Recurve question

Starfish

Starfish

Joined
Jun 14, 2001
Messages
1,256
First off, would like to thank everyone for their comments on the710 vs. Military thread.

The recurve seems to be a big hit among the 710 proponents. I've never used a recurve, so I have no idea what performance advantages the recurve has.

So there's the question - what is the point of a recurve?

Thanks!

Matthew
 
Give this a gander:
http://www.bladeforums.com/forums/showthread.php?s=&threadid=90315&highlight=Axis

I post that link alot, as I found Joe Talmadge's decription of sharpening and the performance gains to be very helpful.
Simply: recurves slice far more aggressively than straight edges, and a recurve+good belly makes for great versatility (read the linked thread, Joe is alot more technical than I am:)).
I have narrowed my folders down to four, and three of them are recurves. For my uses, I find them much better performance-wise than "normal" blades. Love 'em.
 
I, too, appreciate a recurved edge -- though I despise them when it comes time to resharpen them.
 
The advantage of recurves in a folder are for slicing or slashing. The difference in performance from a non-recurved blade can be considerable.

There are two disadvantages. One is that it's more difficult to sharpen, and that you'll need something like v-sticks or a ceramic rod instead of your benchstone. The other disadvantage is that for some types of usage -- food prep, for example, having a recurved edge is a big pain. If your job is such that you have to bring the entire edge down at the same time, obviously the recurve doesn't work as well.
 
I put a recurve in almost every blade I forge lately unless my customer just absolutely 'despises' them. The recurve blade is by far the most serviceable blade geometry for a utility/camp type knife. You can cut on the push or pull stroke just efficiently. For a fighter, there is no equal in my humble opinion. Sharpening isn't that much of a problem either as long as you keep your eye on the edge as you sharpen. Follow the curve at the edge of the stone and you should have no problems.

Not every knife style benefits from a recurve though. Sometimes, like Joe said, you need a straight edge for cutting meat or produce in the kitchen. But I sure do love a nice recurve for most everything else!
 
The advantage of recurves in a folder are for slicing or slashing.
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I can sort of understand, from the link above, why the recurve would excel in these areas.

If your job is such that you have to bring the entire edge down at the same time, obviously the recurve doesn't work as well.
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I can see your point here as well. However, if a job requires bringing the entire edge down at the same time, couldn't it be done just as effectively by a push cut followed by drawing the knife ala Sharpmaker sharpening technique? (I hope I described the motion clearly)

I am a little concerned, because I am getting ready to order the 710HS, and I want to be able to carry and use this for daily tasks which will involve slicing and push cutting.

Matthew
 
Matthew -- Don't be too worried. The 710 is incredible as a general utility knife. Even push-cuts work out well, and if the material ends up being a bit too tough to push-cut through, add a little slicing motion and the recurve will make short work of it. The one obvious application where a recurve doesn't work as well is in the kitchen, where for some kinds of food prep, it's nicer to have a straight edge that will hit the cutting board at teh same time (which is why you never see recurved chef's knives). Please, don't latch onto that and let it prevent you from buying the best 4" production folder in existence. For the kinds of kitchen jobs I described, a folder isn't really the best choice anyway. In addition, there are a whole host of food prep jobs the 710 does just great with, partially for the reason you mention: you push cut through when appropriate, and can add a little slice to finish things off. I use my utility folders for food prep all the time, and the 710 remains my favorite bar none.

Joe
 
I agree with Max. Sharpening a recurve blade on the edge or corner of a benchstone is really not too much of a task at all.
 
Personally I don't like recurves. Not that they don't have their place I suppose, but except for some limited applications I don't think they are all that versitile.

They are more of a pain to sharpen. Yes you can do it on the edge of a stone, but that's not where stones are most efficient. Everyone has a problem sharpening the belly of a blade on a stone, why give yourself two bellies to worry about? Yes, stick type sharpeners work fine.

So what do recurves do well? Well they do cut rope, hose better than straight edges given a sawing motion I agree, but unless you cut these substances all day they aren't better enough to compensate for their disadvantages (IMHO of course). They aren't any better on flat surfaces like carpet, tarps, boxes, or for skinning where you use mostly the forward belly anyway. Food? No way! They might feel great slicing a tomato, but then tomatoes are pretty easy to slice with a straight edge too. Personally I think they are lousy for push cuts unless, once again, you are pushing with the forward (belly) portion of the blade in which case they are no different from any other blade with a decent belly. With a straight edge, the whole edge behind the belly behaves the same. With a recurve, you have to watch where you are applying the edge. Same is true when using a larger recurve blade to split wood (for example), and for mincing food like onions and garlic, forget it! There is a good reason why food prep knives of any kind - from fillet and boning knives to chef's knives and cleavers - don't have recurves. You also notice that most "survival knives" don't have recurves. A straight edge with a belly is just plain more useful and convenient in most applications.

So where do recurves shine? Well, if you've got to stop an attack with a quick slash to an opponent's wrist or throat, then I suppose the recurve really shines. Personally, I've never slashed any throats so I'll stick to my straight edges.
 
Originally posted by matthew rapaport


So where do recurves shine? Well, if you've got to stop an attack with a quick slash to an opponent's wrist or throat, then I suppose the recurve really shines. Personally, I've never slashed any throats so I'll stick to my straight edges.
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That's not really fair Matthew. I know where you're coming from but I have to disagree with you because of my expereince in making and using recurved blades. A recurve style blade with a flat grind is superior for free-hand leather cutting. I use one in the shop when I'm making sheaths. It's also excellent for cutting cardboard for lighting my forge. The advantage becomes clear when you look at how the edge contacts the material. Cutting rope, tape, twine... You know, all the things a utility blade shines at. These are all good uses for a recurve blade. Slashing wrists and throats? Nah, that's only for the professional knife fighters. That's not what we're all about here is it?

Please don't take this as an argument. It's definately not. I just think that maybe, just maybe, you haven't given the recurve a fair shake. Hey, I'm not going to lose any sleep or money over your preferences. I'm just trying to figure out why you're so dead set against them. Can you elaborate a little more just to humor me? I might even learn something here. Actually, you already have me thinking about your comment concerning the recurve in a survival knife. I'm trying to decide why a survival knife wouldn't benefit from a recurve edge. I'd like to hear more on your ideas concerning that. Thanks.
 
Matthew Rapaport,
My daily carry is a recurve, and I use it for food prep, even slicing loaves of homemade bread (from the bakery), at work for cardboard, heavy industrial hose, rope, around the house, and even for whittling sticks. I carried an AFCK for three years, and my CF EDC outperforms it in every aspect except tip penetration-which means nothing to me, anyway.
btw, you do not "saw" with a recurve.
Sounds to me like you haven't used one, or just don't know how to use one. I'm not saying they're the best for everything (like processing game-which I don't do), but I think you're missing out on alot of performance.

Max,
Survival knife-recurve makes it a better draw knife, gives it a sweet spot for chopping, more belly for finer cutting. Ethan Becker could probably give you some good input, since he designed the Brute with a recurve.
 
Max I know people cut differently, so I'm not sure how to compare our styles with different blade shapes. You mention things like tape and twine for example. I typically cut tape with the forward belly of my knife whether the tape is already stuck down (i.e., I'm trimming), or I'm cutting it near the roll, so I don't see how the recurve helps. Leather? I cut leather on a wooden board and find a straight X-acto style blade (or for example a wharncliff) works best, so again I don't see how the recurve comes into play. If you are holding the leather up with your hands then I can see the recurve coming into play, but it would only matter if the leather was thick. Otherwise, as with your other example, twine, even if the recurve was theoretically better the substance to be cut is so easy to cut with any sort of blade that the advantages of the recurve don't outweigh the disadvantages which was all I was trying to say.

Cardboard again I either push through with the belly of a blade, or pull the blade (up or down). It seems to work best if the blade attacks the cardboard at an angle, easy enough to provide by angling the handle. It only takes a few degrees. The recurve would actually be at a disadvantage here unless you keep the handle perpendicular to the cardboard so the recurve itself provides the angle. Nothing wrong with that, but again, its easy to angle a straight edge, so how does the recurve's advantage outweigh its disadvantages?

Lets turn to a large recurve "survival knife". I said only that most survival knives were straight, not all, but what does the recurve give you? A sweet spot for chopping? Yes, a relatively small sweet spot. That it works I fully grant, but a straight edged knife designed for chopping typically has a wider sweet spot so again I don't see how the advantages outweigh the disadvantages.

Owen, what do you mean? When I cut rope, I mean thick rope, not twine, I put downward pressure on the blade while I push it forward. I continue this downward pressure and draw backward. That's a "sawing motion" to me, and its in that backward draw that the recurve has its <i>only</i> advantage IMHO.
 
Matthew,
When you said sawing, I pictured going back and forth repeatedly over the recurved portion of the blade, like, well sawing.
You mentioned cardboard. Carboard is one place where you will see a tremendous difference with the recurve, IME. A straight blade slides right through. A recurve catches on the front recurve, and "puts a zipper in it". You can feel it catch, it's almost like you're using a Wyoming knife or gut hook.
I made a statement in a recent post in the custom forum in a thread about the Sebenza vs. EDC. I was actually referring to the durability of the ceramic peen finish, but the cutting performance was part of it, too.
I made two cuts, approximately 2 feet in length in a large cardboard container, that is several layers sandwiched together for a total thickness of about 3/4". It's thick, full of dirt, and it's hard to cut.
I made those cuts with a DDR EDC and used one hand.
I tried to cut this stuff with a small Sebenza, and barely got 1/2" into it at first. Once I got the cut started I used both hands, and my body weight to force the blade about 8" before it wouldn't go any further.
2 ft. with one hand vs. 8 inches with 2 hands and maximum effort
That's a 300% difference not even taking the added effort into account. Why? The EDC has a longer blade, but only the recurved portion was used (which is shorter in length than the small Sebenza's blade). And really, both blades were push-cutting, because the Sebenza was being pressed down, and the EDC was, too, but with the blade at an angle, and hung on the front recurve.
I don't see this level of difference on thinner stuff, but on tough cutting jobs (I try all my knives out at work except for stuff like SAKs and big fixed blades) the recurves always perform better, usually 2 to 1 or even more.
My .02
 
If you use a jig type sharpener, Lansky/Gatco/DMT, I find the recurves are not really any different than sharpening a straight edge if you already know how to sharpen a knife. As long as the stone isn't more than 1/2" wide, no problem.

The Spyderco 204 is pretty easy also.

I can see how they'd be a pain on a bench stone, or if you are using a stone that is more than 5/8" wide.

I didn't read the whole thread, but for the guy asking the question (Starfish), here is why recurve works ... imagine putting the base of a recurve folder's edge on a wooden dowel that is lying on a table. If you pull the knife towards you, a drawing and slicing motion, if you are using a straight blade, the blade will sink into the dowel to the extent that you put vertical pressure on the knife. However, with a recurve, the sloped part of the edge tends to bite into the dowel as that "ramped" part of the edge takes linear motion (your hand pulling) and translates some of that horizontal energy into a vertical cutting motion. The blade wants to "ride up" that upward ramp of the recurve...that forces it into the dowel. Hope that makes sense... hard to describe in text.
 
rdangerer,
That was an excellent description, and beat all that crap I had to type to try to get a point across.
 
Originally posted by OwenM
Matthew,

You mentioned cardboard. Carboard is one place where you will see a tremendous difference with the recurve, IME. A straight blade slides right through. A recurve catches on the front recurve, and "puts a zipper in it". You can feel it catch, it's almost like you're using a Wyoming knife or gut hook.
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Right, that sums it up for me. I think, as Matthew pointed it, this is somewhat a matter of what technique is used to cut. With a recurve, if you can avoid using the front belly and instead use the recurve itself -- which is what makes the recurved edge really shine anyway -- that's where you'll see the performance difference. I don't cut cardboard on the front belly; if I did, I wouldn't see any difference between a plain and a recurved blade. What I do is catch it in the recurve, where the curve itself feels like it forces the material into the edge. That is where you see the performance.

I cut almost everything in the recurve! I razor-polish the front belly and just use it for push cuts, occasionally opening mail, etc.

Joe
 
Recurve:

Advantages:
1) Longer edge length per given blade length (e.g. your 3" blade may have a 3.5" cutting edge)

2) Helps to improve the angle of incident. When cutting the curve of the blade reduces the amount of blade edge that is in initial contact with the surface you are cutting. This allows you to bring more force to bear on a smaller area, and makes cutting easier.

3) As with a billhook, the shape of the blade helps to retain soft materials. This improves efficiency when cutting depends on blade velocity.

4) On larger fixed blades the recurve helps to move the mass of the blade forward. Even if your knife is balanced at the hilt the mass of the blade is centered towards the point. This helps to build momentum during the swing.

The only real disadvantage is that you have to adapt your techniques a little to make the most out of the recurve.

N2S
 
I guys. I fully grant that the recurve has advantages. First a little more edge length for a given blade length. Some kinds of serrations also exhibit this effect, and if a single recurve is good, think of what a Kris style blade might be like on a small knife :) The other advantage is the gut-hook effect mentioned by Owen, and I grant that too. Now having granted these advantages I still say that in general, and taking into account all of the types of cutting a real general purpose "utility knife" is called upon to do, the advantages of the recurve don't outweigh its disadvantages, and remember all of this is <b>IMHO!</b>

The recurve shines in two kinds of cuts (not counting slashing in self-defense applications). One is the draw upwards as in pulling the knife up through thick cardboard (or for example carpet) where the gut-hook effect comes into play, and the other is the pull cut across some substance (like thick rope or the aforementioned dowel) that is not trivial to cut through in a single stroke with any knife (like twine would be). In this case both the extra edge length and angle-of-attack advantages come into play.

But what about the disadvantages? Difficult to sharpen on a benchstone (even a relatively narrow one using a jig IMO); no good at push cuts where the whole edge must meet the cutting surface at the same time as in dicing vegies; not very good for scraping if you want to use all or most of the blade behind the belly (taking scales off fish, hair off hide, or plaining wood where the advantages of the recurve actually become disadvantages); not good for thin slicing meat or bread because the center of the belly hits the cutting surface before the rest of the edge has cut through what ever it is you are slicing; or for any application where you must turn the knife (change direction of the cut) with the tip embedded in the substance (for example coring an apple). Add to this that the recurve only comes into its own when the substance to be cut is non trivial - for example thin cardboard is so easy to cut with any knife that the gut-hook effect while present is overkill.

So for me (again, just my opinion), taking all of this into account, the recurve makes little sense and I don't buy them. If the knife is primarily intended (and sold) for "self defense" as many "tactical knives" are, and in addition, your self defense style favors slashing (the recurve has no advantage in thrusting), then by all means buy a recurve. If, on the other hand, the knife you carry might have to do any of the chores listed above and/or you don't spend all day pulling knives through thick cardboard or sawing through thick rope, then consider a non-recurved blade.
 
How big an old boy are you anyway Matthew? Do I need to bring a sack lunch? He he. Just kidding.

I've thoroughly enjoyed our recurve discussion. I've learned something here. This is what this forum is all about anyway isn't it? It gets us to thinking about all manner of different things that we wouldn't normally think about. You make alot of good points Matthew. So do I and several of the other pro-recurve dudes in this thread. No winners, no losers. We are all winners on a topic like this. Hey, that's why I'm here. Thanks for sharing your opinoins Matthew. You're a sharp fellow with a keen interest in blade geometry. I'd like to meet you and have a chance to do a few domonstrations for you and let you do some for me.

This is a great place isn't it?
 
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