long before it gets to the point, so the forward third of the blade would actually have less strength than what you see here.
Between the spine and the edge, the steel doesn't do much. Most of it is weight, so I remove as much as possible. At the edge, I allow the steel to flare back out, so the blade is actually thicker there than it is 1/2" higher. I then apply a wide convex (parabolic) edge that gives you the cutting qualities of the convex grind, but without the weight and just as importantly without the drag it would create as it moved through the material being cut. Basically what I create is a convex blade without the mass of steel that's normally in the middle of it. The convex edge extends up anywhere from 1/8" to 1/4", and is rounded over at the top to give it the same ballistic qualities as a boat tail bullet.
Other attributes of this grind include the fact that the hollow grind is a natural stiffener, working like a large fuller. It's basically an arch, and arches don't like to bend, so even though the blade is light, it is not whippy. Such bend as there is in the blade is uniformly distributed along the entire length of the blade, so no one area is getting overstressed while another remains rigid. The grind is angled so it thins naturally and gradually as it approaches the point, but still leaves enough steel at the point so that is not weakened. The point is actually an extension of the spine.
The angled edge on these blades serves to enhance penetration in a chop against tactical targets. It acts like a giant serration, also providing a rapidly changing angle through a slashing cut to improve cutting efficiency.
Can a hollow ground blade cut? One of my CPM-3V espadas was reviewed about a year ago and successfully cut through a 12" thick shank of beef, edge to edge and through 3" of very dense bone without any trouble. The bone was cleanly cut without any evidence of splintering. The same sword also sliced through 3" of dried bamboo, also without splintering the wood.
My take on this is that we have available to us today equipment that allows us to do things our ancestors couldn't. I try to use that equipment to best advantage. We also have some great new steels, e.g. CPM-3V, that are tougher than anything our ancestors ever dreamed of. These steels allow us to make blades that are thinner, faster and more efficient without sacrificing strength or durability. This is a very new thing. 3V has only been around a couple years. I'm just trying to use it to its full potential.
Thanks for the nice comments folks. We knifemakers work alone so the only way we know that what we do is worth the time is to get feedback from those who know and care about blades. It's deeply appreciated.
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