Opinions of Zero Ground Blades

[me2]

I recently got a CRKT Hissatsu and am impressed by the cutting ability for such a thick spine. I have seen some advertisements for a design by Wally Hayes that is zero ground from 1/4" stock. I understand the scandinavian ground blades are zero ground, or have a very small secondary bevel. What are the general opinions about grinds like this? The hissatsu seems ground at about 12 degrees per side and seems fairly durable. I used it to trim some brush out back, and it took a couple of hits into the dirt at the top of the bank. I have ground a couple of blades and was thinking of trying some like this.

 

[Cliff Stamp]

...a very small secondary bevel.

That is the best way to do it in general. The secondary edge bevel adds greatly to the edge durability, many times over, and even more to the ease of sharpening.

Take that blade and heavily dull it but cutting something decently abrasive, or worse, damage it by hitting something accidently like a staple. Now compare the time spent sharpening it with and without a secondary bevel, one is literally a hundred times slower.

Now for some knives you don't actually need any more durability and the edge can be as acute as you can go, knives used for soft materials only like woods, cardboard , ropes and foods. So now you want that really low angle but you don't want the horrible resharpenability.

The solution is to run a full hollow primary grind right to the spine which leaves the edge at ~0.005" thick and ~5 degrees per side. You now sharpen flat to the stone, but the only part which makes contact is the very edge bevel so ease of sharpening is very high.

As for the thick zero blades :

The reason that the blades cut well even though they have thick spines is because in general materials don't exert forces uniformly in magnitude along the blade, they fall off rapidly from the edge.

This means that the edge angle and thickness are very critical to cutting ability for a lot of materials, in fact for some they are all that matters. You can however see the effect of the thick spine on heavy binding media like 1/4" cardboard.

Even though your 1/4" spine chisel will go into this well, once the 1/4" spine is in the cardboard it will start to wedge heavily and a much thinner blade will out cut it, even if it has a more obtuse edge bevel, as now a significant fraction of the force which needs to be overcome is due to side wedging.

As a general rule, in order for the blade to actually effect the cutting ability the material has to be able to "see" it. This means the material has to come in contact with it an exert a significant force on it.

For example I have a 22" Ang Khola khukuri which is massive at the spine, 1/2"+, it however readily cuts brush effectively as the spine never gets near it, even on heavy chopping where the blade is sinking 2"+ into the wood, the spine is never in it.

The knife cuts well because the edge is ground well and the blade has a nice taper up from the edge and that is all that the material sees when it is being used to cut.


-Cliff

 

[JDBLADE]

Posted by Cliff Stamp
That is the best way to do it in general. The secondary edge bevel adds greatly to the edge durability, many times over, and even more to the ease of sharpening.

Whilst many meat workers like a blade virtually zero ground they always add a secondary edge. When they get a new knife they grind it down to Zero then add the secondary edge this means they are only sharpening the secondary edge until the blade becomes too thick then they grind it down to Zero again. If they have a skinner or steak knife they have plenty of "meat" (pun intended) to play around with but with a boning knife esp., the curved they have less to grind and this is why a boner might only last 5 or 6 weeks. The meat worker normally only steels his knives during the working week and then hits the stones on the weekend. With the low hardness of the common butchers knife and a steel that secondary edge will last a week.

 

[Cliff Stamp]

... grind it down to Zero then add the secondary edge

In "The axe book" the same proceedure is used on axes, grind the full bevel, usually 1"+ wide and then add a micro-bevel which is really obtuse, >20 degrees for durability. J.J. of Razor Edge, and Leonard Lee of "The complete guide to sharpening" also promote the use of secondary edge bevels and relief grinds.

I actually do the relief grinds on mine a lot, but I am really particular. In fact I never let the secondary edge bevel become visible at all, let alone thicken. However when I recut the primary grind I only use a x-coarse stone, since that isn't forming an edge it is just shaping and that is usually a matter of minutes.

The big problem without the secondary grind is actually sharpening the 1"+ bevel as now you have to finish work the entire thing, if you want a high polish on the edge you basically have to hand sand a blade every time you need to sharpen it, this is just painfully slow if the knife is any way seriously used, and if you damage the edge, which isn't hard as there is no additional bevel for security, then you better bring on the power tools.

James Mattis was a big promoter of using zero ground puukko style knives for heavy utility, and I mean serious use, but he didn't even advocate sharpening them, he just treated them as disposable blades.

-Cliff

 

[thombrogan]

The big problem without the secondary grind is actually sharpening the 1"+ bevel as now you have to finish work the entire thing, if you want a high polish on the edge you basically have to hand sand a blade every time you need to sharpen it, this is just painfully slow if the knife is any way seriously used, and if you damage the edge, which isn't hard as there is no additional bevel for security, then you better bring on the power tools.

Too true, but the beauty of having to do that with low-chrome steels is a lot of bright, low-temp sparks for people amused as easily as me.

I have a question regarding unpolished spine-to-edge relief grinds:

Assuming one desires a highly polished edge, how much work is needed to grind the furroughs dug by the coarse abrasive away from the edge?

 

[Sal Glesser]

Somewhere between a straight razor, which is zero gound and stropped to create an even thinner "burr" (no impact) and an axe for high impact, there are a large number of combinations for edge angle, relief angle and blade geometry.

The first question is "what are you going to cut?"

I agree with Cliff on the response of the materials to cutting. If you are going to "pass through" the material with the entire width of the blade, such as in thick cardboard, the "binding" effect is more than many imagine and must be taken into serious consideration.

If one is just using the edge, such as in skinning, then the relieve angle can and probably should be much thinner than the spine (deep hollow grind)because there is no "pass through".

"Impact needs" will shape the edge geometry and "pass through needs" will shape the blade grinds.

Ed Schempp has done much testing on the pass through geometry's and he says he keeps getting back to the Japanese sword "style" where the thickest part of the grind is not at the spine. This provides strength, but offers some relief because the spine is not the thckest part of the blade. He likes "hamaguri" (apple seed) grinds, as to most of the bladesmiths. I think this is because of the constant "relief" that occurs in the pass through.

I've been testing his "camp Knife" style and his "wood cutting" blade geometry's "in the field" and am finding there is much truth to his concepts. I burn firewood for heat, which I cut. Ed designed and built a special "wood cutting" geometry model - 10.5" blade. Works better than anything I've used to date.

This adds another variable; "where to put the thickest part of the grind?".

Some knife designers design their blade grinds with much thought to appearance, since most knife buyers purchase "by eye". Some go the other extreme. I'm told that both can be done, but IMO, there is always a leaning to one or the other.

When you design your blade, the function will ultimately determine the thickness of the spine.

Let us know what you end up with. Sounds like a fun project.

sal

 

[Cliff Stamp]

Assuming one desires a highly polished edge, how much work is needed to grind the furroughs dug by the coarse abrasive away from the edge?

If you run down abrasives in many steps, it is faster but it takes a lot of steps. Essentially you are putting a mirror finish on the blade, that takes forever with zero grinds unless you have power equipment. Try it with D2 or S30V if you have some free time.

Mel Sorg used to grind such blades out of D2, 62 HRC, full cryo, single bevel, edge to spine, his father used to use them as a paper cutter. He would sharpen the entire bevel, but put a slight roll on the end of the stroke.

This way you again create a small secondary edge bevel, you can't see it as distinct, but it is there and it again massively speeds up the sharpening process. A hollow relief grind like Alvin runs would be more optimal however for sharpening.

Large parangs are typically sharpened zero bevel, once a week and it takes a half an hour to a full hour to sharpen them. I actually run some large blades like that because I don't mind the sharpening time and the edge simply doesn't get that worn cutting woods. I usually don't go beyond a 1000 grit to start.

Does it ever suck when you slam it into something though. I wanged a large custom "parang" into a brush covered rock a few years back and there is still a visible dent in the edge near the tip, it would take me hours to remove it if I just kept polishing the flats. Forget that, it will come out with sharpening eventually.

...the thickest part of the grind is not at the spine

Most traditional wood cutting blades are like this, parangs, goloks, and splitting axes, anything designed to go all the way through the material. Felling axes are typically thicker near the top, but that part never sees the wood anyway.

You can easily argue the profile you describe from simple drag principles, a simple flowing shape will reduce binding by allowing gradual deformation of the material being cut rather than an abrupt transition from full thickness to nothing at the spine.

What you have to watch out for is that if you move the thicker part towards the middle you are shallowing your grind and thus making the profile more obtuse. For example a full flat ground 2" wide bowie with the 1/4" at the spine has a nice thin profile, put the 1/4" in the middle and now you have a half height sabre grind.

Daggers cut poorly for example for just this reason. Most wood cutting blades which are of this style compensate for this effect by lowing the maximum thickness, or running the edge thinner to get the cutting ability back up. Or like the larger smatchets, run a really wide blade so you can get decent height grinds.

-Cliff

 

[knifetester]

James Mattis was a big promoter of using zero ground puukko style knives for heavy utility, and I mean serious use, but he didn't even advocate sharpening them, he just treated them as disposable blades.

For those interested James Mattis was one of the founding members of the online knife community, he ran a web site called Chai (meaning life in hebrew) Cutlery. Known for it Karma points (10% of the order would go to a charity of your choice or from a list). He was a CPA by trade and his wife Toni was a lawyer, good people. Before the days of digital cameras, JKM used to have some of the best scans of knives.

As Cliff points out, JKM used to advocate the use of mora type knives, though fairly common today this was fairly unusual at the time.

Back on point, with very aggressive abbrasives (80-100 grit AO belts) you can remove metal really, really fast even without power. So as long as you are not looking for a fine wood carving polishe edge, you can reset a zero ground edge pretty fast after some minor chipping. The simpe carbon steels used in mora knives are ideal for this.

I keep some beater moras around for the use that JKM advocated, and they perform very well. For uses like cutting carpet into strips, then rolled up for disposal (very, very hard on an edge), cutting sod, deburring brass and aluminum, cutting hard plastics, etc, the mora knives do very well. The "zero" edge is very acute.

Yes, a secondary edge is faster to sharpen, you have *much* less metal to remove. So, for some applications it is better, for others (like wood carving) a high polished single edge bevel (i.e zero grind) is ideal.

IN the end, I think different geometries work better for different purposes, as is explained in the posts above. Matching the knife to the task done is important when you want maximum efficiency, and having the skill to use a less than ideal knife when it is all you have is important too.

 

[me2]

Great tips and info. The hissatsu has a very small secondary bevel set with an 800 grit waterstone, then finished with the sharpmaker at 20 degrees. This may be what saved the edge after the couple impacts with the ground.

I was wondering about this because my belt sander has limited power and metal removing ability. Even with a 50 grit belt, it took about 3 hours to grind a 3.5" hunter full flat from 1/8" by 1" stock. With polishing for hardening, I'm up to 4 hours. I wondered if a thicker knife could be ground with the same grinder from 3/16" stock with about a 10 degree zero bevel with a micro secondary bevel. The hunter is O1, but I was planning to switch to A2, since I think I could grind it thinner before hardening and not have any cracking trouble.

 

[wetdog1911]

Not to be OT here or even sound particulary stupid, but does the Lee book provide illustrations for what you are talking about? Some stuff I understand and others I'm making imaginary angles with my hands and going HUH?

I have a fair bit of sharpening stuff and not a clue as to what I'm doing with it. LOL My Lee Valley catalog is next to the bed. The Axe book is God knows where after my wife picked up.

Rob

 

[Cliff Stamp]

Back on point, with very aggressive abbrasives (80-100 grit AO belts) you can remove metal really, really fast even without power.

If you leave the edge very coarse you can sharpen them in a few minutes even from a dull state, not visible damage but just dull, but it takes a lot of force to get a decent cutting speed as the contact area is so high, and the work is just massive compared to working a secondary bevel. The question is why do it? Plus this isn't the edge you would use for their main promoted use which is wood craft.

Note that if you use a secondary edge bevel, then you only ever need to use x-coarse abrasives on the primary planing even when you want a polished edge, because the primary grind can be left really coarse without signficantly effecting cutting ability, especially for wood working. Lee cites studies on this in his book.

Moving to a better design also allows working with better steels. Try a puukko style knife in M2 at 66 HRC and sharpen it after serious use. The same profile with a hollow relief grind is easy to sharpen, thus you get a knife with way better edge retention than a simple carbon puukko which at the same time is faster to sharpen, and you could even make the edge more durable with a secondary edge bevel.

Are the $10 Mora's excellent knives, yes. Do they make an excellent introduction to knives with a high emphasis on cutting ability vs durability - yes. I think enough to them to uniformly recommend them to anyone wanting to begin to understand cutting ability and geometry. The stress on begin, as you should move past the puukko, which is a pure focus on edge angle and also consider other aspects of performance.

Are they the best way to make such knives - no. All I would contend about the grind is that it can be radically improved with either higher primary grinds and secondary edge bevels or hollow relief grinds depending on the required level of durability.

So, for some applications it is better, for others (like wood carving) a high polished single edge bevel (i.e zero grind) is ideal.

Ideal is the same profile with hollow relief grinds. In Lee's book on sharpening he discusses this specifically with mention to wood cutting tools, citing how the Japanese hollow grind their tools to enhance speed of sharpening.

Lap the back of a traditional western chisel and then do the same to a japanese one. Even though the Japanese steel is much harder and way more difficult to grind, you lap the back may times faster as the contact area is <1/10 that of the western one.

The same principle applies to the primary edge grind. If you think a puukko is ideal you really need to look at a similar grind with a hollow relief. That is the ideal light cutting geometry.

...does the Lee book provide illustrations for what you are talking about?

Many pictures and illustrations. If you are serious about sharpening you need to check this book out.

-Cliff

 

[knifetester]

If you leave the edge very coarse you can sharpen them in a few minutes even from a dull state, not visible damage but just dull, but it takes a lot of force to get a decent cutting speed as the contact area is so high, and the work is just massive compared to working a secondary bevel.

Yep, much faster with a secondary bevel, for the exact reasons you state, you are only removing a fraction of the metal over a much smaller area.

The question is why do it?

For a thin cutting edge, especially where it is not likely to be damaged.

Plus this isn't the edge you would use for their main promoted use which is wood craft.

You are right, for woodcraft a much higher level of polish should be used.

So, why use a mora for utility use? Because it cuts very well and is cheap. The plastic handled ones (the army model but not the 2K) have unobtrusive guards and fairly comfortable handles. They fill the hand well, but a re abit slick, a bit of traction tape fixzes this quite nicely.

Why use maintain the single edge bevel instead of adding a secondary bevel? Well, adding a microbevel to increase durability is a good idea, it is trivial to do just give the knife a few swipes on the brown Spyderco sticks at 20 degrees per side, or even 15 degrees will improve durability. That is exactly how I run some of my scandi ground knives.

However, for my utility knives, I keep the single edge (i.e. Zero grind), I sharpen them on belt sander, I just lay the entire bevel on the belt (usually there is a 150 grit on my machine), zip it across, flip and repeat until it is as sharp as you want. Time, usually well under a minute.


If there are small chips in the edge, I don't sharpen them out as it would remove too much good metal. I just leave them in, I don't care about how it looks and for the usual jobs these knives get used for it doesn't matter. If anything a few small chips will add aggression like a micro-serration. Theoretically, the area surrounding chip is weakened, and thus prone to damage, but it has not really been an issue at all.

So, you have a knife with a decent handle that you can exert a bit of pressure on with no dicomfort, a good level of cutting ability (much higher than most tactical knives), the edge holding is very good compared to most cheap knives (carbon steel at ~59RC, up to 62-63RC on the laminated ones), they are easly from a skill standpoint to sharpen since the large bevel serves as a built in jig. All this in a knife that costs under $10.

I use other knives in the same price range for similiar tasks, and they have full flat grinds and secondary edge bevels, these are recycled kitchen knives, they perform well also.

 

[Cliff Stamp]

For a thin cutting edge, especially where it is not likely to be damaged.

If this is the goal, then the hollow relief style is directly more optimal. I have such blades that can outcut puukkos several times over in terms of force needed to apply.

So, why use a mora for utility use? Because it cuts very well and is cheap.

No arguement there, they make great small utility knives, the forged carbon ones are also extremely durable. As noted I recommend them all the time, in that price range, and slightly above, the Mora 2000 is a solid field / utility knife.

... belt sander

With power equipment ease of sharpening with any steel and any profile is indeed trivial. I usually recommend that friends who use them heavily just sharpen them as normal with a secondary bevel and I recut the primary as needed, which even for heavy users is only every few months.

All this in a knife that costs under $10.

Yes you really can't argue with them at that price range, they are great working knives and there are not a lot of knives with the altered geometry described in the above at similar costs.

They are one of the knives I would like to see used as benchmarks in reviews, the Bushman for a larger knife, GB axes for chopping, martindale for larger brush work, opinels for efficient cutting, FRN spyderco's, etc., then you have the higher end benchmarks, blades like the Manix, Camp Tramp, etc. . .

One way to see the hollow relief grind as I described in the above cheaply is to take a Spyderco model with a hollow grind and hit the edge flat above the grind.

You end up with a knife ground with the same edge angle as a puukko but is many times over faster to sharpen and has less side wedging / drag / sticking. Be warned it looks like hell though.

I am going to take the Pacific Salt down like this once I finish up the EDC carry with the NIB edge and see how the steel handles a really acute edge profile, possibly the Bryd's as well.

-Cliff

 

[me2]

I've basically decided on the blade shape, but was wondering what a good included angle is for a zero bevel knife. I havent decided to make it chisel ground or double, but for the look I want, around 15 degrees included is what I come get. 7.5 + 7.5 for the double or ~15 total for a chisel grind. This seems very thin. Would a 20 degree (40 included) microbevel increase the durability enough, or maybe go 20 included with the 40 microbevel? The knife will be used for cleaning up weeds and light brush around the yard, cardboard cutting, lawn work like opening bags and cutting twine, and maybe some cutting drills for MA class. The last one is probably the deal breaker and demands an included angle greater than the estimate above, but I wanted some opinions.

 

[thombrogan]

A 15 included degree edge enhanced with a 40 included degree microbevel sounds like it will handle all but the last task. A lot of 'combat' knives have angles of 50-70 included degrees to handle a large amount of 'fudge' factor. The knife could be used as a self-protection tool with such a fine edge, but it may get mangled when used as a practice item.

 

[Cliff Stamp]

Yeah, I am with Thom there, there are two radically different stress levels in the work. The utility ones are really low, I do all of that with knives with edge angles under 10 degrees included, but if your drills include cutting into objects at high speed then even a micro bevel may not be enough because you may need a >0.010" edge to prevent rippling. It depends a lot on your skill and the consistency of the media being cut. I would simply take a cheap hollow ground knife and apply such a bevel to it, which you can do fairly quickly, and use this as a guide.

-Cliff