Hamaguri edge and Flat bevel

[Brian Holcombe]

I wanted to detail a hamaguri bevel and flat bevel for interest of discussion;

Flat bevel (without micro bevel)



Zero distortion in the reflection



Hamaguri (curved) on the left




Hamaguri on the left again




I thought I would take a moment to detail these since they were discussed in the freehand thread. Basically the only way to make a hamaguri edge is in fact freehand, however it's not always wanted. Only in certain circumstances would you want one, really anywhere where you need something super strong but not necessarily as sharp.

I've been chopping rock maple and so my bevel is a hamaguri, if I were working softwoods I'd probably reduce it or remove it to be more like the paring chisel.

[Derek Cohen]

Brian, I am curious about the need for a hamaguri bevel (and just so you know, this is the first time I have heard the name).

As you know, I work almost exclusively with hardwoods. Most of them are no doubt much harder than the rock maple you are using (with which I am familiar).

My slicks are by Kiyohisa (as you may recall), and these are only pushed. They have a 25 degree flat bevel, since I wish them to be traditional.

I only freehand chisels (mostly other blades as well), so when it comes to my Koyamaichi dovetail chisels I go down a non-traditional route. I hollow grind them, and do so almost to the edge of the bevel, using a Tormek (to keep any heat down). This method ensures really fast re-sharpening (as I hone on the hollow). These chisels get wacked into some seriously hard, abrasive and tough wood yet have never chipped or failed in any way that would make me question the method of preparation.

Now a hollow grind is the very opposite to a hamaguri bevel. Why do you think that this (extra) work is really needed?





Guess which is which.

Regards from Perth

Derek

[Christopher Charles]

Makes sense. Rock maple? Now I'm curious...new project?

C

[Brian Holcombe]

Chris....nah, same project just more of it, lol. I'm using maple for the drawer sides.

Derek, I won't say it's required by any means but a combination of a hamaguri bevel and a very hard cutting edge makes for a chisel that goes a great deal of time with just the plain strop between sharpenings. However, in my experience still makes a very clean cut.

Those Kiyohisa's are damned sexy and 25 degrees is very impressive, especially in the woods that you cut. It's a testimate to the quality of Kiyohisa.

Do you maintain your bevels in the traditional method on the Kiyohisas?

I have worked on Ipe with handtools, so I understand your pain, lol.

[david charlesworth]

Brian,

A simple sketch shows that, at the same sharpening angle, the flat bevel has more metal supporting the edge than the elegant convex curve.

I have never been able to fathom the purpose of the curve. (Except for levering with mortice chisels).

Help?....

David

[Brian Holcombe]

Do you feel it impossible that there is a practical advantage to the shape that may be easily overlooked? Is it possible that the extreme edge being at a high angle is better than having the full bevel at that angle in some aspects.

It's not proper to lever out with Japanese mortise chisels, they are made with a very big section of hard steel at their edges and so the extreme edge can chip if you lever with them. I've found this edge to be easier to chop with than a flat bevel at the same ultimate edge angle.

[ian maybury]

Definitely no claims to expertise or historical knowledge made here.

Judging by the ever eminent Mr. Google just now 'Hamaguri' (clam shell) seems just to be a general Japanese term that's applicable to all sorts of edges - including especially chefs knives, swords and who knows what. While there's not much mention of it in connection with chisels, the purpose seems basically as Brian suggests to be to deliver a thicker and more damage resistant edge. It also in the case of chef's knives allows a usefully flat/shallow/almost vertical bevel on the cutting side, but helps to separate away the cut piece of wet whatever to the other with minimal suction/stiction.

Judging by the many pages of minutiae coming up on the web it seems as in most of these things originating in the east there's a tendency for various western groups to get cultish, mysteryish and one uppity about them.

it seems likely though (??) that the reality is pretty straightforward - that it's the edge you end up with if you run into a problem with a single bevel edge ground at some existing angle chipping, and put a steeper microbevel on to strengthen it. Rounding over afterwards may deliver some benefit in certain situation (when chopping on chefs knives above?), or maybe it's mostly aesthetic?

Must say my way of looking at this sort of stuff (hollow bevels/flatbevels/microbevels) is that it's another practial technique to have available in the armoury - to bring out if problems arise. There's by definition no ideologically absolute right or wrong - in that a very good quality chisel may function perfectly well at a given angle with a hollow or a flat bevel, while one with poorer steel or heat treatment may in the same situation chip like mad and benefit from said micro bevel....

[Brian Holcombe]

I feel similarly to Ian, I'm not part of the cult, but I like and take alot of aspects of it, the Hamaguri edge partially being one of them;

This is after a full day of chopping dovetails;


Having used plenty of chisels and variety of edges at this point I think it's significant.

[Malcolm McLeod]

Brian,

A simple sketch shows that, at the same sharpening angle, the flat bevel has more metal supporting the edge than the elegant convex curve.

I have never been able to fathom the purpose of the curve. (Except for levering with mortice chisels).

Help?....

David

Pardon the intrusion, as I'm WAY out of my element here...

But I saw a special on one of the big-number TV channels about Japanese swords and this curved sharpening. The theory presented was that the blade presented less surface area in contact with the material being cut, and so less friction. Essentially 2 points of contact: one tangent contact of material on the curve wedges the already cut material out, allowing the second actual cutting edge to penetrate deeper.

[ken hatch]

Brian,

The bevel on the first chisel looks like it was finished on a natural stone, a beautiful bevel. It's a sick puppy that loves a beautiful bevel....., That or older than dirt.

ken

[Reinis Kanders]

Looks great!
Roughly how long does it take? Do you do this for special occasions?

[Brian Holcombe]

Ken, Oh, do I love a nice bevel Thanks for the kind words, both were actually finished on the same Nakayama asagi, but the hamaguri bevel will mute the contrast in some lights.

BTW, Have you noticed your Kikuhiromaru to show a damask pattern in the jigane? I found it in mine and I am assuming currently that it shows from a great deal of cold work?

Reinis, thank you! Doesn't take long, I make a flat bevel first then work it a bit more freehand when I want the bevel to become a hamaguri shape.

[Stanley Covington]

I have never heard the term hamaguri used for chisels, but only for swords and knives (and chonna, but the shape described is different than for sword or knife). It translates to clam, a good descriptive word for the curved bevel.

A curved bevel is very handy when the chisel needs to be used to make a scooped cut. Much easier to do than with a straight bevel. It is a common sharpening technique for carving chisels, therefore.

Geometrically, it clearly gives the thin metal at the cutting edge more support than a straight, flat bevel, but in deep cuts, it experiences increased friction. If you are chopping hard and fast, and keep the bevel oiled, this is not a bad thing because it tends to kick the waste out of the way with more force.

There is a tendency, even among skilled professionals, to unintentionally gradually abrade the bevel a bit shallower (lower) with each sharpening. When the angle gets too low, the edge starts to fail, and the craftsman then hand grinds a secondary, steeper bevel, and the curved bevel is created.

But there can be no denying that the curved bevel takes longer to sharpen, so except in the special cases mentioned earlier, most guys will make an effort to work the blade gradually back to a flat bevel.

A curved bevel makes no sense for a push chisel, except, as mentioned above, for carving or making scooped cuts.

All that said, there is nothing physically wrong with a curved bevel: They cut just as well as a flat bevel of the same degree of sharpness.

弐円

Stan

[Brian Holcombe]

Thank you Stanley, I appreciate your weighing in!

[Pat Barry]

This is what my bevels always seem to look like when I freehand hone them. I always thought it was undesired. Seems to me there is no benefit regarding freehand paring but for chopping with a mallet it does improve the edge support.

"BTW, Have you noticed your Kikuhiromaru to show a damask pattern in the jigane?" --- WTH does this mean? Way too out there for my understanding.