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Wesley Alberson

How useful are recurve designs?

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I have had this question on my mind for a while. I have made recurve knives before, and I love the way that they look, but I'm not sure how much more useful it is when compared to a knife with a belly.

So from what I can gather, the main purpose of a recurve blade is to have a more extreme curvature out towards the end. The extreme end of this design concept is something like a dane axe. There is no recurve, only an extreme curvature at the end of a long stick. A step down from that would be something like a kopis or kukri, where the blade is sharpened down the whole length, but the sweet spot of the blade is towards the end with the outwards curvature. I guess the sharpened inwards curvature could be useful for really close situations.

One thing that I noticed about kukris, at least the one that my mentor had, is that the outside curvature is the only place that is sharpened. He got it as an antique. In the case of something as long as a kukri, it makes sense to have a recurve because it is a long chopping blade that benefits from having a belly further away from the handle. On smaller knives that don't have the forward weight and momentum to be a chopper, is it really necessary to have an inwards curve? If you took a recurve blade, and drew a straight line from the start of the edge so that it is tangent to the belly of the blade (essentially filling the recurve part so the curvature is positive), wouldn't it cut the same? This question has no clear cut answer like many design questions, but it is interesting to discuss. 

I think the polar opposite of a recurve blade would be something like a sickle sword, where the point can be used like a spike, and the blade can hook and grapple. The miniaturized version of this design concept would be a sickle or karambit.

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I've made 4 Kukris now, just my interpretation having nothing but photos to go on.....

My opinion, in the case of a Kukri recurve is not the correct term, I see it as a bend in a blade that takes a knife halfway towards being an axe.....

As far as recurve blades are concerned, two things are not in doubt: Their sexiness (JMO :D ) and their cutting ability....... I understood it when I nicked myself with a recurve blade, the cutting edge suddenly was where I didn't expect it to be and it bit.....

The only issue on smaller recurve blades is the sharpening......depending on how you sharpen.....

Edited by Gerhard
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As with any tool, there are different configurations optimized for different uses.  I would never try to replace a chef's knife made for cutting on a flat board with a recurve blade, but a slight recurve certainly appears to have some advantage in cutting free hanging items.  I believe this is a combination of the increase in cutting edge length per relevant length of blade as well as the geometry of the edge to object to be cut orientation during a swing/slice cutting operation.  Cutting involves both dragging the sharp edge across the object to be cut (slicing) as well as providing a force vector down on the object (chopping and progressing the slicing cut).  For some cutting activities a recurve seems to coordinate well with the ergonomics of knife use to make the cutting more efficient.

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22 hours ago, Gerhard said:

I've made 4 Kukris now, just my interpretation having nothing but photos to go on.....

My opinion, in the case of a Kukri recurve is not the correct term, I see it as a bend in a blade that takes a knife halfway towards being an axe.....

As far as recurve blades are concerned, two things are not in doubt: Their sexiness (JMO :D ) and their cutting ability....... I understood it when I nicked myself with a recurve blade, the cutting edge suddenly was where I didn't expect it to be and it bit.....

The only issue on smaller recurve blades is the sharpening......depending on how you sharpen.....

That is an interesting perspective, I can definitely see kukris as being pinched and bent rather than having a recurve. The cutting ability of a recurve is great indeed, It is almost like a thin and sharp club.

16 hours ago, Dan Hertzson said:

As with any tool, there are different configurations optimized for different uses.  I would never try to replace a chef's knife made for cutting on a flat board with a recurve blade, but a slight recurve certainly appears to have some advantage in cutting free hanging items.  I believe this is a combination of the increase in cutting edge length per relevant length of blade as well as the geometry of the edge to object to be cut orientation during a swing/slice cutting operation.  Cutting involves both dragging the sharp edge across the object to be cut (slicing) as well as providing a force vector down on the object (chopping and progressing the slicing cut).  For some cutting activities a recurve seems to coordinate well with the ergonomics of knife use to make the cutting more efficient.

That makes sense with cutting free hanging items, the inwards curve kind of "gathers" the material so it applies more force to an object in mid air, rather than just letting it slide across one large outwards edge.

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For larger blades, the recurve is also for structural reasons. It's a bit like a half leafblade. You have the widest part of the blade right were you need the highest in plane strength, and the thickest part near the hilt right were you need the most out of plane strength and stiffness. For a shorter blade of a material that is relatively soft, this gives the strongest blade shape. And as an added bonus, it also cuts a lot better. 

For a short blade, it gives a different edges types for different uses in a single blade. That's why you see recurves a lot in bronze age knives, where they were usually limited to one knife to do everything with. 

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