design feature toughness

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chad2

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I am looking into more design features not steel types, that make a very useable and tough knife. What are some features that make a knife tougher design wise like all rounded edges, no jimping, distal taper, and drop point blade.

What are some other little features that help with toughness and make a knife more user friendly
 
I am no where near as knowledgable as most guys here but the only advice I can give you is No Finger Choiles on the handle . They are not comfortable .
 
differential heat treat, thick spines, no grind lines. full tang. man-made materials like g10 or micarta. higher temper heat then is required (lower rockwell hardness)
 
You're asking at least two different questions.

In terms of a knife that can take a beating, it's simple; more steel is more stronger. All else being equal, a 1/4" bar is much less likely to break than a 1/8" bar. Everything you cut/grind away makes it more susceptible to breakage... especially if that feature is pointy or has a tight radius, like jimping or a square plunge line (look up "stress risers" for further info).

I remain thoroughly unconvinced of the popular claim that distal tapers make a blade "tougher". More flexible? Yes. Cut better, and improve balance? Yes. Does removing steel from the tip somehow magically make it stronger? Ask most bladesmiths and you will likely get one answer... ask a few mechanical engineers and the answer will be quite different.

If you want to really get into this, look up "modulus of elasticity".
 
Toughness is a factor of both steel type and design. First, pick the steel that meets the toughness required. Then design the knife to allow the degree of toughness needed.

As James said, if all you want is the toughest knife possible, take a bar of 1.5"X.25" 3V and made the tip round. Give it a sabre grind with no plunge, and put on G-10 scales. It will be ugly and heavy sharpened bar of steel, but it will be a tough knife. This is basically what the Graham Razel is.

Distal taper has nothing to do with toughness. It is a feature affecting flex and balance......not toughness.
 
very valid reasons but in some ways i dissagree in a friendly way. here are some very rough pics i made to explain first by removing material you can strengthen certain structures. this does not go for everything but in our case there are ways to strengthen a knife. these are two different ideas on how removing material can actually make a structure stronger or less prone to breakage how ever thick or thin the material.

when i say strength what i mean is to prevent from breakage because in a chopper design knife you want something light enough to wield, heavy enough to dig into the material, comfortable, and maybe not flexable but something that if it were to flex wont break.

the first and second pics here is obviously not a knife but this shows how in many different ways removing material from and exsisting design can produce strength
qi2s.jpg


aoyd.jpg


the third one here is not a perfect pic but it is a design that i have been looking into that i would like to implament into my design to prevent from breakage around the plung grind.
n07m.jpg
 
You are correct about distributing stresses, as shown in your first and second drawings. So yes, in that very specific instance removing material can indeed improve strength. But that's kind of a robbing-Peter-to-pay-Paul approach.

If that inside angle had been properly designed and left with a radius to begin with, instead of being cut to a right angle or adding a stress-relief zone, it would be much stronger than either. More steel is more stronger. Period.

Your third drawing is also correct. Some makers (including myself from time to time, and Rick Marchand almost always) do indeed make plungeless knives exactly for that reason.

Just to be clear, none of that has anything whatsoever to do with the question of distal tapers, though.

Of course, since we're blessed with some very tough alloys and HT regimens today, we can balance design features with inherent material properties to get knives that perform very well and are very tough. :thumbup:
 
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Distal taper generally means thinner tip. Given that it is frequently the tip that breaks when a knife is subjected to rough use it is not always a good idea. Ed Fowler uses "reverse" distal taper for this reason. On a short rough use knife no taper or even reverse taper is probably a good idea if you intend to wail on that knife. Distal taper looks good, and helps balance, but I would disagree that it makes a knife tougher in the context of this discussion. More flexible, yes. More likely for the tip to snap off, also yes.

Weight towards the tip increases the moment of inertia. Good on a chopper, bad on a fighter, annoying on a skinner or utility knife. So there are always compromises in a design.
 
Nathan the Machinist said:
Distal taper generally means thinner tip. Given that it is frequently the tip that breaks when a knife is subjected to rough use it is not always a good idea. Ed Fowler uses "reverse" distal taper for this reason. On a short rough use knife no taper or even reverse taper is probably a good idea if you intend to wail on that knife. Distal taper looks good, and helps balance, but I would disagree that it makes a knife tougher in the context of this discussion. More flexible, yes. More likely for the tip to snap off, also yes.

Weight towards the tip increases the moment of inertia. Good on a chopper, bad on a fighter, annoying on a skinner or utility knife. So there are always compromises in a design.
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What exactly is a reverse taper I have heard about this before but I do not know exactly how it looks or is done.
 
chad2 said:
What exactly is a reverse taper I have heard about this before but I do not know exactly how it looks or is done.
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Distal taper is where the blade gets thinner towards the tip. Reverse distal taper is where it gets thicker towards the tip. It is not a common design element, but when done well it is both unusual and useful for certain kinds of knives. Typically forged, I don't think I've seen it in stock reduction knives except for a few art pieces.
 
If you are asking how to design a good knife, I think your first question should be: what will it be used for?
Design around that.
At work I use very thin knives with a 1" cutting edge. I wouldn´t want anything larger.
At home I use a 3,5" drop point knife and like it.
 
i am not asking how to make a good knife. i am asking what features you guys use or know of that make a good strong knife. this knife will be a medium sized knife about 6 1/2 inch blade will be used for general camp chores like chopping batoning and everything else. i am using 5160 so i already have a good strong material but i want to be able to push that material to its limits with out forging. my design will have all rounded edges, no holes, no jimping, and no extra material for a thumb ramp or finger choil.

this is a very rough design that i am still working on it has a drawn in finger choil which is how i would do it IF i did a g-10 handle but i am leaning more towards a paracord handle soaked in a flexable resin.

u3sz.jpg


the design creates a very heavy blade light handle and flexable incase of bad tree knots, or any other reason a knife might accidentally flex in hard use applications.

any advise on how to improve is very welcome. thanks for the help so far
 
No sharp transition areas as stress risers.
Thicker behind the edge.
Convex grind.
If you want something tough like an axe, think of how an axe is designed.
Just wait till you see the one I'm working on right now. :D
 
i want to do a convex grind but i am sacraficing ease of sharpening if i do so. i am going to be going a little thicker then usual behind the edge. and i am also thinking about rounding the bevel transition line. also i have a great axe but would like to have a knife that is good at everything but no perfect at anything.


show us! your design!

also i would love to see how people have made there designs stronger!
 
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chad2 said:
I am looking into more design features not steel types, that make a very useable and tough knife. What are some features that make a knife tougher design wise like all rounded edges, no jimping, distal taper, and drop point blade.

What are some other little features that help with toughness and make a knife more user friendly
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Fully hardened blade for full martensite to give max strength.
 
Look up some of Rick Marchand's work, and his posts on this and similar topics. What you have drawn up is very reminiscent of his work (flowing lines, no plunge, wrapped tang, no stress risers). That is unquestionably a good way to make the most of any steel's inherent toughness and resilience. Well, actually... I should say it's a good way to not take away from the steel's inherent properties... you can't really "make" a piece of steel any tougher. Straight out of the mill, it's as tough as it's ever going to get.

chad2 said:
the design creates a very heavy blade light handle and flexable incase of bad tree knots, or any other reason a knife might accidentally flex in hard use applications.
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Flexibility is dependent almost entirely on how thick the blade is, not its profile or hardness.

chad2 said:
i want to do a convex grind but i am sacraficing ease of sharpening if i do so.
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That's not a big problem. I routinely make blades with full-convex grinds, and put a small micro-bevel on the edge so they're easy to touch-up with flat stones or plates. Even as the blade wears down with lots of use, a properly-ground convex blade is really no more difficult to re-sharpen to a standard "V edge" than one with a full-flat grind.

Be wary of leaving too much thickness behind the edge, no matter what grind you decide on. Suit the knife to cut what you want, then choose steel that will support the type of edge you require.

Consider what I call a "compound grind", where the edge near the handle is thinner and bevel is flatter for slicing, but towards the tip the edge is thicker and the bevel more convex for chopping and batonning. This is similar to the reverse taper Nathan described earlier, and neither technique is as difficult as it sounds.

It's always going to involve some compromise, unless you want to build a super-tough heavy knife like Stacy described, which won't cut very well at all. (and many folks do just that).

chad2 said:
this knife will be a medium sized knife about 6 1/2 inch blade will be used for general camp chores like chopping batoning and everything else.
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You've already placed a great deal of restriction on what your knife will be able to do by choosing that "compromise" size range. A 6.5" will blade will never chop like a 9 or 10" one; there simply isn't enough leverage and tip speed. Nor will it ever be as nimble and handy as a 4" blade. I sell a lot of 5" survival/combat/utility/bushcraft blades, because, well, they sell. But personally I much prefer a thin 3-4" blade for almost everything, paired with a thicker, 9"+ blade for the heavy stuff.

Sorry for the long-winded post, but hey... you asked :)
 
James nailed it when he mentioned "compromise". If I want to build tough, I compromise cutting and slicing ability. Finding that sweet spot is the key. I have a model that has a 5" handle with a 6" blade. It is close to .300" thick at the spine. It will never win any cutting competitions and will probably destroy a perfectly good sushi roll... but it fits my ideal of a "survival" knife perfectly(for the moment). I named it the PIG... Purposefully Inflated Geometry.:p
 
Rick Marchand said:
James nailed it when he mentioned "compromise". If I want to build tough, I compromise cutting and slicing ability. Finding that sweet spot is the key. I have a model that has a 5" handle with a 6" blade. It is close to .300" thick at the spine. It will never win any cutting competitions and will probably destroy a perfectly good sushi roll... but it fits my ideal of a "survival" knife perfectly(for the moment). I named it the PIG... Purposefully Inflated Geometry.:p
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Any pics of the PIG Rick. I love your work and would love to see this one.
 
james terrio said:
Look up some of Rick Marchand's work, and his posts on this and similar topics. What you have drawn up is very reminiscent of his work (flowing lines, no plunge, wrapped tang, no stress risers). That is unquestionably a good way to make the most of any steel's inherent toughness and resilience. Well, actually... I should say it's a good way to not take away from the steel's inherent properties... you can't really "make" a piece of steel any tougher. Straight out of the mill, it's as tough as it's ever going to get.



Flexibility is dependent almost entirely on how thick the blade is, not its profile or hardness.



That's not a big problem. I routinely make blades with full-convex grinds, and put a small micro-bevel on the edge so they're easy to touch-up with flat stones or plates. Even as the blade wears down with lots of use, a properly-ground convex blade is really no more difficult to re-sharpen to a standard "V edge" than one with a full-flat grind.

Be wary of leaving too much thickness behind the edge, no matter what grind you decide on. Suit the knife to cut what you want, then choose steel that will support the type of edge you require.

Consider what I call a "compound grind", where the edge near the handle is thinner and bevel is flatter for slicing, but towards the tip the edge is thicker and the bevel more convex for chopping and batonning. This is similar to the reverse taper Nathan described earlier, and neither technique is as difficult as it sounds.

It's always going to involve some compromise, unless you want to build a super-tough heavy knife like Stacy described, which won't cut very well at all. (and many folks do just that).



You've already placed a great deal of restriction on what your knife will be able to do by choosing that "compromise" size range. A 6.5" will blade will never chop like a 9 or 10" one; there simply isn't enough leverage and tip speed. Nor will it ever be as nimble and handy as a 4" blade. I sell a lot of 5" survival/combat/utility/bushcraft blades, because, well, they sell. But personally I much prefer a thin 3-4" blade for almost everything, paired with a thicker, 9"+ blade for the heavy stuff.

Sorry for the long-winded post, but hey... you asked :)
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great thoughts there man deffinantly some stuff i need to consider thanks!
 
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