Couple edge damage pics

[Cliff Stamp]

I really like the cutting performance offered by the thin & narrow angled edge.

Since the damage is constrained to a small fraction of the edge bevel the entire edge bevel doesn't need to be made more obtuse. A decent starting point is to grind the edge at the existing angle until the damage has been cut in half at the deepest point and then increase the bevel a few degrees to remove the remaining damage. Since this additional bevel is only a small fraction of the main bevel width it should have a corrospondingly small reduction in the cutting ability but can still induce a large change in the durability. It also only has to be done in the spots where you are likely to use for heavy impacts.

As I've mentioned before, the reason I'd do this is to discover what happens when things aren't precisely controlled, as my more "serious" useage is rather dynamic.

All actual use tends to be which is why I have critized a lot of the pseudo-static cutting that a lot of makers use to promote their knives because it leads to highly artificial results. When you are cutting a raccoon for example, or any other animal, both it and you are likely to be moving and all the contacts are going to be highly dynamic and would in no way be represented by hanging a bone and doing a perfectly smooth cut through it.

A while back in Blade, one of the competition cutter guys said he sharpens his comp knife with an edge much finer and sharper than what he'd ever give to a customer. That alone should tell him the competition tests no longer represent real world use.

It should be obvious because the cutting is very light and the volume very low, it is mainly an exhibition of speed and precision. I'd rather the approach that Fikes takes in his video where he does a bunch of such really controlled cutting and then goes in the woods and just whack apart a bunch of wood, chops into a steel drum and pounds a knife through a concrete block.

I had considered S5 & S7, but was put off by reports of plastic deformation even at moderately high hardness.

Hardness measures resistance to deformation, in general if you are seeing deformation failure you can't solve this problem by moving to another steel, you have to increase the hardness. I'd suspect improper heat treating and/or improperly calibrated Rockwell testors.

"Changing grades will not help a deformation problem unless the new grade is capable of a higher hardness."

That is a direct quote from Crucible steel, the same would be found in any tool steel book and even in the steel patents. What I have heard with S7 from some of the makers who are using it is that it is very hard to actually get it to 58 HRC even with a oil quench and cold so it may simply be that some are actually using steel softer than they think. You may want to check with the steel supplier and confirm the composition and tolerances that they are using for the steel.

-Cliff

 

[JurT]

JurT-
I've written about this bowie lots if you care to do some searching. Basic description here.

Thnx for the link. It's a realy nice bowie.:thumbup:

 

[Rat Finkenstein]

Here are the pics (bad ones) of the damage and the edge thickness.
Damage is less bad than I thought, and there is no sign of damage from the portion of the edge I used to chop the banding. The nicked spots are from the first cut using improper technique.

 

[the possum]

possum, Cliff makes a good point about the angle you chop the bone.

Thanks for chiming in Scott. I'll have to keep that in mind when we're doing some more butchering later. I'll try a couple different approaches with my old F. Dick cleaver & see what happens. At the same time, as I mentioned, I want to know what happens in dynamic use as well.

Ron Hood does indeed still use the frozen elk leg test on knives he evaluates. He used the Buffalo knife I sent him on a frozen elk leg and it is documented in the Woodsmasters series vol.17. The knife I made was 3/16" thick D2 steel with an 8" blade. Full convex grind and edge. He shaved hair off his arm afterwards.

So do you attribute this to his chopping technique? 'Cause I'm not seeing how D2 could take less damage on chopping hard stuff than 5160 bainite, unless your edge is like twice as thick. And I don't like thick edges.
Alternately, as I've mentioned, the bar of steel I used to make this knife has some problems, so maybe once I actually start using a knife made from good steel I'll see what I was missing.

 

[the possum]

Since the damage is constrained to a small fraction of the edge bevel the entire edge bevel doesn't need to be made more obtuse. A decent starting point is to grind the edge at the existing angle until the damage has been cut in half at the deepest point and then increase the bevel a few degrees to remove the remaining damage. Since this additional bevel is only a small fraction of the main bevel width it should have a corrospondingly small reduction in the cutting ability but can still induce a large change in the durability. It also only has to be done in the spots where you are likely to use for heavy impacts.

Off hand, I can't put my finger on it, but my gut reaction is that increasing the edge angle much more, even on just a narrow width of the edge bevel, would decrease my cutting ability more than I like. It's been a while since I've really compared it though. Since I'm using a very coarse edge for draw cutting, the micro teeth may be shorter or something. But there have been times in the past when I used a microbevel up to 30 degrees per side (mostly when the coons discover the silo at the quonset- then most of my cuts will be on concrete) but I generally don't go that high now. I can't point to a specific instance where I noticed a problem with this steeper edge, but over time I've come to like the shallower angle.

I do use a steeper angle on the last 3 inches of the tip for this reason though. I found that since I made the knife, it has lost 1/4" of length, but only 1/8" of width, indicating the tip area sees more abuse and therefore needs beefing up more than the belly.

I probably would do this (roll on a steeper bevel at the very edge) if this level of damage really bothered me. But really, if I can sharpen it out in 5 or 10 minutes, it ain't a huge deal. Like I said in my first post, I was posting these pictures more to share for discussion rather than in disgust. Sure, I'd like better, which is why I'm exploring other materials, but the edge I'm using now has no trouble with my primary targets. It's always those accidental impacts on hard stuff that cause the problems, but I can't let them totally dictate things either.

What I have heard with S7 from some of the makers who are using it is that it is very hard to actually get it to 58 HRC even with a oil quench and cold so it may simply be that some are actually using steel softer than they think. You may want to check with the steel supplier and confirm the composition and tolerances that they are using for the steel.

If only I didn't spend so much time surfin' the web, I might actually be able to accomplish more of these projects. I haven't discounted the shock steels, and am still wanting to try them. It just may be a year or two.

 

[the possum]

Rat-
thanks for the pictures. That edge certainly does look thinner than the ones I saw at the show, but it's still kinda hard to tell from pictures like this when thousandths of an inch can make such a big difference. Really it doesn't look bad at all though.

A trick I've found useful for measuring edge thickness is to press the edge into a piece of wax. Press it until the wax extends halfway up the edge bevel, and make another impression to the full depth of the edge bevel to get an idea of the geometry. Then you can compare the width of the notches left in the wax to something of known thickness if you don't have a calipers. I've always got mechanical drafting pencils layin' around that take leads .5 and .3 mm thick to compare with.

 

[Gossman Knives]

possum, angle of the chop has alot to do with it. Ron chopped the elk leg at an angle. He also used Bill Siegles Hoodlum II on the elk leg chop with no edge damage and Bill uses 5160. It very well could be the steel you used. I don't have thick edges on my knives but they are convexed which I believe are stronger.
I've worked with S7 as you know and it can't be hardened higher then 59. If you go to 59 impact resistance drops. The edge on my S7 blades will roll before they chip. Mine are at about 57.
Scott

 

[Cliff Stamp]

Since I'm using a very coarse edge for draw cutting, the micro teeth may be shorter or something.

They are, you will need to go more coarse to get the same level of aggression at a higher angle.

Scott the edges of your knives are extremely think and obtuse unless you have changed them significantly since you last posted work you had done with one of your D2 knives. Your edge on a medium sized utility knife was much heavier in cross section than even a splitting axe. With those types of profiles it isn't surprising that the durability is high which is why you need to note the cross section when making an inferences about durability.

-Cliff

 

[Gossman Knives]

They are, you will need to go more coarse to get the same level of aggression at a higher angle.

Scott the edges of your knives are extremely think and obtuse unless you have changed them significantly since you last posted work you had done with one of your D2 knives. Your edge on a medium sized utility knife was much heavier in cross section than even a splitting axe. With those types of profiles it isn't surprising that the durability is high which is why you need to note the cross section when making an inferences about durability.

-Cliff

Yes they are according to what you consider thick and thin. The thickness that you like would never withstand heavy work. possum I'm done here because as usual Cliff wants to argue again. If you want to discuss this anymore email me. Good luck with your knifemaking. I should have known better then to post here.
Scott

 

[Cliff Stamp]

Yes they are according to what you consider thick and thin.

This is the part you leave out when you talk about the durability of your edges.

"At a 1/16" back it's 0.075 at 1/8" back it's 0.108"

The edge is ground over 30 degrees per side. The fact that it is durable has nothing to do with it being convex. It is simply extremely thick and obtuse.

The thickness that you like would never withstand heavy work.

That is kind of funny, now I get accused of not using my knives heavy enough.

-Cliff

 

[the possum]

Scott, c'mon man. I know Cliff's people skills could use some work, but there's no reason to tuck tail & run here. I ain't trying to be confrontational. If he bothers you, just ignore him; don't give up on the conversation.

Now then, I must agree with him that you confirmed my suspicion about the edge thickness.

"At a 1/16" back it's 0.075 at 1/8" back it's 0.108"

I gotta say, Holy Crap, Dude! That edge is more than twice as thick as what I'm using. At 1/16" back, my edge is .031", and it's .043 at 1/8". If I set the calipers at .108", they slide nearly 3/4" up onto the main grind.
You seem to think this thickness "would not withstand heavy work". For the record, in the past, you gave me a bit of guff for using my blade too hard. And even Cliff thinks I run my edge a little on the thin side. This is an 18" blade that can generate lots more speed and power than any 8" utility knife, and it can snick through a 2" hardwood branch in one swipe (cherry & ash), cleave a raccoon in half with ease, & chop big wood better than my old khukri. It can easily handle all these tasks with zero damage. The only problems come when I accidentally whack concrete or something, and even then it just needs 10 minutes on the stones to fix; it's not seriously damaged up into the main grind.

I ain't trying to piss you off here. I just want to illustrate where I'm coming from. This is the kind of edge I want. I can certainly see where you'd need a thicker edge on a D2 blade, but is this the same edge geometry you use on your S7 knives? I should think you'd be able to take them half as thick for better cutting performance & still be able to take plenty of genuine abuse. I'd be very interested to know this since I'd like to try S7, at the edge geometry I listed above. Maybe we just have a different philosophy on this- is your main goal to prevent any sort of edge damage at any cost? I am willing to accept the nicks now and then to get the better cutting performance.

 

[Gossman Knives]

possum, for the record I don't tuck tail and run. I'm very busy and can't hang on the computer as much as I used to. Cliff and I will probably never agree. Now this really is all pretty much common sense. If you are going to do heavy work, the thinness you like isn't going to hold up. Yes I do run my edges thicker then your bowie but they are not so thick that the knife can't be used for finer work. I've got several hundred knives out there and have never had one come back because it was too thick. I've had people do everything from split wood, chop and then carve a spoon and that's with a camp knife. I get factory knives sent to me all the time to redo the edges because they were too thick. I've talked to Ron Hood and he told me he has a box full of broken hollow ground blades. He prefers flat or convex grinds. I talk to my customers about what they plan on using their knife for. If it's strickly for camp kitchen, slicing or really fine work, I recommend going with thinner stock. I can and have ground edges down to a zero edge, very thin. I just don't prefer to do that. I don't get into measuring what the edges are. After making as many knives as I have I know where they are at just by looking at them. The best way is to take them out and test them. If you run S7 as thin as you like it will roll. You can't harden it high enough for it to chip out. The only way I can see it chipping is if it wasn't tempered properly.
Scott

 

[Cliff Stamp]

I should think you'd be able to take them half as thick for better cutting performance & still be able to take plenty of genuine abuse.

You don't need close to half, even on 50100-B, which isn't an overly tough steel, it is extremely difficult to induce fracture deeper than 0.025" and that steel will chip readily on hard contacts. I took a CU/7 and chopped it into nails half way driven into a 4x4 and I still could not get the damage to deepen past 0.025".

Stiffness is cubic in thickness so you see massive gains fast. About 0.015" is fairly difficult to chop wood with and not have it ripple because it bends so easily under the lateral loads however moving up to 0.030" makes the edge about ten times stiffer and it becomes so durable you can pound it through thick knots in heavy rounds with a framing hammer and the edge will not ripple.

That heavy metal cutting was done with a Howling Rat and even pounding on the knife with a hammer through thick metals just blunted the edge back to about 0.030". The knife eventually broke directly basically in half through the impacts but assuming the steel would not chip there would be no need to have it thicker because you are not going to actually ripple it.

Similar gains are seen with angles for the same reason. I find about 10-12 degrees is functional for wood chopping (up to a small parang, 14") as long as I am careful and the wood doesn't snap or twist, however at about 13-15 I can hack dead limbs off standing trees with no regard to technique and no damage to the blade. It doesn't seem like a lot but if you look at the percentages and then triple them it makes a big difference.

Busse is using S7 in their new fixed blade line (Scrap Yard) and he is usually very willing to talk about edge geometries so just call/email him. He will get very specific about angle/thickness if you ask. Thom also has a S7 bowie which he has reground and subjected to fairly harsh work, metal chopping and the like. S5 offers a slightly higher hardness and would be a better steel for larger knives but you may have a problem getting it in bar stock. There are also a bunch of P/M shock steels which go up to 62 HRC but are much more expensive and generally only useful if you also want the wear resistance - or just have the money to spare. You can probably get samples if you ask.

There are also a bunch of guys on Swordforums who would likely do a bainite blade for you just for evaluation purposes. I have been offered heat treating services when just discussing potential configurations.

-Cliff

 

[the possum]

possum, for the record I don't tuck tail and run.

Ha! I knew I could get you back in here with a little prodding.

If you are going to do heavy work, the thinness you like isn't going to hold up.

Scott, we seem to be having a serious misunderstanding here. I've broken a bunch of knives in my day too. I have used this knife for what I consider to be very heavy work, and it has held up just fine. Prying would not be one of its strong suits, but serious impact on chopping is. But since we're mainly talking about edge damage in this thread, I'm not sure what kind of heavier work you're even talking about.

I've got several hundred knives out there and have never had one come back because it was too thick.

You obviously have no need to change things if you're keeping your customers happy. I'm just pointing out that my preferances may be different from your average customer.

I don't get into measuring what the edges are. After making as many knives as I have I know where they are at just by looking at them.

Yeah, I feel the same way. I only started taking measurements since joing bladeforums, since it's so hard to convey what I'm talking about otherwise. We've already seen the result of differing definitions of thick or thin right here. The numbers make it easier to imagine something that's very hard to tell from a picture, or just from a description. This leads me to my next question-

If you run S7 as thin as you like it will roll.

How bad of a roll are we talking about here? (this is where some numbers would help.) I can live with rolling that can be easily fixed on a few swipes with a stone. But if you mean I'd get ripples extending up into the main grind, well, I'd be less enthusiastic about trying this steel.

 

[Gossman Knives]

I know you've seen this blade that was shot so I don't think rippling would be a problem. The very edge would roll, especially if it's a secondary bevel. The point on that blade also bent a little when I checked the point strength. It didn't break off like harder knives would have. The heavier work would be batoning with hard lateral force and heavy chopping where the edge might hit a hard knot. You have to remember with a convex grind it is naturally going to be thicker along the main grind but with the rotary platen I'm using, my grinds are less convexed. Tighten the belt on the platen enough and you can flat grind.
Scott

 

[the possum]

Stiffness is cubic in thickness so you see massive gains fast. About 0.015" ... it bends so easily under the lateral loads, however moving up to 0.030" makes the edge about ten times stiffer....

I find about 10-12 degrees is functional for wood chopping as long as I am careful and the wood doesn't snap or twist, however at about 13-15 I can hack dead limbs off standing trees with no regard to technique and no damage to the blade. It doesn't seem like a lot but if you look at the percentages and then triple them it makes a big difference.

Triple them, or cube them?

I am still impressed by that blade, Scott. I haven't shot any of mine yet, 'cause I don't have time to make a replacement now.

If you are going to do heavy work, the thinness you like isn't going to hold up... The heavier work would be batoning with hard lateral force and heavy chopping where the edge might hit a hard knot.

I haven't done any heavy batoning on my bowie since it's double edged. (That, and because why the heck would I need a baton with an 18" blade? )

However, the second part of your statement makes it clear we just have different preferances and are talking around each other here. You've seen what happens to my blade when chopping deer leg bones, concrete, rocks, scrap steel, glass, teeth, and other very hard substances much tougher than a stinkin' knot. And those impacts are hitting with way more power than any 8" blade could. Yet, all I get are some nicks that don't even go halfway up the edge bevel. We are not talking about breaking the blade in half or blowing big chunks out of the main grind here. I could easily reduce that damage to practically nil if I wanted to sharpen the edge steeper.

Obviously this level of damage is unacceptable to you. And that's fine. You wouldn't hurt my feelings by saying so.

Either that, or you're saying that what I have been doing for years is impossible.

 

[Cliff Stamp]

The heavier work would be batoning with hard lateral force and heavy chopping where the edge might hit a hard knot.

How many high quality blades have you damaged in such use to support such an arguement. Are you honestly saying that the knives from Swamp Rat which have edge profiles for their large knives at about half of what you used on that small knife in both thickness and angle are unsuitable for batoning or heavy chopping?

I've talked to Ron Hood and he told me he has a box full of broken hollow ground blades. He prefers flat or convex grinds.

Ron promoted and sold hollow ground blade for years and still speaks well of them, the TOP's Anaconda for example.

Triple them, or cube them?

Multiplying percentages is an approximation, a ten percent increase of something which has a cubic influence produces roughly a 30% increase. The exact increase is 1.1^3= or 33%. Generally you are not precise enough in changes or even the dependancy of the influence to make the approximation variance significant. This approximation is based on the fact that (1+x)^n = 1*nx if x is small.

You've seen what happens to my blade when chopping deer leg bones, concrete, rocks, scrap steel, glass, teeth, and other very hard substances much tougher than a stinkin' knot.

When you baton the concern isn't hitting the knot, it is when you are in the middle of the knot during the cutting. Unless you keep the blade and the impact are perfectly aligned as is the blade/wood orientation, there will likely be a load across the edge. Imagine chopping your bowie into a piece of bone which makes a partial cut and now slamming a piece of wood 90 degrees into the spine to basically lever the bowie out of the bone sideways. That is the worst case senario for worse case knot cutting. You can of course just reduce the impact energies of the swings to match the strength of the blade and prevent damage. I have chisel cut 3.5" nails with Deerhunters with no damage.

However even in the cases where you just let fly at full force, it is extremely difficult to actually turn an edge which is even 0.030" thick. I spent hours last year trying to do it with a couple of knives which were under that with no success and I was hitting the blades so hard I had to pad the handles because the impact shock made it impossible to hold on the blades. I don't mean it was uncomfortable, I mean I was concerned about my hand breaking. I calibrated the level of impact energies and they were significantly greater than my brother using a 28 oz framing hammer and he is a carpenter and swings a mean hammer.

Again, considering that strength and stiffness are quadratic and cubic in thickness, it doesn't take much gains before you simply outside the ability of a man to generate the force. An edge which is just 0.075" thick for example is 10 times as strong and 30 times as stiff as an edge which is 0.025" thick. Even the strongest, heavily roided individuals on the planet are only about 2-3 times as strong as a physically active man.

-Cliff

 

[auto veritas]

this may be a slightly back handed comment but in all truth ... someday i hope to have enough knowledge to converse on the same level with you weirdos while speaking of knives

 

[the possum]

When you baton the concern isn't hitting the knot, it is when you are in the middle of the knot during the cutting. Unless you keep the blade and the impact are perfectly aligned as is the blade/wood orientation, there will likely be a load across the edge. Imagine chopping your bowie into a piece of bone which makes a partial cut and now slamming a piece of wood 90 degrees into the spine to basically lever the bowie out of the bone sideways.

Though I don't have much experience with batoning, this sounds very similar to the forces the edge would see in dynamic chopping. When the target is not anchored solidly, it will move/twist as the blade is cutting through it. The leg bones spin and pull my blade out of line, and it's happened several times while cutting hardwood saplings that the blade gets about halfway through, and the tree bends, practically twisting the knife out of my grip and popping the blade back out in the process. Pure sideways torsion on the edge.

The only difference is that the edge is hitting with the force of a swung 28oz bar of steel, rather than a 28oz baton. I can see that on smaller knives that don't have significant chopping power, the added force of the baton would be more decisive.

 

[Cliff Stamp]

The only difference is that the edge is hitting with the force of a swung 28oz bar of steel, rather than a 28oz baton. I can see that on smaller knives that don't have significant chopping power, the added force of the baton would be more decisive.

Yes, I keep forgetting the size of the knife you are using, your bowie has impact energies similar in class to general spine impacts. It would be fairly easy to check, just chop with the bowie into a piece of wood a few times, 90 degrees, to benchmark the penetration and then place the edge into the wood and smack on the spine and check the depth. Like you noted, if you do this with a 7-10" blade you can usually get far greater penetration with impacts because you can swing a stick which is several lbs. But considering your bowie is personally optomized for speed/power it may in fact be far more powerful than a randomally selected piece of wood.

The big concern from a general perspective is user skill/method. When I sharpen knives for other people I sometimes leave them a little thicker because they will see much wider use and for most people, minimizing damage is more important than optomizing cutting ability. So for example if I run 8:0.015"/14 on a personal chopping blade I could go up to 10:0.020"/16 for a more general blade to handle abusive limbing and knot chisel cutting and 12:0.030"/18 for a "survival" edge with a 0.1 mm wide 25 degree micro bevel. This is pretty much invunerable, you can hack and baton through knots with no concern so it works well for someone who is inexperienced or is experienced but is highly stressed.

This assumes of course a sensible tool steel which is tough and very hard. On the softer machetes and more brittle steels you have to thicken them to prevent roll/fracture respectively. But again since strength and stiffness are so strongly above linear it doesn't take much of a change in cross section. Just consider the effect that spine thickness has on strength. A 10" blade which is 3/16" is very "floppy" and easy to bend, but a 1/4" blade is extremely difficult to bend as it is actually 2.5 times as stiff. It is why 1/2" thick spines would be absurd because they would be 20 times more rigid. The edge of course has the same behavior so you think of changes of the same scale. Because the edge is so thin it only takes small changes to induce large percentile differences and the percentages are what you are interested in as they determine the relative performance.

This is also why you measure the edge, just like you noted for balance awhile ago when Thom commented about how many makers go by feel. Once you start measuring the balance you can refine design much faster and of course it allows more definate communication. So when a maker tells me a large brush blade has static and dynamic balance points very close together and right at the handle then I know what this means (the blade sucks) if he just says "It balances well, great feel." I don't know anything. The edge is no different. If someone highly praises a steel for toughness and notes the edge is 30 degrees per side and 1/8" thick well then I am not going to be overly impressed because anything will be durable with that profile and the cutting ability is going to be poor. That quite frankly is why many shy away from measurements because facts prevent hype.

-Cliff