We had knife sharpening competition with some heavy hitters in the Keeping Sharp sub-forum of the Knife Forums. The idea behind this one started out for guided devices such as the Wicked Edge (WEPS) and the Edge Pro, but quickly turned into a friendly “Clash of the Titans” with several methods of sharpening represented - from freehand to Edge Pro to WEPS to belt sanders. The thread can be found here.
As the host and honorary judge of this competition, I supplied 7″ Maestro Wu Bombshell Steel Chef Knives to the participants, without knowing who got which knife. I knew there would be no clear winner, and my main goal was to make this a learning project. And learn I did. The knives were all amazingly sharp and well done.
I took microscope pictures of before and after the cutting tests – and it is from these pictures that this blog post is based to support my theories on Overhoning straight razors. I know these aren’t straight razors, but the similarities to what I saw on straights when I honed and on what I saw on these knives sharpened by others gave some quantitative support to my long lingering theories. Besides, the guys sharpening were no hacks, and approached their sharpening in a similar fashion to straight razor honers.
All pictures here were taken with a Veho 200x USB microscope. Original resolution size is 1mm high x 2.5mm wide.
Overhoning is a controversial topic amongst straight razor honers. Most people who know me know that I respectfully do not subscribe to the theory, which basically states that too many strokes on a hone will cause the edge to become a “foil edge”, which is too thin to support itself and folds over during the shave; and/or cause microchipping in the final, and most delicate stages of razor honing.
As far as foil edges on straight razors caused by overhoning, the thickness of the spine of the razor combined with the width of the blade determines the edge angle. Since we hone razors with the spine flat on the stones or strops, the geometry is predetermined. If the edge angle should be too low and the steel quality isn’t able to support such an angle, it will fold or break. This isn’t a direct consequence of overhoning, as in too many strokes. It’s clearly one of geometry. Increasing the angle by adding a layer of tape will reinforce the geometry, thus stopping the breakdown or foiling when honing.
Once geometry is accounted for, one can arguably hone past the point of ideal or what is considered “enough” – in other words, “overhone” in the sense that you took more passes on the hone than was necessary. However, this shouldn’t raise a burr (with single side passes as in straight razor honing) but will continue to reinforce the geometry that is there. In an example taken from knife sharpening, where a burr is often formed and is the indicator for “sharp” on one side, it clearly is honed passed the point of “ideal”, but there is no foiling of the edge once the burr has been removed (unless the angle is too acute). The same applies to razors. Once you get “there” you will only continue to reinforce that angle. Of course, the idea is to know when to stop, but that is another issue (I’m not addressing the spine wear issue here) :)
That brings us to the argument of microchipping as a result of overhoning. It has long been my belief that what really happens is that each successive level of refinement ultimately exposes ever deeper scratches left behind from earlier stages as it establishes it’s own scratches. In fact, it’s not that the edge actually chips, it’s that the edge is refined enough with smaller scratches around it to reveal the gap left by the deeper scratch!
Below is a perfect example – the vertical deeper scratches lead directly to a microchip in the polished edge.
However, microchipping at the finishing stages is a real phenominon, as anyone who has honed a razor has probably seen the semi-circular chip-out just left of center, below:
This micro chip, and the triangular one to the right are often attributed to overhoning because these chips only appear at the final stages of honing. While I said before that the microchipping were preexisting gaps that become exposed, it could also be that because the scratches are so relatively deep, by the time the razor is honed to such a thin and even plane at the edge, a preexisting deeper scratch causes the chipout due to lack of support from the steel around it – a weak link, if you will.
Let’s take a closer look at that microchip and how it most likely formed:
If you follow the chip upwards from the edge, a deeper scratch is revealed in the bevel, as marked by the arrows. In other words, the deepest scratches from a coarser stone/belt/diamond plate had not yet been completely removed and only when the edge becomes thin enough so one can shave with it does the earlier damage become apparent.
At this point, an argument for the theory of underhoning – not overhoning – can be made.
Something to think about :)
In Part 2 I will discuss my theories on overhoning in regards to edges that are deemed “too refined”.