Breaking two blades

C

Corduroy

Joined
Apr 15, 1999
Messages
1,442
I apologize for not posting this sooner. Last Monday, a friend and I deliberately broke two of my knives. It wasn't a "test" per se,I just wanted to see what would happen. I've seen broken knives (not mine) but never seen it happen before.

The first knife was a drop-point hunter in the same pattern as the one reviewed here: http://www.bladeforums.com/ubb/Forum3/HTML/000624.html
The knife has a 4.5" blade fully flat-ground from 3/16" ATS-34 and treated by Texas Knifemaker's Supply. The handle scales are beautiful water buffalo horn. I ignored the common warning to dry natural materials myself and trusted the distributor to have these properly stabilized; after a year they shrunk and pulled away from the handles in some places, ruining the knife. Thank goodness I hadn't sold it!

The knife was clamped securely in a vice 3/5" from the handle. I donned protective wear while my "observer" stayed about 20' back. I put a 2.5 foot "cheater" PVC pipe over the handle and began to bend. At 10-15 degrees the pipe split and the blade returned to true. I then locate a 2.5 foot metal pipe and began again. I could see in the mirrored blade that it was curving evenly, a neat sight. At 25 degrees it snapped off where it was clamped, 2.5" from the handle.

The break was clean, straight vertical and with a rough but almost flat breaking face. It didn't appear to correspond to the filework in any way.

The next knife was a 4" hideout tanto flat saber-ground from 3/16" ATS-34, again treated by TKS. It had served as an experiment for point geometry and a rubber handle material I was trying out, and was unsuitable for sale.

It was clamped 2" from the handle and pressure applied again with a 2.5 foot metal pipe. It appeared to bend fairly uniformly but at 30 degrees it snapped just under 1" from the handle.

The break was again cleanly vertical, but showed some uneven-ness on the face. it also corresponded pecisely to a file-nick on the spine for thumb purchase.

What to make of this? I dunno, and that's why I'm posting for those with more experience to comment. I didn't expect much from uniformly treated ATS-34, but I can't imagine these forces occurring in even the dumbest or most desperate using conditions. The drop-point acted pretty-much as I expected it to, though I'd like to compare degrees of flex to others who have broken such short, stainless blades. I am a bit concerned by the tanto's odd breaking point. I don't think the file nicks caused the break so much as decided where it would happen, but the rough breaking face leads me to wonder if their may have been an impure pocket in the steel.

Well, those are just results, not so much conclusions. I look forward to your comments.

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-Drew Gleason
Little Bear Knives
 
Drew, how much force were you exerting? Could you have done it without the pipe? Was it harder or easier than what is necessary to break a 3/16" file for example?

It would be interesting to see if the breaking point could be varied by use. For example take a couple of knives and beat the crap out of one. Numerous hard impacts on the edge and spine for example. And then repeat the above on both and see how much gross strength was lost.

In terms of surface formation. Every blade that I have seen break before it should have has always had a very rough or jagged face. In contrast blades snapping under extreme stresses tend to have very smooth surfaces.

On a positive note, both blades took a decent flex before breaking. At 30 degrees you would know its probably time to slack off.

-Cliff
 
Geez, so many knives are tougher than we think they are. I'm impressed that it took a 2.5 foot pipe and over 25 or 30 degrees of flex before they let go. I would think this is harder than many of us use our knives. I know it is in my case. If I managed to put enough pressure on a blade, by hand, that it starts to flex a significant amount, I'm the type of person who might start looking for a different tool, but that's just me. In an outdoor or survival situation, however, we know that all bets are off. Thanks, Drew, some very interesting information you brought to us.

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Don LeHue

The pen is mightier than the sword...outside of arm's reach. Modify radius accordingly for rifle.


 
Wow, interesting details Drew.

I know you're looking for technical feedback, but you won't find them here...but there's something oddly profound about the deliberate breaking of a blade, even for testing.

Must've watched too many movies this weekend.. one movie (Hunted) had a samurai breaking his katana by slamming the point into the floor and then snapping the blade with a pull on the handle (rather than handing it over to the police). The other movie (By the Sword) had a fencing instructor breaking a rapier (across his knee, I think).

I'm surprised that there hasn't been a lot of studies already done by others, and maybe by manufacturers... although the latter may consider their results to be a proprietary competitive secret. This would seem to be a test that's difficult for any single custom maker to do on a significant scale in order to factor in different material sources and other things.

From the peanut gallery: Possibly the uneveness of the break in the saber ground tanto resulted from a different distribution of stress forces (than the flat ground), since the cross section of the drop point is more uniform?
 
Coruroy,how long should it take for water buff horn to stabilize?I have some that is oversized and will sand it down flush with pommel and bolster.

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Mr. Stamp,

I certainly couldn't have snapped these knives off with my bare hands. I wasn't straining on the end of that 2.5 foot pipe, but on the 4-inch handle I wouldn't have had a prayer. Maybe some big beefcake fella could, but I doubt it. You definitely would know you were doing something very bad well before stressing the knives this much... but I feel that's true of any decent fixed-blade with an intelligent user (unless the knife genuinely has flaws in it, like the first MadDog you tested, for example). I was testing how it broke, not if I could break it. If a user did this to one of my knives in use, I'd be very critical of the way they were using it. I'd still replace or refund it, but I'd definitely want "the story." I (unlike some) wouldn't tell a user that my knife could stand up to this kind of abuse.

Mr. LeHue,

I do feel that 25-30 degrees of flex over 2-3" of blade is pretty darn good, but I'd like to hear from others for comparison. Certainly outside the bounds of "acceptable use."

Ghostsix,

I don't know how long to dry buffalo horn for. I'd say either leave it out in a dry place at least a year, or put it in a drying cabinet for a few weeks. Just guessing though. Heed my mistake and don't ever trust it to be stabilized already, no matter where it comes from.

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-Drew Gleason
Little Bear Knives
 
Drew :

If a user did this to one of my knives in use, I'd be very critical of the way they were using it.
Click to expand...

As you should be since you have well defined the bounds. You seem to be a straight forward fellow and I have no doubt that you would be on the level as to your knives performance in any areas - durability or other wise. It someone deliberately exceeds the discussed expectations then obviously the problem is not yours.

As an aside to this, related to durability in a way. As you have been asking questions concerning geometry lately. How do you (and anyone else of course) feel about full grinds (no edge bevels)?

I really like the performance they give and how easy they are to maintain. My only problem is that they are fairly fragile even when compared to a 15 degree bevel. Have you ground and blades like this and would you considerable them suitable for normal use?

I have been leaning towards this as of late as with the new standards being set by some of the high performance alloys like the CPM steels and Talonite it only makes sense to go with optimal cutting grinds that take advantage of their over average durability.

-Cliff
 
Mr. Stamp,

Just in case we're unclear, when I refer to a knife as "fully ground" it may still have an edge bevel; I mean only that it does not have any portion of the blade width left at full stock thickness (saber-ground).

As for your question, I feel that fully grinding blade with no edge bevel is an excellent way to go on a convex-grind but is unsuitable for flat- and hollow-grinds. The reason for this is that sharpening is in effect re-grinding the bevel that leads to the cutiing edge. If that bevel is the entire width of the knife, you must effectively regrind the knife every time you need to sharpen it. Too much work! Also, most bevels are in the 17-24 degree range for strength, while I consider this much too steep an angle for an entire blade grind because the knife would be too thick and have lousy cutting performance. I favor primary grinds in the range of 5-12 degrees. None of this quite applies to convex grinds because it is possible to slack-belt or strop just the edge of those without refinishing the whole blade. This slowly makes the angle at the edge more blunt, so occaisionally the knife should be completely reground, but at least it's better than regrinding it every time it gets dull.

I have heard much good reasoning behind hollow-, flat-, and convex-grinding. The first gives the thinnest edge while the last leaves the most weight behind the blade. I choose the middle road because I don't have equipment to hollow grind, I find most folks dislike convex grinds and think they're hard to sharpen (they aren't, IMO), and because the flat-grind seems like a fine, simple compromise between the two. I usually think that since a knife is just a big wedge, it should have the steepest possible angle. For this reason I'd rather make the stock slightly thicker or make the blade broader if more strength is required, rather than saber-grinding. I may re-evaluate this in light of the discussion on full-grinds sinking too deep in chopping. Gotta try some things out and see.

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-Drew Gleason
Little Bear Knives
 
Drew, I can't readily see why you differentiate between convex and hollow/flat in terms of being suitable for flat grinding because of sharpening ease. If you could do touchups on the convex grind focusing on the edge could you not just do the same with the flat or hollow grind? You would follow the same logic, eventually as this thickens you would want to recut the primary bevel.

The weakness you mention is a problem though. I will admit that one of the reasons I will probably go with no bevels from now on on custom jobs is that I don't have to do any edge thinning as its already at the weakest stage. If I find the edge too weak with no bevel I can just add a slight one and work up until I get the minimum profile with the necessary toughness.

I am very interested in this grind though as if left as it is (maintaining the whole grind and not putting a bevel on) gives optimal cutting performance. I would be very interested in any experience you have in that area so if you do test pieces or whatever I would appreciate hearing about the results.

Ed Schott does flat grinds with no bevels in 3V. I have one of his blades now. It has held up so far on ropes / webbing and such and as well chopping on soft woods. I will be very impressed if it suffers no indendation on hardwoods.

-Cliff
 
Mr. Stamp,

It's a geometry issue. Draw a couple of cross sections really quickly. On a convex grind, you can continue to "roll" the grind into the final edge so as to just work on this area. On a hollow or flat grind, there is no way to focus on just the edge without putting on a secondary bevel with your work. To keep the constant grind right to the edge, the hole blade must be reground. Convex grinds let you "cheat" by steepening the curve as you work on just the edge. I'm not saying that you can't work on just the edge in a hollow or flat grind, but the moment you do, you have created a secondary bevel.

-Drew
 
Drew, I think we are just looking at it slightly different. Are you are just saying that on a convex grind you can flow the bevel into the primary grind so the distinction between the two is fuzzed out somewhat and the shape of the grind can be retained closer to its natural state?

Yeah, I can see that. My point is just that unless you work along the full grind shape you are creating a bevel. Of course if the bevel starts back 1" on the blade then its not really a bevel but you have a sort of double ground blade. Semantics.

-Cliff
 
I don't think horn can ever be "stabilized" to the point where it will never move again. Differences in temp and humidity will cause horn - and some other natural materials - to change shape.

Stag can also change shape, but isn't as temp sensitive as horn.

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www.wilkins-knives.com


 
Mr. Stamp, I do think it's mainly a semantics issue. With the convex grind you can just flow the primary bevel (grind) into the secondary bevel (edge bevel) so there really is no distinction between the two. It amounts to sharpening the bottom 1/2" or so of the blade width to an increasingly blunt convex edge, and every now and then taking off some of the blade higher up to thin this out. Convex edges are pretty odd things, but I have no doubt of their great performance. I don't think most buyers care for them, but I've put them on some things I've made for myself.

-Drew
 
Drew, I think a lot of the dissatisfication comes from the fact that they (of course) respond very poorly to normal sharpening techniques. You take your lansky and grind away on the Moran and all it does it lower the shoulders without doing anything to the edge.

As you noted the technique is not extreemly hard, but it does require freehand work. However with regular steeling, stropping and some light work on a ceramic rod you could extend the life of a good edge for a long time. Doing this you could probably get away with just sending the blade back to be resharpened if you didn't want to learn how to regrind the bevel.

One of the things I like in a maker is the willingness to discuss his work and choices. For example when I had Mel Sorg make me a small utility knife awhile back we went over v or convex grinds for the bevel and discussed performance and maintance issues. You have shown the same tendancy in your posts and I would bet this is a large part of why people are so satisfied with your work as they know exactly what they are getting - no hype, just performance.


-Cliff

 
Mr. Stamp,

I appreciate your kind words. I am really quite new to this and haven't the experience of many on these forums, so my unwillingness to make performance claims often comes from simple lack of data. I try to tell what I see and what I think because I simply lack the raw making and testing hours that let others state facts rather than opinions. It's feedback from folks like yourself that will let me gather info and test my opinions, so I try to keep an ear open. I do have a stubborn side, though, as I'm sure some posts have shown.

Customer input into the knife design and construction process is critical to my definition of the "custom" knife. I don't consider every handmade knife "custom" - it is custom when the buyer has input into what is made before hand, whether it's an entire design or simply "just like that one, but with brass pins." It's a knife made for a certain person, the way they want it. I enjoy it when someone has an idea, a drawing, or a concept that they want put into steel. I have plenty of my own ideas to keep me busy, but in many ways acting as the bridge between a knife lover and the knife they have in their mind is more enjoyable than making my own designs.

I want to thank everyone on Bladeforums for giving me the impetus I needed to get back to my knife work. For two years my shop has languished while I finished school, but this past weekend I ground three blades, profiled and laid out a folder design for a friend, and did some Benchmade work as well. I was very tired for class on Monday, but very happy as well. Many thanks to this community for letting me rediscover this love that I had set aside for a while.

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-Drew Gleason
Little Bear Knives
 
i have an old copy of a california knifemakers association letter with an article about the above.....took two heavy weights to break a 1/4" 154cm big bear... and the conclusion....you would have to try really hard to do anything to a properly heat treated blade out of modern exotic chrome moly (actually it said you would be a simmering hunk of flesh laying next to your broken knife)....one comment on the above test... you should have tried some knives from different heat treaters.....especially if youre using the same steel...same thickness....same knifemaker.....

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http://www.mayoknives.com


 
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