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 "Testing Blades" by Terry PrimosNOTE:
This describes how I test my knives. Anything and everything in a knife shop is dangerous. These tests can be extremely dangerous and I am not suggesting that you should try it. If you are not an experienced knifemaker, I'll tell you outright, "DON'T DO IT". When I perform these tests, especially the bend test, I have someone near by in case something goes wrong. I also wear eye protection, thick gloves, and a heavy leather apron.
A few years ago I would make knives and give them to friends and relatives to test. There was always that uneasy feeling that I might not have gotten everything right. Would the blade work properly for its intended purpose? Would the edge hold up? Would the knife be able to take much abuse? I was really concerned that I might have to wait a couple of years before any problem surfaced. And during that waiting period, any knives I made had the potential of suffering the same problem.
The solution was quite simple, but it took advice from ABS Master Smith Jerry Fisk to bring the answer to light. Test every blade after heat treating. Use it hard. Occasionally take one to the point of destruction. Then you'll know what your knives will do. Listed below are some of the steps I use.
Standard Tests
1. I have several sections of 2x4 studs with big knots in them stored in my shop. After heat treating, I put a temporary edge on the blade and sharpen it to the point that it will cleanly slice though a cigarette paper. I then hack on one of the knots, working up and down the edge. After doing this I inspect the edge very carefully for damage. The way I resolve any problem with edge damage depends on what the damage is. More information on this follows.
2. If no damage occurred, I check to make sure that the blade will still shave hair from my arm.
3. For larger blades like Bowies and camp knives, I then chop a 2x4 in half twice. Again I check for damage and if none is found, make sure it will still shave hair. It would be easy to cheat, but that would defeat the whole purpose. When checking for shaving sharpness you've got to test the area of the blade that took the most abuse. It's easy to tell. That area will usually have streaks on it from the chopping and/or tiny little pieces of wood on the edge. If everything is okay at this point and the blade is not one to be tested to the point of failure, then the test is finished.
4. Occasionally I will take a blade to the point of destruction to see how tough it is. I do this by clamping 1/3 of the blade in a vise with the tip pointing straight down. I then slip a 3 to 4 foot cheater pipe over the handle. Next I carefully bend the blade. If the blade was differentially heat treated with a hard egde and a spring tempered spine, it should bend to 90 degrees without breaking. Otherwise the blade should not fail until it has been bent approximately 45 degrees. The cheater pipe is not just to get me a little farther from the blade, it is also for more leverage. Unless the blade was forged pretty thin, I can't bend it 90 degrees or break it by hand.
Other Tests
A good test for a blade is cutting rope. Rope cutting can wear down an edge pretty quick. One of the performance tests for a prospective ABS Journeyman or Master Smith is to cut a one inch free hanging sisal or manilla rope in one movement. I have stretched a piece of rope across a board and cut it up like a piece of sausage on occasion. Cutting up cardboard boxes is another good test. I've also been known to hack a limb off a tree every now and then.
Reading the Edge
Sometimes damage may be obvious. Other times there may be some type of damage that doesn't really jump out at you. This is how I inspect for damage. First I look all over the edge with a magnifier. I use an opti-visor like you might see a jeweler wear. I will also very gently, carefully, and slowly drag the edge across the edge of a fingernail. Any catching or snagging can indicate a chip in the edge. A sort of slip or small bumping feeling can indicate a flat spot in the edge. A good (and safer) way to find a flat spot is to take the knife out into the sunlight. Hold the blade edge up. Slowly rock the blade and look for a shiny little glimmer in the edge. A flat spot, no matter how small will reflect light like a facet on a diamond.
Fixing Problems
A chipped edge means the blade was not drawn back enough after hardening. If this ever happens, I take the blade back to the draw (tempering) phase to remove more of the brittleness. I keep records of the hardening and tempering temperatures that I use for various types of steel. The only time I really have this problem is when experimenting with a new type of steel.
A flat spot in the edge means it was drawn back too much. To fix this I would have to go all the way back to the hardening phase. Again, because I keep records of successful heat treat temperatures, I seldom have to deal with this unless experimenting with a new type of steel.
If the edge has just a tiny little crinkled look, then the edge is just a bit too delicate. This is an easy fix. I just beef it up some at the grinder and try again. Now understand, when I say tiny little crinkled edge I do mean tiny. If it looks like a hacksaw blade, I've got a problem. I would go back to the hardening phase.
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