Heavy-duty backup knives: what kind of edge?

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Apr 29, 2002
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Hi, I'd like to know what everyone thinks about the type of edge a heavy duty backup knife should have. Specifically, what I have in mind is my Strider MFS.

I use it as a sort of heavy backup that will take the crazy jobs. Prying, hacking, stuff you wouldn't want to do with most folders. Perhaps self-defense, but in any case, my AFCK would be the first thing I'd reach for. I'm not a mall ninja, so it's not like self-defense is going to be a major factor in deciding the edge.

Basically, accuracy and cleanliness of cut are not too important to me. I don't get to use the MFS much, but I'd like it to be sharp and stay sharp in an emergency.

So with these kinds of requirements, would you put a rough edge or a polished edge on the knife? Is there much of a difference in edge-holding between these two types of edge?
 
I would go with a semi razor sharp edge vs. a thin and weak "shaving sharp" edge if I was chosing a soft tough steel like 420 J2. And I would go with a steeper angle edge for durability and strength for hard use. But if I was chosing something hard like CPM440V for a medium size blade, I would go with shaving sharp.

I'd recomend a Hibben Generation II Throwing Axe paired with a Kershaw serrated Boa in CPM440V for a survival combo. Use the axe to do chopping, digging an prying, and if a self defense situation arises you can put the thing to use for what it was made for and throw it! I don't think a rough edge (or chisle grind) has anything to offer over a polished edge other than it might be a little stronger and durable due to thickness. But that wouldn't be much of an issue if it was a harder steel like CPM440V. I haven't had good experience with 154CM Benchmades as far as edge retention goes. 154CM is difficult to sharpen and it isn't what I'd consider one of the harder steels.
 
isn't soft and tough together an oxymoron?
My experience with 420 is that it has to be thick for edge retention, and very thin for razor sharpness. You can't have it both ways.

As for a grind, anything will stay sharp if you don't use it, although for brute force and strength, a chisel grind is nice to have.

Identify what characteristics you need in the knife, then find a steel and grind that satisfy you. I agree that you should take an axe or tomahawk if you wanna chop.

here's another option... I've heard that this was done with cavalry sabers... that is to sharpen the first 1/3 of the blade to razor sharpness for delicate work and cutting while leaving a thicker chopping edge for the remaining (closest to the hilt) for brute strength.
 
Soft and Tough, as in not being brittle and hard. springy steel=strong steel. A titanium marshmallow would appear to be soft and tough as would a pad of steel wool. Or under inflated puncture resistant tires. Or puffy soft textured fire proof pray-on steel insulation.

Hard and Weak would be the brittle expensive steels and ceramic blades.

Damn that's a hard blade and it holds an edge better than anything I've even handled! :eek: Oops I dropped it and it shattered all over the floor. :(

A scary thought: Hard & Weak ceramic magazine springs. I think I'll use the soft & tough steel springs instead...
 
Hmm, maybe I should clarify, not that the previous replies haven't given me some useful information.

I'd just like to know what kind of edge would be the most durable, when the knife is used hard. Is the mirror-polished edge going to deform more than the rough micro-serrated edge when used to hack things? Or maybe the rough edge is going to chip more easily?

I ought to do some tests, though I don't have miles and miles of cardboard to hack through.

I'm sort of leaning towards putting a thick micro-serrated edge on the Strider MFS, since most of my other knives have a somewhat polished and thin edge.
 
Polished edges last longer.

If I were you, I'd see what roles my AFCK was playing, and make the Strider cover what your AFCK isn't covering. Sounds like you have already done this. Your thinned out, polished AFCK is your push cutting demon, so sharpen the MFS to a toothy edge. Use it for prying and hacking and slicing on tough materials, and use the AFCK for delicate point work and push cutting chores.

Cool combination of blades, by the way! I have an AFCK myself- awesome knife.
 
Tough in terms of edge retention... a tough knife retains it's edge... a marshmallow don't cut so well, do it?
 
A hard knife retains it's edge, a tough knife retains it's shape. ie not being brittle and shattering when it gets dropped on a hard surface.

I shave with a marshmallow every morning don't you?! :confused:

To me "tough" doesn't describe edge retention. It describe's strength and durability...
 
two valid definitions of tough with two very different meanings...

What about a chocolate bar... hard and brittle (when cold), but not very sharp.
 
Chocolate isn't steel. Chocolate wouldn't be described with the same definitions as steel. But it works for describing some things like steel wool, wire mesh, shark suits, etc... Soft, tough and hard would decribe a steel or titanium shark suit. Because most people don't consider 'sharpness' or "edge retention" when they're shopping for a shark suit. Nor do they consider those when shopping for chocolate.

The only sharp food I know of is cheese.
 
what about sh*t?
I constantly hear about tough sh*t, but all the sh*t I encounter is kinda soft and mushy...

what's your take on tough sh*t?
 
LOL. You semantics hard asses. Mmm... marshmallows and chocolate. S'mores, kinda crisp on the outside but nice and soft on the inside... like a TiNi coated blade...

Thanks for the information. I'm going to put a rough edge on the MFS because it *might* come in handy if my polished AFCK is slipping while trying to cut. It doesn't really matter how long the edge lasts, since it's not like I have to stab car doors all the time. :) And even then, all it takes is a nice strong tip.
 
Originally posted by MelancholyMutt
what about sh*t?
I constantly hear about tough sh*t, but all the sh*t I encounter is kinda soft and mushy...

what's your take on tough sh*t?

If you ate shaving sharp chocolate all the time, you would probably experience some sharp pains in the bowel region. :D
 
Polished edge is more durable.

Edge thickness and angle have exactly zero to do with sharpness.
 
When you say "backup", what is the primary tool that you will be backing up - knife, shovel, prybar, entrenching tool? "Backup" implies that this will come into play only when the "primary" has failed. And you talk about "hacking", then talk about cardboard. True, cardboard is tough on edges, but when I hear "hacking", I'm thinking of making a campfire or a survival snare, or escaping a burning building. I guess I don't understand the intended use.
 
Backup to me means a desperate situation, which could include self-defense, short-term survival or escape from an enclosure, such as, in my case, a crashed helicopter.

I carry a Spyderco Native as my EDC.
It does all kinds of things for me; neatly, conveniently, and with a socially acceptable appearance.

I back it up with a Greco Persian in A2.
I carry the Persian in a slip sheath in the front pocket of my Levi Dockers, or in the tool pocket on the right thigh/hip of my overalls.

A close associate from my New Orleans days, who knows too much about these things, told me that a "self-defense" knife should have the ability to hit a belt buckle and still retain its edge.
I made that my top priority, along with concealability, in my selection of my backup "desperation" knife.

John Greco heat treats his knives dead soft in the spine and hard as he can and still retain a high charpy index at the edge.

John Greco gave my .25" thick A2 Persian a mild hollow grind, which still leaves it with a substantially thick edge - probably too thick for most people's ideas of a general purpose knife.
The knife came from John plenty sharp, but I beveled the edge at sevral angles and then burnished the flats and ridges of the angles into a continuous curve using a good quality straightening steel.
This gave the blade a thick convex edge that anyone can see with the naked eye.

I tested this edge on an aged hickory axe handle, whittling at all angles, prying and twisting, and generally tired myself out.
The edge would still shave hair and effortlessly cut printer paper.
I have seen pictures of this knife punched through the roof of a full-sized American car and still shave hair and cut paper.

One interesting thing about this knife: when dropped on a hard surface it rings like a cathedral bell.
I have read from one source that this doesn't mean anything, but it sounds so cool.

Anyway, I consider this the most knife in the smallest package I have yet encountered.
It seems indestructible to me and it holds a razor edge against all materials I have cut with it.
It would certainly come away from a belt buckle undamaged.

For a long-term survival knife I would prefer a stainless steel, but different materials for different jobs.
 
Originally posted by OwenM
Polished edge is more durable.

Edge thickness and angle have exactly zero to do with sharpness.

Hmmm, I take it then the sole factor in sharpness is the edge being well aligned, i.e. the edges meet at the same angle, with no burrs or wire edges, flat spots that sort of thing???

This is the first time I have seen sharpness seperated from cutting ability (in which edge angle and thickness have a tremendous impact.) It is a very interesting point, and one that shows solid understanding of how a knife functions.

That kind of precision of thought is rare, but coming from you own it is not suprising.

Take care and stop by the other place sometime, we miss ya!
 
Originally posted by RH
When you say "backup", what is the primary tool that you will be backing up - knife, shovel, prybar, entrenching tool? "Backup" implies that this will come into play only when the "primary" has failed. And you talk about "hacking", then talk about cardboard. True, cardboard is tough on edges, but when I hear "hacking", I'm thinking of making a campfire or a survival snare, or escaping a burning building. I guess I don't understand the intended use.
I admit that a "backup" can be a backup for many things. But I intended that the MFS would be a backup primarily to my AFCK. So in a situation where the AFCK would not suffice or has failed, I would then use the MFS. This includes prying tasks.

I've got pretty much the same stuff in mind regarding "hacking". However, in the course of living my urban apartment life, I don't get to make many campfires. :) So the cardboard would be a way to test the durability of the edge.

So, to sort of summarize what's gone on in this thread:
As is often the case, the answers to my question aren't absolute. I've got to find a suitable tradeoff between the durability of a polished edge, and the utility of an edge type complementary to that of my AFCK.

The side discussion on the (non)relationship between sharpness and edge angle/thickness is also an interesting point. Here's what I understand from reading the forums:

If you're measuring pure sharpness, a test would be something like the ability to cut a free-hanging hair. But when the task involves anything else, the "sharpness" or perhaps more accurately "cutting ability" is also affected by the material to be cut and the edge angle.
 
AlphalphaPB,
Basically for “crazy jobs” as you and Ken have mentioned any folding knife is not suitable, IMO. Such knife should be some kind of compromise between sharpened prybar and still adequately good cutter – the properties what are pretty hard to reconcile in the single piece.
I think it should be pretty small and relatively thick fixed blade with convex edge for additional strength. Something like Fallkniven H1 although it is intended for completely another purposes.
H1_02.jpg

Also, I would polish the edge as high as I could for additional durability when cutting.
There are some tricks how to use even so small (but hefty) knife relatively efficiently for light chopping, I just should make some additional photos to explain this.
 
Originally posted by Eric_Draven
Hmmm, I take it then the sole factor in sharpness is the edge being well aligned, i.e. the edges meet at the same angle, with no burrs or wire edges, flat spots that sort of thing???

This is the first time I have seen sharpness seperated from cutting ability (in which edge angle and thickness have a tremendous impact.)

Well, that's how I think of sharpness:)
Guess I could have qualified that statement by adding "...but everything to do with cutting ability" to the end. You can get a thick edge just as sharp as a thin one, but that doesn't mean it will cut well.
Realizing that the edge bevel's angle doesn't reflect its thickness really screwed up the results of some of my little "tests", too, and has had me playing with back bevels for awhile now (told you about trying multiple bevels on my Basic 9).
Example: Last night I helped my best friend install a new water heater after work. It came in a very sturdy box, which I used 3 different knives to cut up, out of curiosity-a 1/4" Busse Basic 4, a 1/8" CF ArcLite, and a 1/16" blade on an Old Timer stockman. All had edges sharpened at 40 degrees included and with same level of polish, but naturally there was a HUGE difference in cutting ability, with the two thinner blades having a tremendous advantage since the material was both thick and binding. The ArcLite's hollow ground recurve allows it to cut on par with the blade half its thickness. Add blade shape, and geometry to the mix, and we've got a neverending discussion on what makes a blade "work".
Man, I love this stuff:D

I can see why makers and guys like Cliff measure the thickness of the edge and say "it's .030 behind the edge", instead of just giving the edge angle.
 
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