Geometry, Toughness and Cutting Ability, info and anecdotes requested

[David Mary]

I have been doing some testing lately, just to try and get a better feel for striking a good balance between toughness and cutting ability. A knife that can chop or baton through a nail is going to be obviously very tough, but how well can it cut? And a kitchen slicer ground full flat to 8 or 12 thou behind a 15° primary edge is going to slice well, but I'm starting to think no matter the steel or heat treat, you're still going to take a half moon chunk out of it if you try and cut a nail.

Spoiler: Some of my observations, nothing scientific.

H1 Aqua Salt plainedge, ground to a thick 15° convex edge and 20° micro, about .030" bte, cut through a nail and showed no damage beyond a little edge roughness that honed out in a couple of passes on ceramic.

H1 Salt 2 Wharncliffe plainedge, reground to near zero, dropped accidentally tip down onto portable carpet square, underneath which was concrete foundation, ~1/8" of tip bent right over.

AEB-L listed at 62.5 RC, ground to .012" behind the edge, spear point tip, 1/16" of tip stabbed into maple, and pried, bent twice, snapped off the third time.

AEB-L listed at 61 RC, .020" behind the edge, batoned a nail, took small half moon chunk out via catastrophic rolling.

8670 ground to .012" bte, catastrophic rolling and chipping when attempting to baton nail.

Reclaimed sawmill blade steel, ground to convex, 15° primary edge, 20° micro, .035" behind the edge, baton nail and showed no damage.

Final note: I made a seax early last year in 1084, tempered to 450°. I ground it to full height flat-vex, with a 15° per side primary edge and 20° micro, and about .020" bte. I tested it outdoors, and it passed through brush like nothing. Then I tested quite hard chopping hard wood. That rolled the edge but only in the spots where I applied the most force. I was able to use a rock and fix the rolling in the field. I suspect if I had batoned a nail, I would have irrevocably rolled a half moon out of the edge and had to regrind.

I tested a second time with more hard wood chopping and this time also batoning it through a very knotty piece of wood. The rolling this time was more severe, and I had to reprofile it slightly on the grinder. After that, I left the edge more obtuse, and though it did not roll any more with hard use, it just didn't pass through brush and small branches like it did before. I never tested it on a nail.

So basically I am looking for opinions and input on just how thin you think a knife should be and still be able to baton a nail, and whether the baton nail test really matters. Should an outdoor chopper be able to baton a nail? If so, won't the geometry sacrifice some bite? And if it will sacrifice bite, then isn't it better to just be careful not to hit rocks, and instead have thin geometry that can bite deep and send chips flying? I know it's all about compromising characteristics, and I am basically just looking to hear others' experiences, anecdotes and opinions on this topic of geometry and the balance between cutting ability and toughness.

Thanks

 

[FredyCro]

I think this sums it up. There are many more destructive test on Nathan's yt channel that show different performances depending on the geometry, thickness and so on..

I think what a lot of makers overlook in the start (including me) is how much more important is the edge geometry rather then choice of steel. I got all involved with steel types and was surprised that even my balcony HT 1075 would cut through a nail and not shatter to pieces.

The nail test is cool, but if you think about it, it's kind of purposeless, if you needed a tool for cutting nails a lot, a knife wouldn't be your first choice, would it?

 

[Stacy E. Apelt - Bladesmith]

I keep a one dollar yard sale hatchet and a couple Bic disposable razors at my table when doing a show.

If someone wants to run the bade up their arm to check for sharpness, I hand them a razor and tell them that is the right tool for arm shaving.

When they want to talk about knifemaker X's you-tube video of cutting nails and chopping on the anvil, I hand them the cheap hatchet, and tell them that is the tool if you want to do such dumb things.

When they ask about FIF, I say, "Yeah, it sure is entertaining, but not very realistic. But, I guess you never know when you will have to chop a buffalo skull in half, then stab a jerry can full of gas repeatedly."

 

[David Mary]

Helpful thank you.

Yes, I think it is a dumb ting to do. Except when trying to discern the limits of your materials, heat treatment and geometry. Granted, I didn't do it methodically enough to submit my observations to a peer reviewed journal, but I felt the need to do these abusive tests (on my own knives, not customer knives!) to further my personal knowledge, even if only anecdotally...

My takeaway so far is that if I want it to cut well, I shouldn't be afraid to keep grinding thin, and if I want it to be indestructible, I should make a hatchet.

 

[David Mary]

my balcony HT 1075 would cut through a nail and not shatter to pieces

I'd be curious to know your temper, geometry and edge profile.

 

[FredyCro]

I'd be curious to know your temper, geometry and edge profile.

I also did it just for the sake of testing, I did a 2x 1h temper at 200 degrees C and tested the blade couple of times between grinding it to the final edge thickness of about 0.1 mm (1" wide blade, 3.5 mm thick, FFG). I would suggest that you do a simple EDC shape, HT and temper it at 0.5-0.8 mm thickness and sharpen after grinding the decarb. Now do some testing, notice the edge damage. Grind down 0.1-0.2 mm edge thickness and repeat the testing. Repeat until final thickness is 0.1 mm BTE. I use this knife in my shop and give it an occasional abuse (prying, scraping and so on). All things being equal as the cutting performance progresses the damage from abusive testing will become bigger. If you want a tough user leave a thicker edge (0.2-0.4mm) or do a saber grind, but consider how it will affect the cutting performance and how this will affect the resharpening down the road.

 

[FredyCro]

But i am also just rambling as it seems that you have more experience then be and already know all this. What i am trying to say is, that I think there is no secret recipe, for example on my recent cleaver project I ground thin, tested and then ground back until the edge could go through a bone without taking damage (short convexed grind).

 

[David Mary]

Thanks Fredy, I appreciate it.

 

[HSC ///]

I work with laminated steel frequently for kitchen knives. After hardening I chop nails or cut steel with the edge to confirm its hardness. I do this with a thick edge.
It’s a simple effective way, So this practice certainly has some use for me.

Harbeer

 

[Horsewright]

I keep a one dollar yard sale hatchet and a couple Bic disposable razors at my table when doing a show.

If someone wants to run the bade up their arm to check for sharpness, I hand them a razor and tell them that is the right tool for arm shaving.

When they want to talk about knifemaker X's you-tube video of cutting nails and chopping on the anvil, I hand them the cheap hatchet, and tell them that is the tool if you want to do such dumb things.

When they ask about FIF, I say, "Yeah, it sure is entertaining, but not very realistic. But, I guess you never know when you will have to chop a buffalo skull in half, then stab a jerry can full of gas repeatedly."

Some of this stuff has always been baffling to me. I remember reading in these pages years ago a guy complaining because push cutting on a 16 penny nail was dulling his edge. I couldn't finish reading the post because I knew the next thing he was gonna do was stick his knife into a tree and use it like a ladder. I have a ladder, I have an axe and a splitting maul, I have a metal cutting band saw and I have a chainsaw. I test my knives by doing with them what they are designed to do. My leather knives are designed to cut leather not nails. They do make their own sheath and if they are slicing through the heavy saddle leather like I like em too I resharpen it.

My small edc ranching knives do edc ranching chores because I wear one every day. I'm using it to open hay bales and feed sacks, castrate calves, cut rope and twine etc. They are not machetes and I don't expect them to push cut nails.