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Posted: 9/11/2002 10:38:47 AM EDT
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As stated earlier in the series, I test each blade after the tempering process. I don't even clean off the oxides from the tempering process. A temporary edge will be placed on the tempered blade and a series of tests will be performed. If something didn't quite turn out right and I had already put the final finish on the blade, then I've wasted all that time. In this segment I'll be showing different knives. I use a variety of tests. But they all start out the same way. Here is a shot of me putting a test edge on a small hunter-sized blade, and a large Bowie. http://home.sport.rr.com/primos/knifemaking/rolling-edge.jpg http://home.sport.rr.com/primos/knifemaking/rolling_edge.jpg In both a cases I am putting what is known as a convex edge on the blade. I have chosen an area behind teh top contact wheel of my grinder. It's called slack belting. By using the slack portion of the belt I am creating a natural convex shape. Convex edges are quite strong because the edge has a lot of support behind it. Another plus is that convex edges are more streamlined than a common factory type edge which has two flat planes converging to a point. There is less drag on the cut with a convex edge as well. To check the keeness of the edge, I'll start with slicing thin strips of paper. In the following shot I just tore a page out of a catalog -- apologies to A.G. Russell -- if he sees this, I may not get any more catalogs. http://home.sport.rr.com/primos/knifemaking/paper-slice.jpg An even better thing to use is plain old newsprint paper. In this case, the catalog was what I had handy. To really push it, you can try a cigarette paper. That's a real booger because it's so thin, light, an delicate. http://home.sport.rr.com/primos/knifemaking/cig_paper_slice.jpg With both of these tests the paper is held out in front of you. On the larger paper you would make thin slices down the paper. You want a clean slice with no snagging along the way. On the cigarette paper you try to make a clean slice through the paper with no tears. Another good test is to hold up a roll of toilet paper with a couple of sheets hanging down from the roll. You swat at the free-hanging sheets with the knife edge and look for a clean cut. If the keeness is not there, the sheets will tear out in a "V" shape. |
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Okay, we can get the puppies sharp, but will the edge hold up? On the smaller knives I'll find a board with a nice hard knot in it, then hack a bit on that knit and check the edge for damage. http://home.sport.rr.com/primos/knifemaking/pine-knot.jpg After doing this, I check the edge for the following:
On the larger knives I'll get a little tougher and chop up the board. http://home.sport.rr.com/primos/knifemaking/2x4_chop.jpg Another thing that is tough on edges is cutting sisal or hemp rope, cutting up cardboard boxes, hacking a limb off a tree, etc. A new test I've incorporated is a tip strength test. On really thin blades used for intricate work, there's not a whole lot of use for this test. But on a general purpose knife it's a good idea. http://home.sport.rr.com/primos/knifemaking/tip-test.jpg For this test I just gouge out a piece of wood with the tip. Okay, everything has gone well. There's no damage, but will it still cut? To finish up I check to make sure the knife will still shave hair. http://home.sport.rr.com/primos/knifemaking/shaving.jpg I also periodically do destructive tests. For fully hardened blades, I'll see hwo far they'll go before breaking, then check the grain inside. What I am looking for is a smooth, silky matte gray texture. This signifies a nice fine grain structure. An overheated piece of steel with large grain will look rough and sparkly sort of like grains of sugar. On differentially heat-treated blades with a hard cutting edge and a softer, tough spring tempered spine, I do the 90 degree bend test. http://www.primosknives.com/gallery/bendtest.jpg Hopefully the blade won't break. I never guarantee that a blade absolutely won't break, and I hope to goodness that folks don't ever use my knives for a pry bar. I try to push them farther than what the "average" user will do, just to have peace of mind and confidence that I'm making a quality product. When someone wants a knife to cut open 50 gallon drums, cut through car doors, hack on cinder blocks, drive the tip though plate steel, and any number of other extremely abusive things I've seen advertised, I suggest that they find another maker. My customers aren't looking for an indestuctable piece to abuse. They are looking for a good quality handmade knife designed for a specific purpose. They like the idea that their knife was made just for them, and that I've spent days working on and examining every square inch, and putting heart and soul into the project, and testing along the way. Since the knives are hammered to shape, and not cut out from a pattern, with no use of CNC machines, etc., no two are exactly alike. There aren't thousands of them pumped out in assembly line fashion, and there are no pre-manufactured parts. Each one has its own character. |
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