The following knives were used to cut a variety of materials and their performance recorded :
|Spyderco Bill Moran||VG-10||60-62||8.5||2.7||0.085||20|
|Mel Sorg utility Hunter||D2||62||10.0||2.3||0.060||17|
|Phil Wilson utility Hunter||CPM-10V||62.5||10.0||2.4||0.025||15|
|Spyderco Calypso Jr.||AUS-8||58-59||6.2||2.7||0.055||20|
The blade stock was 1/8" thick for all knives except for the Mel Sorg utility hunter which was ground from 3/32" .
The sharpness of the blades was measured by slicing through a roll of heavy fabric and averaging the performance of three cuts. This was with the done after each of the four rounds of stock cutting.
The materials being cut were used and were lightly cleaned of dust and debris before the cutting. The rope was cut by pulling through a loop, push cuts were used through wood and cardboard. The wear was concentrated on one portion of the blade just in front of the handle. The fabric was sliced using the full length of the knife.
The following table shows the extend of blunting as indicated by the performance on the fabric after each round :
|Steel||Round 1||Round 2||Round 3||Round 4|
Due to some shortsightedness, the rolls of fabric used to test the sharpness were not the same size in every round, and thus the rate of edge wear needs to be examined from how the performance of the blades changes relative to each other.
In short; the AUS-8A blade falls behind the others significantly after round one, the VG-10 blade is also clearly behind but to a lesser extend, and it takes the full four rounds before the D2 blade can no longer stay with the CPM-10V blade. The AUS-8a blade simply could not cut the fabric after round four.
UPDATE : note how the rate of blunting isn't linear, the blades don't lose their sharpness at a constant rate. For example the D2 knife is very close to the CPM-10V one on rounds one through three, but suddenly in round four it is taking three times as much blade length, showing a large drop in relative sharpness. As as been shown in detail in more detailed recent comparisons blunting is strongly nonlinear [ref].
As the blades started to wear in the later rounds and the blade length required for the fabric cutting grew, a few simple tests of sharpness were also performed to see how readily the blunting could be detected with less numerical means. The blades were checked to see how well they could shave and slice a sheet of paper. The results :
|Steel||Round 3||Round 4|
|Shaving||Paper slicing||Shaving||Paper slicing|
This table clearly shows very clearly the distinction between the knives, and in retrospect would have been valuable to do from the start. While there is a lot of judgement used in such tests, they are quick and easy checks to do and give solid information about sharpness.
The extent of the blunting could also be determined in a very qualitative way by noting the behavior of the knives during the cutting. As the edges started to roll and wear, the push cuts degenerated into slices as the blades slipped along the material. The aus-8a knife exhibited this trend quickly while the VG-10 blade held up well until the third round. The D2 blade showed little loss of aggression the fourth round, where more of a slice was needed. The CPM-10V blade showed no detectable loss of aggression throughout.
UPDATE : this was one of the earlier edge retention comparisons performed, back in 1999. It has a few problems mainly the consistency of the force applied during the fabric cutting. As well the initial performance of the knives should have been recorded to insure that all were at the same level of sharpness from the start. Further the sharpness checks should have been confined to the same section of blade used to do the stock cutting. As well details on the grit finish used would have been informative.
The knives were sharpened as a further check for blade wear and overall extent of blunting :
Because the AUS-8A blade is that soft it can be readily filed, it sharpens very quickly with a butcher steel which acts as a fine file and allows it to be restored faster than the VG-10 knife. However it is still slower to restore than D2 and CPM-10V blade.
In summary, there is a clear performance difference in the steels tested in regards to edge retention on soft materials. The performance was as expected with D2 only being second to CPM-10V which was seemingly unaffected by the cutting even though it had the thinnest edge and smallest included angle in its bevel. It should be noted though that of course you have to pay for this performance increase. VG-10 stock is more expensive than aus-8a and it is harder to work .
You can comment on this write-up by dropping me an email : cliffstamp[REMOVE]@cutleryscience.com or by posting in the following thread on Bladeforums :
|Last updated :||Wed May 7 13:46:49 NDT 2003|
|Wed Aug 18 10:33:38 NDT 1999|