Hard Use and The Durability Of Various Edge Angles

[Vivi]

Ever since being introduced to reprofiling my knives by Cliff Stamp I've maintained that knives should be ground thin as long as they're being used by responsible people who understand how to properly use a knife.

Currently we see knives shipping from prominent manufacturers with edges thicker than many factory axes come with. While I disagree with their methodology, it's understandable in a sense considering what the "average" consumer would expect of their knives. However I still think leaving the edge irrationally thick has serious drawbacks, such as giving people the impression that the way X knife cuts from factory with a 40 degree inclusive edge is the way a knife should cut. It also gives people the idea that a knife is to be used forthings it shouldn't be. 3 inch bladed pocket knives make terrible pry bars and metal cutters, there are much better tools for the job. Small knives excel at cutting up food, slicing cardboard etc. Sure, you can design a knife that will be able to pry and be hammered through nails, but it will still be worse than a use designed tool, it will be terrible at common knife jobs and will cost more. I don't know anyone that regularly batons their folders for firewood or stabs through car hoods. The only time I would consider a 40 degree inclusive edge is if I were planning to use a knife solely for chopping through metal. Even my kuhkuris and large chopping axes are thinner than that at the edge, so why are pocket knives with 3 inch blades being kept this way by people knowledgeable enough about knives to sharpen them?

The thin edge has many benefits. If one utilizes microbevels it will decrease sharpening time tremendously. There are obvious benefits in the amount of force need to cut through media due to the thinner geometry, which results in less fatigue for the user and less stress put on the parts of a knife. It has been observed that there could be an increase in edge holding as well, though I have not tested this personally so will not claim it as fact.

I want to know what things you are doing with your pocket knife that makes you desire a 30 degree inclusive edge or greater. I want to know whether or not you've tried taking it down to 10 degrees per side, and if you have, why it wasn't strong enough for you.


In this video the Byrd Cara Cara I have posted for a pass around did light chopping ad was stabbed into a can of corn. The edge handled this fine.

http://www.youtube.com/watch?v=IMpS-pKQlzI

http://www.youtube.com/watch?v=zW8bc7W3Qik
http://www.youtube.com/watch?v=1SFG9-6Bmp0

Here are threads with photos of each knife: http://www.bladeforums.com/forums/showpost.php?p=5270406&postcount=1
http://www.bladeforums.com/forums/showpost.php?p=5487840&postcount=339

Note, the UKPK is ground even thinner since the photos were taken.


I've read the "What do you cut with your knives" threads and this use is not typical of the majority of users knife usage. It's much harsher. So why is it so rare to see knives ground at 10 degrees per side or less discuss here or posted in photo threads, when as I just demonstrated, they are more durable than what most people here have stated they need?

Taking this further, I do not understand why saber grinds are so popular.

Why pay for the latest super stainless steel and not even give it an edge to show it's true nature? Especially considering these high RC steels can take terribly thin edges.

I'm trying to understand the rational basis for these types of edges but so far have failed to find one?

If you re not convinced, send me a knife and I will regrind it for you myself at no charge so you can see what I'm talking about. (Certain conditions apply, e.g. I won't do recurves, one knife per member etc.)

 

[me2]

Regarding saber grinds, IMO it has to do with steel removal and appearance. Some knives just wouldnt look right with full height flat grinds or convex grinds, and saber grinding reduces the amount of steel that has to be removed, therefore reducing manufacturing cost. Consider the scandinavian grinds and machetes.

Regarding lower edge angles, many knowledgable people will reduce the bevels on their knives. My kitchen knives are between 12 and 16 degrees, with microbevels between 15 and 20, because I like the Sharpmaker for weekly touch ups and those are its angles. My work knives are in the 20-25 degree range because I occasionally need to cut metal.

Also consider that most people only carry one knife. That knife must do all the things they need a knife for without breaking or chipping. I really like the multi-bladed traditional pocket knives for verstility. I carry a trapper with the clip blade ground and honed at about 15 degrees, while the spey blade is at about 23 degrees, now with a 60 degree inclusive micro-bevel, made using the opposite stone on the Sharpmaker as an angle guide, then moving to sharpen the opposite side, using the 30 degree inclusive slots. The spey gets used for deburring conduit, scraping, and rough jobs.

Durability in cutting is not the only consideration. Take a RADA cutlery santoku down to 24 degrees inclusive and cut with it and you'll be pleasantly surprised. Run it through the dishwasher and you'll be jumping up and down from the nicks that have to be repaired.

 

[oli]

.....I've maintained that knives should be ground thin as long as they're being used by responsible people who understand how to properly use a knife.

...... However I still think leaving the edge irrationally thick has serious drawbacks,.......
The thin edge has many benefits. .... There are obvious benefits in the amount of force need to cut through media due to the thinner geometry, which results in less fatigue for the user and less stress put on the parts of a knife. ........

Why pay for the latest super stainless steel and not even give it an edge to show it's true nature? Especially considering these high RC steels can take terribly thin edges.

Why stop at the edge? Why not make all knives as thin as a paring knife? And get rid of all of your leaf shaped blades because it is just causing additional friction requiring more force while cutting through media. We are talking about cardboard here, right?

 

[Vivi]

I'd personally love seeing more blades ground from 2mm stock or thinner. I wish the UKPK was thinner than 3mm.

Regarding saber grinds, IMO it has to do with steel removal and appearance. Some knives just wouldnt look right with full height flat grinds or convex grinds, and saber grinding reduces the amount of steel that has to be removed, therefore reducing manufacturing cost. Consider the scandinavian grinds and machetes.

My post is geared more to purchasers than manufacturers. If someone intends to do a lot of prying with their knife, despite there being better tools for the job, then a saber grind would make sense. But forpeeling an apple, whittling wood or slicing cardboard, it only hinders cutting ability. What does the average Bladeforums poster do with their knife moe often, heavy prying or light cutting? The threads about what we use our knives on suggest the latter.

Regarding lower edge angles, many knowledgable people will reduce the bevels on their knives. My kitchen knives are between 12 and 16 degrees, with microbevels between 15 and 20, because I like the Sharpmaker for weekly touch ups and those are its angles. My work knives are in the 20-25 degree range because I occasionally need to cut metal.

If you have any information regarding how different steels and edge variations have worked for you while cutting metal, and what exactly you cut while doing this, I would love to hear it. I don't do any of this on a regular basis, my metal cutting has been for durability testing only for the most part. Based on my limited experience I would think a 12 degree per side secondary bevel with a microbevel at 16 or so would hold up the most metal cutting I would expect of any small knife. Have you tried anything around this range and hd it not perform as you'd like?

Also consider that most people only carry one knife. That knife must do all the things they need a knife for without breaking or chipping. I really like the multi-bladed traditional pocket knives for verstility. I carry a trapper with the clip blade ground and honed at about 15 degrees, while the spey blade is at about 23 degrees, now with a 60 degree inclusive micro-bevel, made using the opposite stone on the Sharpmaker as an angle guide, then moving to sharpen the opposite side, using the 30 degree inclusive slots. The spey gets used for deburring conduit, scraping, and rough jobs.

That's always been a strong point for traditionals in my eyes. Multiple blades let you shape them for different tasks. On my stockman from Queen I keep the sheepsfoot extremely thin and hair whittling sharp, while the spey is ground thick at 12 degrees per side and I don't take much time with the edge. If it shaves arm hair I'm content. That's used for things that would dull an edge quickly, like cardboard, with the. The clip I keep sharp and thin as well, keeping it in reserve for food tasks. I strongly prefer a Spyderco hole to nail nicks though so I don't carry my Queen often these days. Very good knives though.

Durability in cutting is not the only consideration. Take a RADA cutlery santoku down to 24 degrees inclusive and cut with it and you'll be pleasantly surprised. Run it through the dishwasher and you'll be jumping up and down from the nicks that have to be repaired.

What would I put a knife in the dishwasher for? And 24 degrees is on the thick side to me for a food knife. Most kitchen knives have much better geometry than tactical folders though so cutting ability would still be good with the 24 degree edge.

 

[me2]

Alvin, is that you?

Check out Cliff's reviews of some of Alvin Johnsons knives. I think Dexter Ewing or Joe Talmadge did some too. They are well above acceptable norms for hardness (HRc 63.5 is the lowest I've seen) and typically have included edge angles of 8-10 degrees, 4-5 degrees per side. Alvin has cut metal flashing with them from abrasive wheel cuts without chipping or cracking. Spine thicknesses are typically 1/16" or less, with edge geometries of 0.02" 1/4" back from the cutting edge, typically a few thousands at the edge itself. And yes, if you push them too hard, they loose a large half moon from the edge.

The RADA knives have a relatively low hardness, so very thing edges fold quickly. I didnt say you'd put a knife in the dishwasher specifically, I was using you in the general sense. I generally dont put them in there either, but when I'm not around, knives end up in the dishwasher, and it takes several sharpenings to get the dings out. I dont cut on ceramic plates either, but I leave the edges at higher angles because I'm not the only one that uses a knife in the house. Also, for kitchen knives in general, I think impact with the cutting board dulls them more than the food itself.

The metal cutting I do ranges from cutting copper wire to cutting tie wire to deburring metal conduit. I once batoned a knife into 22 gage sheet metal. The knife would have been fine if I'd used perfect technique, but it twisted and took a chip out not quite as deep as the edge bevel. It was 154CM at 17/20 degrees (beveled at 17 and microbeveled at 20). Cutting metal is very technique dependent. Had I not twisted in the cuts, my Sharpmaker would have fixed it pretty quickly.

I've said before, somewhere, my ideal balisong (which is my favorite EDC) is an M2 blade, 0.05" thick, with a full flat or convex edge, hardened to about HRc 65. This would handle all but the sheet metal batoning and the deburring I think. Cutting tie wire and copper wouldnt be much of a problem I dont think.

 

[Vivi]

Alvin, is that you?

Check out Cliff's reviews of some of Alvin Johnsons knives. I think Dexter Ewing or Joe Talmadge did some too. They are well above acceptable norms for hardness (HRc 63.5 is the lowest I've seen) and typically have included edge angles of 8-10 degrees, 4-5 degrees per side. Alvin has cut metal flashing with them from abrasive wheel cuts without chipping or cracking. Spine thicknesses are typically 1/16" or less, with edge geometries of 0.02" 1/4" back from the cutting edge, typically a few thousands at the edge itself. And yes, if you push them too hard, they loose a large half moon from the edge.

The RADA knives have a relatively low hardness, so very thing edges fold quickly. I didnt say you'd put a knife in the dishwasher specifically, I was using you in the general sense. I generally dont put them in there either, but when I'm not around, knives end up in the dishwasher, and it takes several sharpenings to get the dings out. I dont cut on ceramic plates either, but I leave the edges at higher angles because I'm not the only one that uses a knife in the house.

The metal cutting I do ranges from cutting copper wire to cutting tie wire to deburring metal conduit. I once batoned a knife into 22 gage sheet metal. The knife would have been fine if I'd used perfect technique, but it twisted and took a chip out not quite as deep as the edge bevel. It was 154CM at 17/20 degrees (beveled at 17 and microbeveled at 20).

I've said before, somewhere, my ideal balisong (which is my favorite EDC) is an M2 blade, 0.05" thick, with a full flat or convex edge, hardened to about HRc 65. This would handle all but the sheet metal batoning and the deburring I think. Cutting tie wire and copper wouldnt be much of a problem I dont think.

I've seen some of Alvin's work. I'm impressed with it, but not surprised. Maybe once my income increases I'll be able to venture more into custom knifemaking and get specific steels at RC's with very acute edges that I can play around with. I've already asked Koster about a 64RC 13C26 knife. I'll get that sometime down the road.

I'm surprised the 154CM blade chipped at that thickness. I'll have to start picking up scrap metal to cut so I can get an idea of what it takes from a knife to be able to handle it.

Have you tried going to a custom maker for an M2 blade like you describe? If you ever get a hold of one I'd love to see some results for edge retention, durability etc.

 

[sodak]

I have a couple of M2 blades that were a gift from a fellow experimenter on rec.knives. I found a source for HSS M2 power hacksaw blades at 65 - 66 HRC, and snagged a bunch of them. I sent a couple off to this guy, and in appreciation he sent me a couple knives. These power hacksaw blades are huge.

Anyway, these knives will cut like there's no tomorrow. The only knife that I have that will stay with them is a Phil Wilson custom in CPM 10V at 64.5 HRC. It will outlast their edges in slicing abrasive media, but they will hold an edge 3 - 5 times longer than ANY of my other knives. This includes D2, S30V, anything. That high hardness and thin edge does the trick.

 

[me2]

Hey Sodak, any info on getting a hole in these things? I'm about 1/3 the way through the M2 blade you sent me that was .055" thick. Thats for the first hole. Looks like cord wrap and stick tangs for now. That .1" blade is a beast. I havent even tried it yet. Did you get the nessmuk made you were planning on? Any chipping or toughness issues so far?

Vivi, like I said on the 154CM, I twisted in the cut. The axe head came down and hit a little off center, and the blade twisted while the edge was about 1/4" into the sheet steel. Sheet steel is probably about as bad as it can get, with the small contact area and high force needed to cut. OTOH, I've cut aluminum cans over 100 times with a Schrade peanut and it would still shave, though not as smoothly. That blade tested at HRc 58. The edge angle was about 18 degrees, there was no twisting, and the metal was too thin and weak to cause a chip anyway.

 

[sodak]

Me2, I've given up on the holes, going to be using epoxy. Carbide tips just aren't cutting it, nyuk, nyuk, nyuk... I haven't made much progress on the nessmuk, trying to rest the elbow for a while first.

I've had no problem with the other knives chipping at all. I haven't done any prying (and don't plan to), but with the 0.1 stock, I don't think a small amount would be bad. Those hacksaw blades are beasts, can't imagine that the knives made from them will be too delicate!

 

[me2]

There was a fellow on rec.knives that bit the bullet and made a machete out of his large 0.1" blade. He reported minor chipping, but I dont remember his geometry, or what he was cutting. I'll be tarred and feathered if I didnt just run out of handle wrapping leather, so it looks like stick tangs now. Imagine a puukko out of this stuff, at 0.1" thick. Edge holding = , sharpening = (where's the crying in the fetal position smiley?)