Does the grind of a blade make a big difference in sharpness?

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DanMan4142

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Feb 16, 2004
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I am wondering if there is a very significant difference in the final sharpness of a knife based on its grind. I understand that a hollow grind will slice better than a flat grind due to the fact that it is thinner, but does that also make it sharper at the edge? I have a gerber gator hunting knfe with a hollow grind that has the sharpest edge of any of my knives. it will shave hair without even touching my skin. I can get my other knives to shave, but not nearly as well as this hollow ground gerber(my only hollow ground knife).

thanks

Dan
 
It is my understanding that with a hollow grind, the actual cutting edge angle becomes very small. Thus the blade can in theory be very sharp but somewhat delicate, and thus prone to damage.

It would be interesting to take your favorite hollow grind blade and try to measure exactly what the edge angle is.

To do this one would need an EdgePro sharpener that has infinitely adjustable angles to attempt to match up with your blade.

Once the angle was established it could be duplicated on another knife with a conventional grind, and both knives compared. I suspect they would cut and wear the same.
 
A hollow-grind is fine for sharpness, since it can produce a blade that is narrower just behind the edge bevel. That same grind also makes it easier to sharpen the edge, since you have less metal to remove. If shaving is your goal, that's just fine.

But slicing dense materials is another matter. The hollow-ground blade tends to bind as the depth of the slice reaches the wedge near the spine of the blade.

In testing the hollow-ground blade of the Spyderco Persian, I sliced the very dense cardboard of the carton that my lawnmower was packaged in. The Persian blade choked very badly, while both the Benchmade 806D2 and the Spiderco Military blades easily sliced through the same material.

The difference in slicing properties for these three blades was much less dramatic when slicing thinner cardboard (a cardboard beer case).
 
Just to clear things up (maybe muddle it more) there's a lot more to sharpness than what has been said so far.

You have basically three types of grinds - flat, hollow & convex.

Then, there are 2 areas to grind - the blade and the edge.

One of my favorite knife styles to grind is flat ground with a small convex edge. But it's completely different from the full-convex grind knives I also make.

Most factory knives have a flat + flat combination grind. That means that the blade is flat and the edge is flat.

Why do I bring this up?

Because blade grind has a lot to do with cutting too. A thicker blade (no matter what the grind) is going to have a more difficult time passing through materials than a thinner blade (in a low effort cut - as posed in an earlier post).

Why use a thicker blade then? For additional strength in impact cuts - chopping, for example.


As stated, most production knives have a flat edge grind. A handmade knife can either of the 3 types.

If the knifemaker used a wheel to put on the final edge - you have a hollow-ground edge.

If they used a belt on a platen, then you most likely have a flat edge.

If they used a strop, or a slack belt, then you have a convex edge grind.


I had a knife that was made of ATS-34 and at the time was my sharpest knife. It had a hollow blade grind, with a convex edge grind. Sailed through everything lickedy-split. But that had more to do with the well-hardened ATS-34, than the blade geometry....yet again, one more thing to consider. Different steels hold the edge better. Generally speaking, handmade knives heat-treated by professionals hold their edges better.



So - there's no single "best grind".....no "best steel"....no "sharpest blade geometry".

Just have to do your research and find out what will work best is your particular way of using the knife. When you bring all the elements together properly, then you get an oustanding knife.
 
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Everything he said. Dan knows sharp blades, as anyone who has seen his work can attest!
 
Normally I would say that edge shape has no effect on blade sharpness, at least not for normal usage. You can get a razor sharp edge on a convex grind as well as a hollow or flat grind.

However for specialty uses a full flat grind with no microbevel on the edge can be sharpened sharper than any other grind that I have seen. I once had a person have me make a full tapered (spine to edge) knife from 1 1/2" wide 1/16" thick 440C. The end result was an edge that flexed all over the place when it came time to sharpen it...I did my best, a full razor edge. The customer said it wasn't sharp enough, I was about to debate that point until he took another out of his pocket and began to shave the ridges off the tip of a finger print and displayed them on the surface of the blade perfectly arranged.........that was sharp. He admitted that it had taken some time with a collection of water stones.

The edge was definitely not strong and would chip easily but it was incredibly sharp.
 
Does the grind of the blade make a big difference in sharpness?

No, all the different grinds can and do reach a great sharpness, but the grind does make a difference in how well the knife keeps that sharpness and/or how often it needs touched up or re-sharpened.

From my experience a convex ground blade will retain its edge longer but is harder to get back and trickier to do correctly than a conventional hollow or flat grind. Most of the Scandinavian grinds are very tricky to do correctly also due to the way the edge is zero degree on them. I've witnessed many guys at the gun shows that do sharpening for people take these Scandi knives from customers and just put a good ole 'American' edge on them by beveling the blade and have often wondered if they bothered to even think about what they just did to that knife.

The type of steel and the hardness also plays into the difference in how sharp a knife is of course. But the real tell is from getting to know what type of grind fits your lifestyle best I think. If you are one like me that makes walking sticks and uses your camp knife to debark tree limbs then a convex grind probably won't be the knife you want to use as they don't exactly slice right for this type of job. Flat grind would be more durable for this, hollow would work but the edge would most likely suffer more from the abuse than a flat grind would. However for chopping down the tree the convex would be the best knife for the job.

For skinning and field dressing type of activities one could say any of the three primary grinds would work fine. I know a lot of guys that are using convex grinds for this and like it. I like my Dozier hollow grind for this task but I've used both. Next deer season I may be using a Bark River convex and comparing it to the way I've been doing things and comparing A2 to D2 should be an interesting experience. I have a Marbles Hunter that I'm sure was ground by Mike Stewart. It is sharp but it doesn't slice well on some harder materials. It does slice well on flesh though. Dulling it takes quite a while too. My D2 blade from Dozier keeps an edge better than any I've ever used and it is hollow ground. I would bet a D2 Convex with proper heat treatment would be an awesome edge retaining knife.
 
george tichbourne said:
Normally I would say that edge shape has no effect on blade sharpness
Click to expand...

The only way it has an effect is that if the angle is so acute, the carbide structure of the steel influences the process. If you take D2 for example, or something very coarse and sharpen it at very low angles, ~5 degrees per side, the edge will look different than 52100 at ~5 degrees per side because the carbides of D2 are 30 x larger.

Of course this has nothing to do witht he primary grind, it is the secondary or edge grind. It is easily possible to get hollow grinds with thick edges, and thus have flat grinds with thinner profiles. In the extreme limit a hollow grind has the ability to be thinner thana flat, which has the abiilty to be thinner than a convex grind - but this doesn't mean they are, it depends on how the knife was ground.

-Cliff
 
If all you are measuring is shaving ability then a hollow ground edge will get the sharpest and be the easiest to resharpen (as long as your knife blade is thicker than a razor blade). What you have resembles a blade with two parts, the spine of the blade is thick and you have a virtual razor blade between the spine and the edge. I would say at least 95% of straight razors produced in the last 100 years were hollow ground for optimal shaving sharpness and ease in resharpening. So if all you are concerned about is impressing your friends by shaving arm hair, carry a straight razor.

On the other hand most of us actually cut some cardboard now an then. The straight razor's edge would be damaged if used for that, the spine of the blade would drag, and the handle is almost useless for that purpose. A thin hollow ground knife would work fairly well, but most commercial hollow ground knives are a bit thick and wide which increase drag. A thin full ground blade with an accute secondary grind angle with just a little convexing gives you good shaving ability and low drag. For most purposes you don't need a thicker blade for strength, but you do need to widen the convexed area of your final edge to increase its lateral stability. If you chop with the blade it needs to have a more obtuse primary (blade) grind to keep the edge from rippling. A machete is not real thick, but has a somewhat obtuse grind. As long as the blade is hard enough (in the low 50's RC) the edge will not ripple too much.
 
The best straight razors are actually 1:1 hollow ground which is a different grind than a regular hollow ground (there are also 1:2 and 1:4 hollow ground). A regular hollow ground would be so sever on a straight razor that the edge would lack stiffness. So 1:1 hollow ground uses a double hollow ground: One on the main part of the blade and a second one close to the edge, which results in a thickened part in between the two grinds which runs parallel to the edge all along the blade about 3 mm from the edge. This gives a unique elasticity to the blade suited to shaving and minimizes the necessary material removal for sharpening.....but it doesn't make the edge any more or less sharp than a regular hollow ground.
 
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