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WHAT....makes a serrated edge cut so good?
- Thread starter Lavan
- Start date
The Tourist
Banned
- Joined
- Dec 23, 2001
- Messages
- 2,796
I'm not convinced that they are better, but I do see their application. I think a hard use knife with serrations that is carried a lot, then used rarely and only during rescue events, might benefit from a serrated edge. There are many reports of such knives cutting through seats and seat belts to save crash victims.
When I first got into knives I ordered everything in combo. It didn't take me long to realize I needed a longer straight edge. Also, I bought an Edgepro, and straight edges are easier to sharpen. My Strider AR could easily cut a seat belt, but I'm not an EMT, so the odds lessen.
I did have one totally serrated knife, a Jot Singh Kalsa. I got a deal on it, and I carried it as an EDC for a few months, backed up by either a Microtech Mini-SOCOM or an Opinel. This JSK cut like a chain-saw, but the edge was never very neat. I had a female friend who along with her mother managed an apartment complex. She liked the JSK, and when she needed to cut something it was rope or cardboard or wood slats; neatness didn't count. I gave her the thing, and it had many useful years.
When I first got into knives I ordered everything in combo. It didn't take me long to realize I needed a longer straight edge. Also, I bought an Edgepro, and straight edges are easier to sharpen. My Strider AR could easily cut a seat belt, but I'm not an EMT, so the odds lessen.
I did have one totally serrated knife, a Jot Singh Kalsa. I got a deal on it, and I carried it as an EDC for a few months, backed up by either a Microtech Mini-SOCOM or an Opinel. This JSK cut like a chain-saw, but the edge was never very neat. I had a female friend who along with her mother managed an apartment complex. She liked the JSK, and when she needed to cut something it was rope or cardboard or wood slats; neatness didn't count. I gave her the thing, and it had many useful years.
- Joined
- Apr 27, 1999
- Messages
- 6,117
There are a lot of reasons why serrated knives slice effectively (not neatly, but effectively). The first is that the points of the serrations apply a lot of pressure at their tips to start penetration in the cut material. The next is that your slicing stroke plows those serration tips across the surface layer of the material. The force your applying is again concentrated only on the serration tips. This allows more concentrated force to split the material apart where the tips are working. You partially get a ripping effect like with paper. Once you get a rip started it is easier to widen it than it was to start it.
Another advantage is that the upslope of the sides of the serations plow through the material as you slice. This is a good angle for cutting sideways. The material is weaker when you are working sideways across the surface. It is not supported at the surface. When you press down in cutting soft material levels out the load and clings to the side of a blade. Most materials can't conform as well and aren't as strong when you plow through them sideways. The serrations are plowing or cleaving and ripping their way through the material.
When you cut rope the tips of the serrations do less of the work. The sloped sides of the serrations work to cut subsets of the fibers at a time. With a smooth edge the fibers mash down together into almost a continuous surface. The work of the edge is spread out and is mainly trying to abrade through the abrassion resistant fibers. With a serrated edge you are attacking smaller groups of fibers that you are pushing sideways out of the central mass of the rope. The sides of the serrations are in position to cleave these fibers rather than slice them.
Serrated edges keep most of these advantages even when they are somewhat dull. They never do as neat a job as smooth edges, but they do help you to hack things apart.
Another advantage is that the upslope of the sides of the serations plow through the material as you slice. This is a good angle for cutting sideways. The material is weaker when you are working sideways across the surface. It is not supported at the surface. When you press down in cutting soft material levels out the load and clings to the side of a blade. Most materials can't conform as well and aren't as strong when you plow through them sideways. The serrations are plowing or cleaving and ripping their way through the material.
When you cut rope the tips of the serrations do less of the work. The sloped sides of the serrations work to cut subsets of the fibers at a time. With a smooth edge the fibers mash down together into almost a continuous surface. The work of the edge is spread out and is mainly trying to abrade through the abrassion resistant fibers. With a serrated edge you are attacking smaller groups of fibers that you are pushing sideways out of the central mass of the rope. The sides of the serrations are in position to cleave these fibers rather than slice them.
Serrated edges keep most of these advantages even when they are somewhat dull. They never do as neat a job as smooth edges, but they do help you to hack things apart.
- Joined
- Feb 12, 2002
- Messages
- 1,525
I found this explanation, about what makes a serrated edge cut better in regards to the SpyderEdge, at the Spyderco website. 
(Sorry for the poor diagrams.)
_____________
"Because serrations improve cutting ability. The tips of the serrations provide single point penetration at the same time the center of effort rotates around each serration for an infinite number of cutting angles, increasing the cutting edge length by up to 10%(Diagram B). A serration is a sharpened recessed curve along the edge of the blade and has more linear cutting surface than a straight edge in the same space (Diagram A). And, serrations improve edge retention because the tips initiate the cut easing the amount of force required by the recessed edges. The points actually protect the sharp inside curves that continue the cut, thus the curves have less wear over time. Our signature SpyderEdge, also referred to as a two-step serration incorporates a repeated pattern of one large and two small serrations(Diagram B).
There have been many variations of serrated edges produced over the years. Even a properly sharpened plain edge will exhibit vertical scratch patterns with "micro-serrations" that enable the edge to cut efficiently(Diagram C)."
_____________
(Sorry for the poor diagrams.) _____________
"Because serrations improve cutting ability. The tips of the serrations provide single point penetration at the same time the center of effort rotates around each serration for an infinite number of cutting angles, increasing the cutting edge length by up to 10%(Diagram B). A serration is a sharpened recessed curve along the edge of the blade and has more linear cutting surface than a straight edge in the same space (Diagram A). And, serrations improve edge retention because the tips initiate the cut easing the amount of force required by the recessed edges. The points actually protect the sharp inside curves that continue the cut, thus the curves have less wear over time. Our signature SpyderEdge, also referred to as a two-step serration incorporates a repeated pattern of one large and two small serrations(Diagram B).
There have been many variations of serrated edges produced over the years. Even a properly sharpened plain edge will exhibit vertical scratch patterns with "micro-serrations" that enable the edge to cut efficiently(Diagram C)."
_____________
I've found that serrated work better on certain materials and straight edges work better on others. As an ex-commercial diver, I can tell your that serrated knives are much better at cutting rope, particularly wet rope than straight edges. When I first started diving I carried a straight edge that I religiously sharpened to a razor edge. One day an old Navy diver asked to borrow my knife to cut a rope out of a ships wheel (prop). After he looked at my knife I was horrified to see him take a course carbide stone out of his bag and rework the blade to where the point where it had a sharp but rough edge. After he finished the job he explained that the rough edge tended to push the cut fiber out of the way to allow the blade to get to the uncut fibers. Lesson learned. When serrated blades became popular I bought several Spydcos and still carry them as my primary dive knife.
On the other hand, I would not use one to clean game, do wood carving or any of a number of other things where a smooth straight edge works better. Just MHO from a new member to the list.
On the other hand, I would not use one to clean game, do wood carving or any of a number of other things where a smooth straight edge works better. Just MHO from a new member to the list.
Allen E. Treat
Banned
- Joined
- Oct 4, 2001
- Messages
- 498
Maybe it's the cut you get when you cut yourself with one.
AET
AET
- Joined
- Jul 22, 2000
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- 981
No sh*t! My thumb knuckle was in the way as I was closing my SOG Magnadot once and the serrated part came down on it like a Ron Popeil slice 'n' dicer!
The lockback spring gave it enough propulsion to give me a nasty cut.
FTC
Tip: Krazy glue makes for good blood clot and band aid.
Just gotta look at serrations as being a MAGNIFIED regular blade. Since under a microscope even a plain edge would look serrated, it just makes sense that more of what makes cutting would make more cutting. And bigger would be faster. Never thought it through before.