Edge testing on VG-10, D2, and CPM-10V

Material and geometry specifications

Details on the knives used :

As the Fällkniven knives S1 and WM have full convex grinds there is no distinct secondary edge bevels. However through the width of the edge bevel on the F1, the S1 and WM are thinner, and thus have a more acutely formed edge. The blades are all of similar widths, around 2.5 cm, give or take a mm or two.

Method

All blades were used and were fully sharpened before starting, finishing with a micro bevel produced from a 800 grit ceramic rod. The finish was decently consistent across all the blades, with the F1 and Phil Wilson hunter standing out slightly. The sharpness and cutting ability was determined by press cuts through six different grades of rubber tubing (1/4",2 pieces of 3/8",1/2",5/8",1") three times each, slicing through two different types of fabric; stiff synthetic and loose cotton, and finally slicing paper.

Cutting through the fabric was quite easy for all the blades. They were all very sharp and bit into the material well and cut quickly through the fabric. Unfortunately there wasn't enough cotton on hand to make a decent sized roll so every knife went through in one stroke though some required much less than others. The CPM-10V blade in particular needed little blade length to make this cut. The only problem with this cutting noted was the the choil on the Fällkniven blades would catch on the fabric which forces a less fluid pace.

The blades were then used for a variety of work to examine how they blunted. First fifty cuts were made though fifteen cm long doubled card stock, then fifty similar length slices were made into pine, then ten press cuts through RS-232 cable, and finally ten press cuts into the wire off of a table lamp. The cable and wire were cut resting on a 2x4" . A one inch section was marked on all blades and the cuts were focused in this area. The knives were then used to slice paper (compared against a freshly sharpened Spyderco Calypso Jr.), all had lost some ability except for the CPM-10V light utility hunter. The rubber and fabric cutting was then repeated as a further check on degradation. Details :

In short, the CPM-10V blade is clearly ahead of the D2 blade which stands out significantly in front of the VG-10 blades which all act very similar, except for the WM which is hampered by its much shorter blade length. Details on the rubber cutting was not included in the above table as the blades could cut it the same before as after. That cutting was more dependent on edge geometry rather than sharpness.

Some details on the performance during the cutting

On the rubber the cutting performance was dominated by geometry and went from Phil Wilson custom, Spyderco Bill Moran Featherweight, the S1 and WM and finally F1. The handle designs were also of consequence. The grips on the WM and Spyderco Bill Moran Featherweight are difficult to use under a lot of force as the handles are thin in cross section at the top and bottom which makes for a lot of pressure on the thumb and forefinger and underneath the pinky finger which forced constant breaks to prevent skin irritation.

All blades except the F1 and WM cut the card stock easily. The WM was hampered by its short blade length, no slicing motion could be used, and the F1 actually showed edge degradation and frayed the last few cuts of the paper. This carried over to the wood where the F1 skipped about 25% of the time. The edge did not bite in and make smooth cuts. All other blades easily went through the soft pine. However from previous work with the F1, S1 and WM, even at optimal sharpness, the v-ground bevel on the F1 is not as smooth on woods and such as the thinner convex bevels on the S1 and WM.

The RS-232 cable was easily cut by all knives. However the thicker lamp wire was more difficult and the 2x4" would indent visibly. The Spyderco Bill Moran and WM were again hard to use with the handle shape not being well suited to heavy forces. All the other blades cut the lamp wire well with the thinner blades needing less effort. In terms of edge damage, the F1 was started to show light reflecting from the edge and was indented enough so detect by fingernail.

UPDATE : the quick degradation of the F1 as compared to the S1 and WM was simply due to a poor initial sharpening which left some edge burr. The F1 was compared to the other blades in subsequent trials and fared much better [ref].

Restoring the edge

Each knife was honed back to optimal sharpness. The CPM-10V blade simply required three strokes on the butchers steel and three strokes on the ceramic rod. The D2 required five passes on the steel and fifteen on the rod. The Spyderco Bill Moran was steeled fifteen times and was finished with twenty strokes on a ceramic rod. The Fällkniven knives were soft enough to be actually filed by the butchers steel and with just ten to fifteen 15 strokes they all had an aggressive finish that would scrape shave a little and nicely slice paper.

A side issue - coarse vs polished edges

As the edge on the Fallkniven blades was restored so well on the butchers steel, this edge was investigated for a few types of cutting to see how it compared with a finer polished edge. First off was some wood cutting, 500 chops, with the sharpness measured before and after by slices through a roll of car mat, with the number of blade passes needed as a determination of sharpness. In short, the edge showed rapid degradation, the details :

The work was then going to be repeated with the fine ceramic finish, however that edge degraded too quickly during the car mat cutting which served as additional blunting stock and thus wasn't a decent measure of sharpness. The higher polished edge took eight to nine full slices to cut through the first three sections of mat and then took more than fourteen on the last two. This was repeated a few times with both finishes and the behavior was consistent, the rougher edge lasted much longer during the abrasive slicing. Some details :

A comparison of coarse vs polished edges in wood chopping was also performed with the Busse Basic . In that work the fabric used to determine the sharpness was not very abrasive and thus wasn't a significant factor in the blunting process. In short, the more coarse edges degraded significantly faster in chopping [ref]. Similar work comparing coarse vs polished edges slicing has been repeated many times showing the much greater cutting ability and edge retention of coarse edges : ref.

Modifications to the method

As a better test of durability, the harder materials like wire should be cut by making a loop and then pulling the blade through. When the blades are simply pushed through all that is being tested is the hardness. Pulling the blades through the wire produces an initial violent impact followed by sudden shear forces, both factors have the possibility of inducing chips thus this could be used to estimate edge toughness.

UPDATE : this was one of the earlier comparisons performed back in 1999. Many of the techniques for determining sharpness and edge retention were just being developed. Current techniques are much more robust and eliminate problems in the above such as controlling the consistency of tension in the fabric during the cutting [ref].

Comments

Comments can be sent to : cliffstamp[REMOVE]@cutleryscience.com . Feedback can be seen in the following archived thread on Bladeforums :

• Edge testing : VG-10 (Spyderco / Fällkniven), D2, and CPM-10V