A custom folder by Roger Dole in CPM-15V

Introduction

Eli McBee had Roger Dole grind him a couple of blades out of CPM-15V. He had a few problems with sharpening and offered to have it inspected and evaluated.

Rough work

The edge was ground to an 11 degree bevel about 0.012" wide on a coarse Japanese Waterstone then then polished with an 800 waterstone and finished with a microbevel on a worn 800 grit ceramic rod at 20 degrees per side. The edge shaved smoothly.

First the edge holding performance was compared on 3/8" hemp rope to a Buck/Strider folder in ATS-34 with a thinned out edge, a Stellite 6K knife from Gerber, and a custom D2 blade made by Mel Sorg. The sharpness was measured by the force required (in grams) to push cut through thread :

The CPM steel retains a slight advantage over the ATS-34, but it also starts out slightly sharper, this is user influence not steel limitations The custom D2 blade at 62 RC significantly outperforms the other three. The extent of blunting was also measured by their ability to push cut the same rope. The necessary force was measured in lbs :

The changes in performance are much smaller than on the thread, which you would expect as the blade geometry plays a significant part in a blades ability to push cut rope whereas only sharpness effects its ability to push cut through thread. The CPM-15V fails to significantly outperform the ATS-34 blade and all are outcut by the custom D2 knife.

UPDATE : there are several problems with the above method. All blades should initially be at the same sharpness, the hemp rope should be cut unsupported, not on a cutting board, as otherwise as the force required to make the cuts will influence the rate of blunting by increasing the grating force against the cutting board as the knife cuts through the rope. As well all work should be repeated at least three times for stability.

Extended testing

The D2 and CPM-15V blades were compared a few more times on more times on cardboard and 1/2" hemp rope and the D2 blade would readily hold a higher push cutting performance. With repeated comparisons of the ATS-34 and the CPM-15V the performance in push cutting was again similar.

A more extended comparison was made against another ATS-34 blade with a similar edge profile, a Sub-Sniper from Lynn Griffith. 1/8" ridged cardboard was used as cutting stock and the sharpness was measured by push cutting light thread :

Again the CPM-15V blade did not significantly outperform the ATS-34 in ability to hold push cutting sharpness. During the cutting the slicing sharpness was also checked by by measuring the length of edge required to slice 1/4" poly under a 700 g load. The results :

Now the CPM-15V significantly outslices the ATS-34 blade and keeps slicing at a much higher relative performance level which grows as more cardboard is cut. During the last 100 m of cardboard the ATS-34 sees a huge decrease in slicing performance while the 15V blade holds constant. The cutting was stopped simply due to lack of cardboard.

UPDATE : again here ideally his is repeated a few times to stabilize the performance and the blades should be at the same sharpness initially. However this behavior of seeing a difference in edge retention from push cutting to slicing sharpness has been confirmed in many later reviews such as comparisons of S30V vs VG-10 at the same hardness where the much higher wear resistance of S30V only is an advantage in slicing sharpness same as seen for 15V in the above : ref.

A shot of both blades :

The curved portion of the CPM blade was never used during the cutting and the fractional length in the above table refers to the straight part of the edge which differed only a few millimeters. The edge angles are to within a degree, and the intial finish is very close. Both were sharpened on SiC sandpaper and finished on CrO paper to shaving sharp.

After the work was done both blades were checked under magnification, 10x. Both edges had a couple of chips about 0.08 millimeter in depth and a multitude of smaller ones, well below visible and can't even be readily felt by my fingernail.

With just 25 strokes per side on a fine DMT and then 25 on an x-fine, the ATS-34 blade was shaving sharp and showed no imperfections under a scope (10X mag). Similar work on the CPM-15 blade also left it shaving sharp but a few of the larger chips had remained, but were significanty reduced in size.

Comments

Comments can be sent to : cliffstamp[REMOVE]@cutleryscience.com and seen in the following ARCHIVED thread :

• Some comments on CPM-15V : light use only