Why are most folders concave/hollow ground?

[SpyderEdgeForever]

Ofcourse there are exceptions, such as in Spyderco with saber-grinds, but in general it seems to me that most fixed and folding knives, but especially folders, tend to lean towards hollow grinds. Do you all notice this as well, and if yes, why is that? Does it have to do with ease of production machinery, with marketability and consumer desires, or a mix of factors? I mean, I understand some of the reasons for a hollow grind, but, it seems to me to be weaker than a convex grind, such as a Scandi or Saber grind.

I have seen knives that I would love to have a convex or saber grind but instead, are hollow-ground. One example: The Swedish knife company EKA, who make folders. Unlike the Mora knives, which mostly use convex and scandi grinds, the EKA folders such as the Swede 10 tend to have hollow grinds.

I also notice most cooking knives have flat-grinds. Is this due to ease of sharpening and cutting through the plant and animal tissues of food?

[defenestrate]

In many cases, I would thinnk that grinding on a wheel lends itself to hollow grinds, but I don't know whether that is the primary reason for it.

[kbuzbee]

All grinds have strengths and weaknesses. The hollow grind is designed to allow a blade to be very thin behind the edge (to improve cutting) while utilizing thicker stock for blade strength. To make a FFG as thin behind the edge you'd need a much thinner spine and the blade would be more easily bent.

Whether this design works best for you depends on how you use the knife and what you're cutting. If you are slicing through a thick, stiff material a hollow grind can be more prone to binding than a FFG blade (but there are a lot of factors)

There are also hollow ground blades designed to assist in sharpening, where you basically lay the blade flat on the stone, similar to how you hone a straight razor. In this way it sets your angle for you. Though these seem very uncommon today.

Certainly aesthetics play a role as well and the popularity of each grind style seems to come and go over time, and manufacturers try to anticipate what their customers are going to want.

As you say, automated manufacturing processes are a factor as well and you'll find machines that can hollow grind both sides of a blade at the same time, improving efficiency. But the hollow ground blade predates these processes and has its reasons for existing on its own merits.

Ken

[The Deacon]

Probably just carry over from all the advertising by kitchen cutlery makers decades ago claiming superior performance for hollow ground kitchen cutlery.

[Trout Hound]

There are also hollow ground blades designed to assist in sharpening, where you basically lay the blade flat on the stone, similar to how you hone a straight razor. In this way it sets your angle for you. Though these seem very uncommon today.

I don't think there are any hollow grinds, straight razor or otherwise, where you lay the entire blade flat on a stone to sharpen. Otherwise, you would be grinding away at the shoulder of the blade and eventually changing the angle, not to mention scratching the whole thing up. I believe you may be referring to a Scandi grind, as on a Spydie Bushcraft or a Mora, where the blade is left at a uniform thickness most of the way down, and then a single wide bevel is ground in about the bottom third of the blade. The wide bevel is then laid flat on a stone for sharpening. These are actually still used quite a bit, as they make for excellent field knives, but it is not a hollow grind.

[kbuzbee]

I don't think there are any hollow grinds, straight razor or otherwise, where you lay the entire blade flat on a stone to sharpen. Otherwise, you would be grinding away at the shoulder of the blade and eventually changing the angle, not to mention scratching the whole thing up. I believe you may be referring to a Scandi grind, as on a Spydie Bushcraft or a Mora, where the blade is left at a uniform thickness most of the way down, and then a single wide bevel is ground in about the bottom third of the blade. The wide bevel is then laid flat on a stone for sharpening. These are actually still used quite a bit, as they make for excellent field knives, but it is not a hollow grind.

No, it was an older style knife. The one I'm thinking of was not some high end blade, but needed to be very sharp. You're right, sharpening it did wear the spine, but, like a straight razor, not significantly. Iirc they were used for paper trimming or some such, back before there were X-acto style knives.

Agreed you wouldn't generally want to sharpen a modern hollow ground blade this way. I doubt the modern geometries would even support this, unless it was a custom piece designed to be sharpened this way. It was just one example of "why are there hollow ground blades?" beyond manufacturing efficiency.

(Edit - yes, that is exactly how you hone a straight razor. OCD people that we are today, we'll frequently tape the spine to prevent wear, but that was never the way they used to be honed.)

Ken

[Evil D]

I have no idea, but I do prefer the looks of a nice high hollow grind, I just prefer the performance of FFG by a long shot. I'm sure it has a lot to do with cost.

[kbuzbee]

I have no idea, but I do prefer the looks of a nice high hollow grind, I just prefer the performance of FFG by a long shot. I'm sure it has a lot to do with cost.

Agreed, David. There are a few uses where hollow ground can out perform FFG, but they tend to be shallow cuts, like trimming string. Over the wide range of typical EDC tasks, I'll take a nice FFG any day.

Ken

[Evil D]

I have no idea, but I do prefer the looks of a nice high hollow grind, I just prefer the performance of FFG by a long shot. I'm sure it has a lot to do with cost.

Agreed, David. There are a few uses where hollow ground can out perform FFG, but they tend to be shallow cuts, like trimming string. Over the wide range of typical EDC tasks, I'll take a nice FFG any day.

Ken

I'm still waiting for Spyderco to make a full hollow ground blade, ground by a very large diameter wheel so the curve is very shallow but still results in a blade that's thinner behind the edge than you can safely achieve with FFG. If the diameter is large enough, it would greatly reduce the wedging that hollow grinds suffer from, especially if the entire blade was ground as opposed to leaving that big section of flat stock at the top. Otherwise if they just did a high hollow grind in this way on a blade that's very tall, you would end up with a similar effect. My biggest gripe with hollow grinds is that they typically use small diameter wheels and are usually low to mid height on the blade as a result. Increase the diameter of the wheel, grind more of the blade hollow (even more than Chris Reeve does), and I think more people would like hollow grinds and I think the market for FFG would shrink.

[kbuzbee]

I'm in for one of those!

Ken

[SpyderEdgeForever]

If you compare a Saber or Scandi grind to a FFG, which one outperforms the other for general cutting purposes, though?

[Evil D]

If you compare a Saber or Scandi grind to a FFG, which one outperforms the other for general cutting purposes, though?

Well, if we compare a flat ground saber (as opposed to a hollow ground saber) to a scandi, they're very similar in appearance except that the scandi grind has no secondary bevel, it transitions right into the very edge. Because of this, it will almost always be thinner behind the edge than the flat ground saber, so that's your answer. All that aside, you still have to consider blade height/thickness/height of each grind/etc as those are variables that can easily sway the advantage to one or the other.

[Sequimite]

The main answer, according to a number of knife makers I've talked to was hinted at by EvilD but goes beyond and is related to being thin behind the edge.

Most humans for most of history have been lucky to afford a single good knife. Working intensively with a single knife means that it must be resharpened often. As the blade wears away in a hollow ground it stays thin behind the edge for a long time whereas a FFG gets much thicker behind the edge much faster. A saber grind is even better but is much harder to sharpen because of the amount of steel that must be removed. The hollow ground blade gives the most service compared to the amount of maintenance for a practical user.

[Evil D]

The main answer, according to a number of knife makers I've talked to was hinted at by EvilD but goes beyond and is related to being thin behind the edge.

Most humans for most of history have been lucky to afford a single good knife. Working intensively with a single knife means that it must be resharpened often. As the blade wears away in a hollow ground it stays thin behind the edge for a long time whereas a FFG gets much thicker behind the edge much faster. A saber grind is even better but is much harder to sharpen because of the amount of steel that must be removed. The hollow ground blade gives the most service compared to the amount of maintenance for a practical user.

And when you consider hollow grinds like CRK use, which are actually thinner behind the edge than the edge bevel itself is, you get a knife that gets easier to sharpen and will slice better the more you sharpen it, up to the point where you start to transition into the wider area of the grind, but by then you've gotten so far up into the blade that you're getting close to retirement. This is the one single reason I would choose a hollow grind over a FFG, it's just too bad that very few people make a hollow grind like CRK do. It's also one of the constant nagging temptations that haunt me about buying a Sebenza.

[xceptnl]

And when you consider hollow grinds like CRK use, which are actually thinner behind the edge than the edge bevel itself is, you get a knife that gets easier to sharpen and will slice better the more you sharpen it, up to the point where you start to transition into the wider area of the grind, but by then you've gotten so far up into the blade that you're getting close to retirement. This is the one single reason I would choose a hollow grind over a FFG, it's just too bad that very few people make a hollow grind like CRK do. It's also one of the constant nagging temptations that haunt me about buying a Sebenza.

I have been considering a regrind of my saber ZDP Delica for years. I want to have it done with either a 36" or 42" radii platen. This works for custom knives, but I don't think it would do for a large scale production shop. As you stated earlier, large wheels would have to be used. I do love the way my CRK Sebenza cuts and the Dragonfly Salt is the only Spyderco I have found that has a grind to rival the small Seb.