Based on favorable results from a knife made from a piece of tension bar another blade was ground thinner to increase the cutting efficiency, and had an extended handle to increase chopping ability. The blade thickness was 0.0105", just over 3/32", with a 9.5 centimeter sharpened edge, and a total length of 32.5 centimeters. The knife weighed 180 g and the balance point was five centimeters in front on the center of the index finger.
Based on the performance of the last knife, it was hoped that this knife would reach at least 254 cuts, with 510 being maybe probable. Two runs were made, the edge left with the finish of a 100 grit AO belt (fresh). The micro-teeth were large (~225 microns deep) and crisply formed. The first run was at an edge angle of ~10 degrees per side. The first slice was very aggressive, the knife bit in cleanly and only required 12 lbs on the draw, a massive improvement over the previous tension bar knife. However blunting was very fast, and after 6 cuts no aggression was left.
After the first two cuts the edge was checked under magnification and the wear was significant, large smooth regions were present. After six cuts the deformation was large enough to be seen by eye, the entire edge collapsed in the contact region, 0.3 to 0.4 milimeters deep. The second trial was done with an even more acute edge, seven to nine degrees per side. The aggression was very high on the start of the cut, but the edge again collapsed and this time not even one cut could be made. In contrast, D2 blades have been taken down to even thinner and more acute edges with no such problems slicing hemp.
The edge was modified with the application of a secondary bevel, ~15 degrees per side formed with waterstones. The knife was 0.005" thick at the back of the edge. An additional micro-bevel was formed at 22 degrees per side with a fine ceramic rod. The tension bar knife was used on the kitchen on various foods. On thick binding foods like turnips, the cutting ability was significantly greater than the last prototype showing the benefit of the slimmed stock. However the longer handle was an ergonomic nightmare for such work. No problems with excessive blunting with the secondary edge bevel. A slight steeling or couple of passes on the ceramic rod were all that was needed to restore the edge to razor sharpness.
The tension bar knife was used to whittle some wood for kindling. Two cups of shavings were produced with no significant effect on the edge. The knife could still pop dandelions for example. Some scrapings were also produced, again no visible blunting. The edge was restored with a few passes on a ceramic rod. The knife was used to chop down some Alders. The chopping ability was many times to one greater than the previous tension bar knife due to a combination of thinner blade stock and much more blade heavy balance due to the extended grip. The knife could easily lop off 0.5" thick branches and cut through 1.5" thick pieces in under a dozen hits.
The knife was tried out on a couple of other woods with no problems, fresh green soft woods. It could chop down 1-2" sticks with no problems, and easily handle the branches. However when it was later tried on some seasoned scrap (2x2), while the power was enough, the edge folded immediately on contact with the sharp corner. Of course there are no sharp corners on natural woods, but there are knots were are harder still to cut. The edge on the tension bar knife folded deeply on contact with the corner of the 2x2, taking a dent which was 0.020" thick at back.
On the undamaged section of edge, the knife was used to split some board which it handled easily. However during an attempt to split a 2x4 (one small knot), the blade just bent down readily under the impact of the baton, not even sinking to its width in the 2x4. Due to the much reduced stock thickness of this blade compared to the last one, it is *massively* weaker. It can be bend just by holding one part of the blade in the left hand, and pinching another between the thumb and index finger which is twisted to kink the knife.
With the much thinner blade stock the cutting ability of the second knife was evident on binding materials. The thinner edge also made itself felt on ropes, having almost double the slicing ability of the first prototype. However the edge was so weak it collapsed readily. With the higher cutting ability and heavier weight and more blade balance this version of the knife was a much more powerful chopper, easily able to handle wood of the size that frustrated the first knife. However due to so much steel being removed it lost the ability to handle some of the harder work.
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| Updated : | Jul 10 : 2006 |
| Originally written : | Jul 14 : 2003 |