Alternative testing medium (for cutting)

[matthew rapaport]

I notice that sometimes knife testers (particularly Cliff Stamp) look for particularly tough media that dull knives fairly quickly, but do their dulling as the direct result of cutting though something (as distinct from say dragging the edge through sand, digging, or sawing concrete). The other day I had to cut up a cardboard carpet tube, and I realized that this media is a good test of knives on a number of levels.

Carpet tube is hollow, about 14 inches in diameter, and a full .25 inches thick! It is incredibly tough to cut through. If you cut more than 5 or six inches from the edge of the tube, the cylindrical shape causes the cut cardboard to push back against the knife binding it heavily. If you cut an inch or two from the edge, this effect is greatly reduced and you end up with a purer cutting (edge) test, not to mention an easier cutting job all around.

More important than individual results were their general characteristics. The knives dulled quickly. I tested about a half dozen fixed blades in the 3-5 inch (blade) length range. All of these particular knives had be taken to a hair-popping semi-smooth edge by a DMT alignment jig set to about 20deg. (40 deg. included). Some of the knives (like my Dozier K1) are the sorts that people note will cut 250+ pieces of 1" hemp and still shave. I can tell you that mine didn't shave any more after about 2 linear feet of this cardboard tube! This is a great medium for dulling a knife quickly, while really cutting something.

As much as an edge test, the tube was also a great handle test! This process requires considerable effort, especially downward pressure if you want to see what the knife feels like when it binds up. I didn't even try this with wet or slippery handles, but I could see that without a guard or some other method for keeping the hand from sliding up onto the blade, this medium could be dangerous! Besides this, any problems in the match between handle and the tester's hand will show up quickly.

I tried chopping it too, with 3 different machetes (Livesay RCM, Aki SBM, and a 15" barteaux). If you don't hold the tube down, it just bounces away from a chop. Held still, the cardboard still had a tendency to deform before it cut, but either way, the heavier Barteaux and RCM machetes could, at least, slice into it. The ultra-light SBM just bounced off.

 

[shortgoth]

Whaty you say is very true, I test all my knive's edge holding, sharpness, and handling/feeling with various thicknesses of cardboard and paperback books (great for penetration tests), old t-shirts, and jeans. It allows me to test with what I personally am most likely to be cutting up.

I don't know about you guys, but testing a knife with metal, thick hardwoods, and concrete seem pointless. I have better tools than a knife for these purposes.

I also test cut on my own skin because there's no reliable substitute to discover how well it cuts flesh (although I only do small, shallow cuts). I tried many different mediums (PVC and rubber are quite comparable), but this way you get a much beter "feel" for the how the blade acts rather than just looking at test cuts.

But I'm insane *g*.

Danny

 

[Cliff Stamp]

matthew rapaport :

... do their dulling as the direct result of cutting though something (as distinct from say dragging the edge through sand, digging, or sawing concrete)

The reason that I cut material to induce blunting is that at the same time that I am getting information about edge retention, I am getting information on the cutting ability. There is also the added benefit of having the numbers be more meaningful. If I say it takes XX passes through sand before some level of blunting, this is not as readily understood as YY cuts through rope.

... cardboard carpet tube, and I realized that this media is a good test of knives on a number of levels.

I used to use heavy cardboard and it is an excellent testing medium for the reasons you mentioned. The only reason I don't use it a lot now is that I don't have a lot of it on hand. I switched to hemp rope as the primary medium I use for edge retention mainly because it is popular. I have been looking for a readily available high abrasion medium, like fiberglass insulation but easier to handle.

-Cliff