Edge retention push cutting pine - Spyderco Fine finish


Introduction

This work started for one purpose but evolved into another. The initial reason was to look at the edge retention with repeated use of the Spyderco Fine rods without resetting the edge to remove fatigued metal. The goal there was to see if the rods could abrade the damaged steel and set the apex on undamaged steel.

A second point of comparison was added with multiple knives were used to look at the general edge retention of various steels. Now to be clear, the knives did not all have the same geometry, even the same apex bevel angle which itself will significantly influence edge retention 1 and so this comparison was intended to be purely qualitative.

Method

The method was fairly simple for all knives :

Thus there were three edge retention cutting runs. The first question was to see if the edge retention would consistently degrade from the first run to the second and even more on the third. This would be due to weakened metal from the apex not being removed and building up.

This entire process was repeated multiple times with multiple steels to check for consistency as well as if there was a pattern from one steel to the next.

Results

The full results :

K2/Farid 10V/60+ HRC : 0.020"/9-10 dps/15 dps apex bevel

-Initial edge : 350 (25)
-Apex reset : 300 (50)
-Second apex reset : 350 (25)

Pingo N690Co: 0.010"/>15 dps/20 dps apex bevel

-Initial edge : 400 (150)
-Apex reset : 450 (25)
-Second apex reset : 750 (75)

Jeremy McCullen SM-100 : full grind / 6 dps edge / 15 dps apex bevel

-Initial edge : 450 (75)
-Apex reset : 400 (50)
-Second apex reset : 300 (50)

Svord 350B 15N20 0.012/12-13 dps / 15 dps apex bevel

-Initial edge : 750 (25)
-Apex reset : 400 (50)
-Second apex reset : 250 (25)

Chigago 440C : 0.015"/13/14 dps/15 dps apex bevel

-Initial edge : 850 (25)
-Apex reset : 800 (50)
-Second apex reset : 550 (25)

Hunter (Big Chris) 10V-64 HRC : 0.012"/13-14 dps

-Initial edge : 1000 (50)
-Apex reset : 850 (50)
-Second apex reset : 650 (75)

Schrade SCH104L 9Cr18 : 0.028"/16-17 dps/20 dps apex bevel

-Initial : 1100 (100)
-Apex reset : 750 (25)
-Second apex reset : 850 (75)

Vagabond AUS-6 : 0.021"/12-13 dps / apex bevel ~15 dps

-Initial edge : 1350 (50)
-Apex reset : 700 (200)
-Second apex reset : 300 (50) 

A condensed list, just showing the rank from least to highest :

Discussion

The first immediate point is that there was no correlation between the type of steel and the edge retention results. While this may at first seem to be surprising, all it shows is that there is a large random influence to the results from the wood. While this wood was all the same time (scrap pine) from the same type of lumber (trim wastage). There was enough of a difference in the wood to be larger than the difference in the steel. This should give pause for thought in general about comments made about edge retention even when the material is thought to be fairly consistent. Of course the difference in wood could be dealt with by random sampling the pine.

The next point is more interesting. Note that with some of the knives like the Vagabond there is a large difference between the initial edge retention and the second and third. As just the apex was reset the edge retention dropped off rapidly. First to 50% and then to 20%. However some knives were able to maintain edge retention without any significant drop off, the Pingo for example. What is the explanation? There was a change in how they were sharpened.

After the first few blades it was reasoned that the reason that the edge retention was suffering was that the apex was being deformed significantly vs being abraded due to the pressure being above what was necessary for abrasion. To test this idea the force was reduced steadily until it was taking 100-150 pps to apex the blades. With this very low force (barely making contact, 5-10 grams) then the edge retention could be maintained consistently. However from a practical perspective this isn't efficient. A more sensible method would be to use a more abrasive rod to remove some of the fatigued steel and then apex on the Spyderco Fine.

Recap

For more details/discussion see the following forum threads :

References

1 : Micro-bevel influnece on edge retention slicing hemp (VG-10 and S30V)


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Written: 17/01/2015 Updated: Copyright (c) 2015 : Cliff Stamp