Thread: Convexed bevel, Good thing?

“Seriously, though. Thank you. It's interesting how everything ties together.”


Realize that none of us are using the exact same stones, prepared in the exact same manner, and honing the exact same blade in the same condition with the same level of experience and technique. Talk about variables.

It is not surprising that results are not predictable, or technique uniformly agreed to. There is also myth and questionable information in razor honing, that has influenced honing instruction for years.

It was not that long ago, mid 90’s when on this fora and others, the ultimate razor edges were said to have come off a Coticule or 8k Norton hone and even then synthetics derided as tools for the unwashed, by some. Any disagreement soundly denounced, lapping film… heresy.

We have come a long way. The bottom line is, there are a host of variables that affect edge creation and performance.

Additionally the somewhat recent availability and use of affordable high magnification, to see firsthand, the results of technique and stone/grit performance, have allowed the user to make more educated honing, progression decisions and develop edges well past the 90’s standards in both level of sharpness and comfort.

Sharp is easy, Keen, and comfortable, a completely different challenge.

I am not sure it is a myth exactly, but I think it could easily be an oversimplification. As you may remember, I was looking into blade design/manufacturing to try to make sense of some of the honing information. I talked to a custom blade manufacturer and he said that he designs his razors to be honed with one layer of tape. When I asked about the hone and edge wearing over time to keep a constant bevel angle he said he doesn't think that the spine and edge wear evenly enough for that to work.

And my head just started going through all the variables one would have to consider, and all the factors someone would have to control, in order to ensure that were to happen. But my rudimentary brain came up with about five before the words "oh my" escaped my lips.

Originally Posted by Euclid440

Micrographs of a convex edge.

Here is an interesting video by Dave Weaver, Dave is an SRP member but has not posted in a while. This video is part of a series on the “Unicorn edge” and buffing an edge with a buffer, posted on the Sawmill Creek forum,

While this technique will not work on a razor, it is interesting what his micrographs show of the edge taken of chisels at a side profile.
Actually I once used a buffer to smooth up a razor i could not get a comfortable shave off no matter what I did to it on a stone or strop. The trick was to not actually touch the razor to the buffer but rather let the outer fibres of the swansdown buff do the job. Physically could not feel or hear contact with the buff & I did it at 90º, just one pass each side Worked great but never successfully repeated the experiment so took the one win and folded

As Dave says, the technique is not new, I was first taught it by famed carver W.P. Wilcox in the early 80’s for sharpening carving chisels. W.P could not be bothered with sharpening on stones, except to remove chips and often said. “We don’t get paid to sharpen tools; we get paid to cut wood.”

And off a leather wheeled buffer they cut wood like butter.

What is new is Dave’s new look at the technique and experimentation with edge sharpness, longevity, and dramatic micrographs of the bevel side profile.

So, how does it apply to razors? Buffing and the result of buffing is exactly what we do by stropping. The strop works exactly the same way, except that it removes microns or fraction of microns, rather than thousands by buffing.

It has long been contended that stropping convexes a bevel or if done incorrectly rounds an edge. My contention has always been that convexing a bevel is a good thing and makes a stronger edge.

The best example is a Scandi grind vs a bevel grind on a knife. A Scandi grind is a convexed bevel on steroids. No question that a Scandi is a stronger edge than a bevel edge, and possibly sharper, or at least subject to less resistance. Think boat hull design. Yes, for delicate woodwork or slicing salmon but Scandis for bushcraft are often given a slight microbevel for strength also, even if just using a strop..

Dave also touches on how a buffed convex edge is stronger and cuts cleaner than a Micro bevel. And the video also makes an argument that bevel angle is not as critical as once thought, that bevel shape may trump bevel angle, Dave’s convex bevels are much steeper than the honed bevel angle yet perform much better.

So, yes Dave’s cutting wood and we are cutting hair, two different kettles of fish… or are they?

What are your thoughts?

Originally Posted by outback

I also understand that Samurai swords were honed in this fashion.

We also know that a Arch is stronger than a triangle,especially in stone bridges, and doorways

Yep except the whole sword, below the ridge line ( shinogi) is convex aiding in separation of the cut. How much depends on whether you want to cut bare flesh & leather armour or bust thru hard bamboo or metal armour.
Historically Japanese sword changed a lot to suit the armour of who they were at war with but I digress...

Good thread
One thing no one's mentioned is that western chisels like Jp kitchen knives & wakamisori are single bevel tools. The nature of the beast is SHARP convexed or not. On single bevel Jp knives & chisels you get the best of both world's with sharpness & cleavage & there is always a convex on one bevel. On wakamisori not the case with convexing. I don't think you can make a western chisel sharper thru convexing on a buffer but the more metal you create behind an edge always adds strength & the buff will give a smooth edge for sure..

Definitely slurry aids in convexity & that's one of the reasons softer jnats are preferred for polishing the bevel on Jp kitchen knives. Tool stones are a touch harder. Possibly plane & chlsel bevels are a bit less steep than knives & wakamisori stones are generally the hardest to actually prevent convexing the bevels.

Another reason that buffing will not work on razors is the compound. Polishing compounds are aggressive, usually Aluminum Oxide. They cut fast and polish well, but that same aggressive grit leaves a ragged edge on a micron thick edge.

Metal polish is a good example. You can easily and quickly polish a bevel with any good metal polish and remove all the visible stria (at about 400X power), by stropping on metal polish on a piece of pasted cardboard. But the edge will not shave comfortably, it is sharp, but uncomfortable. That same pasted edge on a knife, chisel of plane blade will cut wood like butter.

Add to that the abrasiveness of the cotton wheel alone and the fact that cotton wheels are not uniform in surface and you multiply the cutting ability and randomness of the cutting surface, the pasted individual cotton fibers. Now add speed and heat…