Good article on batoning

[Joe Talmadge]

I've never broken a knife batoning, but don't do it nearly as often as many of you here. Here's a good article from one of the BRKT guys. I usually keep my handle parallel to the ground. The idea of pushing down on the handle causing extra stress seems to make sense, but I haven't tested it at all. What do you all think?

http://www.barkriverknives.com/docs/batoning.pdf

 

[Cliff Stamp]

The angle part is nonsense, the load is actually a maximum if the blade is parallel, that insures maximal force will be directed to induce rotation, thus it is easier on a blade if it is angled not worse - this of course is least effective for batoning because it is the force which acts to rotate the blade which is of course what is also driving it into the wood.

However if you do baton on the tip while resisting the upwards rotation of the handle with your off hand there will be a significant internal strain on the blade as essentially you are loading a beam at both ends. Of course once the blade is fully in the wood you have little choice at that point unless you want to then switch to wedges or attempt to pry the wood apart.

However the internal strain from batoning is fairly low, note what you are arguing is that it is easier for the steel to bend rather than be driven through the wood which indicates a rather large problem. Of course the knife in question has to be considered, I could easily break any number of small knives with significant batoning, but they would all go through the blades not the tang.

This however doesn't get extended to all knives, that is just silly, it would be like saying chopping is abusive because if you chopped hardwoods with a hollow ground hunter it would break. This is a case of weakness of design being used to advocate abuse, it is the same thing that happens when Mike, you and Steve started noting problems with liner locks, there was a huge outcry that white knuckling, spine whacks and torques were all abusive.

It is trivial to find makers and manufacturers who will not call this abusive, because it doesn't take much in the tang to prevent it from failing. I have noted this publically in the past. Note as well that lots of other types of knife abuse will generate very large internal stress of the same type, use a very knife for very powerful stiff wrist chopping or any large blade that sees an impact that you resist, consider martial purposes.

Note in particular blades with pommels take huge internal forces on the tang when the pommel are massively accelerated during a sword impact (essentially the pommel is rotating during the swing and it has to stop just as violently as the blade which means the tang and it undergo a large action/reaction force). Would you call it improper technique and blame the user if this constantly caused the tangs to crack off.

Yes some knives have to be limited with batoning to no off hand pressure because the tangs are too weak by design, it is therefore abusive to them just like it would be abusive to use a 1/16" martindale machete on hardwoods as the edge would be mangled, but perfectly acceptable for the 3/16" martindale bolo which is designed to take said loads.

Note some woods require off hand pressure and really heavy baton weighs in order to split. I have seen even 4-6" wood which was twisted and knotted take dozens of impacts from a heavy baton (as in several pounds) with each impact only making a 1/4" of travel, and if the off hand was not used on the handle, the blade would just rotate and not move down into the log at all.

-Cliff

 

[Joe Talmadge]

Thanks Cliff, I vaguely remember seeing you argue this before, that holding the handle this way is not abuse.

 

[Jeff Clark]

The issue is not the angle of the knife per se, it is the location of the fulcrum that is increasing the stress. If you hold the blade parallel to the work surface and hammer in the middle of the blade the blade will be supported over a wide area with minimal torque on the tang. If you hammer an overhanging point the fulcrum will effectively be close to your impact point (on the point side of the blade). With a short lever arm between the hammer and the pivot the torque on the blade will be low. If the wood was narrow and you positioned it adjacent to the guard and hammered near the tip the fulcrum would be far from the hammer and the torgue would be high. You get the same effect if you tilt the handle down on a thick piece of wood and hammer near the tip.

I think one issue we see in these knives that have broken is that the tang is hard rather than soft. I don't think you'd see a scandi knife break in the way seen in the more expensive knives since the tangs as soft. They will simply bend rather than break. If you have a narrow tang is subject to higher stresses since it has a smaller cross section. In addition the transition zone between the full width blade and the narrow tang is a site for stress concentration. If you are going to use a narrow tang you need to reduce its hardness all the way up beyond where the blade necks down to the tang.

On the old Kabars and bayonets I learned long ago that the handles would bend when I threw them. Then handles would bend, but never break. When I was young I saw this as a design flaw. Now I see it as an essential part of a stick tang design used for heavy work.

 

[Cliff Stamp]

... that holding the handle this way is not abuse.

The arguement is essentially that an inability in some knives should be extended to every knife. I could easily break the Mora 2000 by heavy batoning, the plastic handle would shatter and the blade would twist/warp, so I can't use off hand loads, which means it is for light batoning only, of course this doesn't mean I place the same limits on a Ratweiler. The ability of the Ratweiler to take large off hand loads makes it much more productive on harder to split wood.

The issue is not the angle of the knife per se, it is the location of the fulcrum that is increasing the stress.

The angle of the blade is argued specifically, this came about when failures occured when the blade was off parallel (because it naturally goes off parallel during heavy batoning) and a number of people advanced the idea that this itself was causing the problem, it is completely false and in fact the opposite is true.

If you hammer an overhanging point the fulcrum will effectively be close to your impact point (on the point side of the blade).

If the wood is perfectly even, the internal bending moment will be maximum in the middle of the two loads (your hand and the baton being the loads). There is no central fulcrum, the force isn't focused on the tang, the entire blade is under a internal torque which is minimal near the points where the force is applied and very high in the middle, it is basically an upside down v. The tang will often break first simply because it is the weak point in the design.

However the internal bending moment is rarely that uniform as the mechanics are complicated by the fact that the wood isn't even, if there is a knot for example this will act to focus the load and the bending moment maximum will shift to that point strongly. Thus if you want to put maximum strain on the tang, position the blade so that the choil is right next to a knot, this is likely what tends to cause most problems as it will make the internal strain very high near the blade / handle juncture. To minimize strain on the tang you would position the tip so it cuts through any necessary knots.

Mechanics by Benedek introduces this subject, internal stresses, it is usually left out of introductory university physics which assume all support objects are perfectly rigid and usually weightless (ropes, beams, levers, etc.), but Benedek treats them as real objects in some detail and then examines their breaking points. It also does a lot of biological examples, how much of a fall can you absorb still legged before the internal forces will cause the bones to break, etc. . Nice introductory book to the physics of fracture and breakage using real objects in dynamical situations, makes the mechanics a little more real.

I think one issue we see in these knives that have broken is that the tang is hard rather than soft.

Little attention is put to these in general, note the difference in the tang construction of Busse vs Cold Steel which Turber revealed when he cut the handles off a Basic and Trailmaster. It just goes back to R&D, how many knives are actually destroyed to examine the steel and geometry.

-Cliff