a model for edge retention and the results of cardboard cutting on four S30V blades

[dante]

The opening hole does remove a lot of strength, that is where it broke and it is ground through the thickest part of the blade so the knife essentially has the functional stock just below the hole. It wasn't really a test as just as much as a spurr of the moment thing. It isn't a functional issue with that blade.

-Cliff

Cliff,

On your experience, do you think that the Spydercos and Striders SMF, SnGs etc... are compromised because of the hole? (I'm sure it does debilitate de blade overall) where does it looses it the most is it during (A) twisting, (B) batoning and/or (C) chopping? I was about to ask in the Strider forum this question regarding which blade was stronger, the AR or the SMF but I was afraid to be accused of "heresy". Based on your testing of the Manix looks like Spyderco has reinforced the design so it does not become an issue, but I'm curious of your observations on this.

 

[Cliff Stamp]

Is this number correct?

Nope, bugger. I was using bc scripts to do some calculations and had the power set at 0.5 when I calculated that.

It looks to be more like 55% more material.

Nice eye, the equation coefficients give 57 (8)%. This number is just the edge retention coefficient ratio raised to the power inverted [1.36^(1/0.685)].

On your experience, do you think that the Spydercos and Striders SMF, SnGs etc... are compromised because of the hole?

If you chop out a section of the blade it does make it weaker. However on most models and in most uses it doesn't induce a functional weak point, it will still break somewhere else first. Recently using a Pacific Salt for twisting and prying, the pivot loosened far before the blade was stressed significantly.

On most of the knives the tip is also fairly weak due to the tapers and efficient cutting grinds Spyderco uses so the tip will just crack off before there is any danger of loading the blade through the hole. This of course is the classic tradeoff of cutting ability vs utility strength.

Note that the hump Spyderco uses compsensates for the loss of material for the hole. Thus there is less of an overall weak point than what would be induced with a much more narrow blade and an oval hole. If you trace a line back and convert Spyderco blades to more traditional shapes you will see you actually remove most of the hole.

I was about to ask in the Strider forum this question regarding which blade was stronger, the AR or the SMF but I was afraid to be accused of "heresy".

Generally hype isn't very responsive to critical analysis.

-Cliff

 

[kel_aa]

Nope, bugger. I was using bc scripts to do some calculations and had the power set at 0.5 when I calculated that. ... the equation coefficients give 57 (8)%. This number is just the edge retention coefficient ratio raised to the power inverted [1.36^(1/0.685)].

Darn, I was hoping you would say I typoed 85% instead of 55%. Then I would have said don't you wish you were less hard on McClung?

 

[Cliff Stamp]

I have made my fair share of typing mistakes, the reviews are full of them. Some are trivial, some are fairly serious such as now/not which can change the meaning of a sentance. McClung gets a few jibes for the "I was a professional soldier for 2/5 years." mainly because he is so demanding of Strider in spite of his own less than definate history. This is like McDonalds critizing Burger King for the lack of nutritional value of their food. You can't even take the arguement seriously.

-Cliff

 

[Don M]

The 57% is much more in line with what I have seen of CATRA numbers (posted on the forums here recently). This is actually more of a difference between S30V and ZDP-189 than the CATRA results would indicate. But they are for a different type of test using a different medium.

 

[Cliff Stamp]

Spyderco reports 565 vs 750 for CATRA so 33 %. This according to descriptions is the number of cuts to reach a specific state of blunting so it would corrospond to the 57 (8)% obtained in the above. These can't be compared in a meaningful way as there is no quality determination on the CATRA results, meaning no way to bound the expected performance. This comes from duplication on different samples to see how much the edge retention changes from one piece of steel to the next as well as just variation in the actual cutting, media, and initial sharpening.

It is possibly, though unlikely for example that the Military I had represents the "average" Spyderco blade more so than the Para/Manix. Using this blade vs the ZDP-189 would give a number very close to the CATRA results. Note what would happen in the extremes of comparing the Rat Trap to Calpyso Jr. or the Military vs the Delica. This is one of the problems when working with small samples and why it gets much more informative when you have a larger sample size.

As noted though you would never expect the number to be exact as they would depend on the edge finish, angle and even media. This is why to be comprehensive you could test on say hemp, cardboard and carpet with multiple knives for each and then in the end present an average increase in slicing aggression overall that media. Similar would have to be done then for push cutting.

As always, the above isn't done to represent a "final word" on the subject but mainly to outline how such work can be done and offer essentially one data point. This has to then be integrated into all other unbiased/non-shill information to obtain essentially the population behavior. I will be repeating this on carpet shortly hopefully if I can obtain some as that is much easier to work with as it is insanely abrasive and thus the runs are almost immediate.

I should do the push cutting work as well, but that is very tedious to measure. I should just buy a force probe as that makes it trivial and extremely fast and precise.

-Cliff