Cliff Stamp
BANNED
- Joined
- Oct 5, 1998
- Messages
- 17,562
I had collected a few tension bars to cut up, when I wondered about use as a knife steel. This is a low carbon, unhardened steel, pretty soft, you can bend it readily by hand even though it it a quarter of an inch thick. So as an extreme low end example, I ground a knife blade (~three inches) on one end of the bar. The steel was easily machined, I shaped the basic profile with a 4.5" angle grinder (burning it black intentionally), then refined the bevels and sharpened with a bastard file.
The edge aggression was high, the knife (still attached to the bar) easily cut through fabric (an old sneaker). It was then used for some hacking and grass, weeds and miscellaneous vegetation. The edge was fine, no damage and still aggressive after a few dozen swings. It was then used to cut at some Alders, small woody vegetation, a half an inch thick and under. It easily hacked through the sticks. A piece was then placed on top of a 4x4, and then diced up into sections, trimming off the secondary growth and then moving down the trunk. The edge was still aggressive, no excessive blunting.
The pseudo-spear was then stabbed into the 4x4 a half a dozen times, no damage. It could also break pieces out of the wood on shallow stabs, but on a deep stab (half an inch), the blade bent readily. It worked hardened in that region, as attempting to restore the blade by reverse prying would just bend it in another place. It was restored to semi-straight by beating on it with a hammer. It was then used to split some scrap and clear sticks, which it handled easily, using a framing hammer as a mallet. However during an attempt to split a knotty piece (small stick under three inches), the blade actually bent down under the impacts of the hammer - the split was aborted.
The bevels were then cleaned up with a one inch belt sander, the basic geometry was not altered, just removed the dips from uneven grinding. The edge was also a bit wavy because of all the prying. Checking the edge under magnification revealed a heavy micro-serrated edge, just as would be obtained on a high quality cutlery steel. The edge also scraped shaved a little, and would smoothly slice straight down into a sheet of newsprint. The profile was full convex, very close to flat, no secondary edge bevel, curvature close to the edge (0.024" thick) was 12 degrees per side.
Checking the edge on 3/8" hemp, with a two inch draw, the blade took 30 lbs to make a complete cut. I was a bit rusty not having done this in a while, so a more reasonable estimate would be 25-30 lbs. Considering the waves in the edge, with a clean grind 20-25 lbs should be possible. Anyway, after 62 cuts through the hemp the knife was taking 38-42 lbs, and could no longer slice the newsprint well, was tearing it heavily. Checking the edge under magnification, all the secondary micro-serrations had worn away, but the primary teeth were still visible, and aggression could still be felt on the hemp rope cutting, at least another round (64 cuts) were easily possible before the slipping would become excessive.
For reference, the SOG SEAL with a 600 grit DMT finish took about 40 lbs to make the first cuts, and after only 14 slices on the hemp the force required exceeded 50 lbs. The tension bar knife thus showed much better cutting efficieny and edge lifetime. This shows quite clearly the massive influence that geometry and grit choice for sharpening can make on cutting efficient and edge holding.
The tension bar knife was later sharpened to a high polish using waterstones and finishing with CrO, and it easily shaved and push cut newsprint (it would catch on two sections as I was lazy and didn't reset the edge completely), an argument against another myth about sharpness being a sign of quality.
To clarify, the above isn't an arguement that geometry and proper sharpening are more important that steel quality. They are all important, however it should illustrate clearly that ignoring even one of the aspects can lead to a very poor performance tool, even if the other aspects are very high.
-Cliff
The edge aggression was high, the knife (still attached to the bar) easily cut through fabric (an old sneaker). It was then used for some hacking and grass, weeds and miscellaneous vegetation. The edge was fine, no damage and still aggressive after a few dozen swings. It was then used to cut at some Alders, small woody vegetation, a half an inch thick and under. It easily hacked through the sticks. A piece was then placed on top of a 4x4, and then diced up into sections, trimming off the secondary growth and then moving down the trunk. The edge was still aggressive, no excessive blunting.
The pseudo-spear was then stabbed into the 4x4 a half a dozen times, no damage. It could also break pieces out of the wood on shallow stabs, but on a deep stab (half an inch), the blade bent readily. It worked hardened in that region, as attempting to restore the blade by reverse prying would just bend it in another place. It was restored to semi-straight by beating on it with a hammer. It was then used to split some scrap and clear sticks, which it handled easily, using a framing hammer as a mallet. However during an attempt to split a knotty piece (small stick under three inches), the blade actually bent down under the impacts of the hammer - the split was aborted.
The bevels were then cleaned up with a one inch belt sander, the basic geometry was not altered, just removed the dips from uneven grinding. The edge was also a bit wavy because of all the prying. Checking the edge under magnification revealed a heavy micro-serrated edge, just as would be obtained on a high quality cutlery steel. The edge also scraped shaved a little, and would smoothly slice straight down into a sheet of newsprint. The profile was full convex, very close to flat, no secondary edge bevel, curvature close to the edge (0.024" thick) was 12 degrees per side.
Checking the edge on 3/8" hemp, with a two inch draw, the blade took 30 lbs to make a complete cut. I was a bit rusty not having done this in a while, so a more reasonable estimate would be 25-30 lbs. Considering the waves in the edge, with a clean grind 20-25 lbs should be possible. Anyway, after 62 cuts through the hemp the knife was taking 38-42 lbs, and could no longer slice the newsprint well, was tearing it heavily. Checking the edge under magnification, all the secondary micro-serrations had worn away, but the primary teeth were still visible, and aggression could still be felt on the hemp rope cutting, at least another round (64 cuts) were easily possible before the slipping would become excessive.
For reference, the SOG SEAL with a 600 grit DMT finish took about 40 lbs to make the first cuts, and after only 14 slices on the hemp the force required exceeded 50 lbs. The tension bar knife thus showed much better cutting efficieny and edge lifetime. This shows quite clearly the massive influence that geometry and grit choice for sharpening can make on cutting efficient and edge holding.
The tension bar knife was later sharpened to a high polish using waterstones and finishing with CrO, and it easily shaved and push cut newsprint (it would catch on two sections as I was lazy and didn't reset the edge completely), an argument against another myth about sharpness being a sign of quality.
To clarify, the above isn't an arguement that geometry and proper sharpening are more important that steel quality. They are all important, however it should illustrate clearly that ignoring even one of the aspects can lead to a very poor performance tool, even if the other aspects are very high.
-Cliff
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