As received edge retention slicing half inch hemp

Introduction

This experiment in determining the edge retention of knives as-arrived would have been a lot more fruitful had it been done when I had started collecting knife. The amount of data thus ammassed over the years would have been interesting. But still, even with a reduced data set, there are still some points of interest in the results.

To be clear, as the edge retention is determined as-arrived by slicing half inch hemp only one run is performed (as I can't replicate the as-arrived edge). Note that many properties effect edge retention such as :

and so care has to be taken in interpeting the results. In particular the data can not be used to infer anything specifically about steels except in the most broad sense. The main point is to look for large patterns. Does a particular maker/manufacturer in general perform higher/lower than another? Does a particular steel in general perform higher/lower than another. But again, due to the large number of influences it is likely to take a very large data pool to show anything but random scatter.

Method

The half inch manilla hemp was cut using a draw over two inches of the blade, there was no support under the rope, it was cut extended over a piece of wood so the blunting was from the cord only. The edge retention statistic used in the comparison was the TCE or total cutting efficiency which is calculated very simply as the sum of :

This statistic is easy to calculate and is a pseudo-integration and thus is fairly stable over multiple runs. As always, there has to be some stopping point set, and here it was 1.5% of optimal. As only one run was done there is no way to put confidence intervals (error bars) on the data.

Results

edge Retention as received
As received edge retention

Legend

Knives used to date :

Discussion

At this point there isn't enough data to draw any conclusions aside from the obvious that as-factory edge retention scatters widely. This pattern of heavy scatter is also seen in the comparisons done by Global on factor sharpened vs hand sharpened edges on many brands of kitchen knives. 1. The interesting question rasied there is how much of the increase in CATRA result was obtained by increasing the quality of the edge vs the grit change vs the angle change as all are significant factors in edge retention 2, 3.

What can be said? It looks like that a general rule could be nothing more than whoever sharpens the knife with the lowest angle (within reason) with the most coarse edge, and does the best job on sharpening - has the best performance. It doesn't look like steel has nearly a strong an influence given how widely the results scatter around the steel. This might be an odd result given the emphasis put on steel - but in a practical sense it makes a point.

Recap

For more details/discussion see the following forum threads :

References

1 : Global CATRA test on factory vs hand sharpened edges

2 : Influence of apex grit finish on edge retention slicing hemp with 3Cr13 stainless

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