Japanese garden machete (nata) : an example of the benefits of the chisel grind

This is a very simple example of the ability of a chisel grind to cut at very low angles and how it allows cuts which can not be performed by a traditional blade with a heavy secondary bevel.

Category:

Education

Tags:

• japan
• woodworker
• nata
• garden
• machete
• chisel
• grind
• stake

[CliffStamp]

@docnightfall But, I use WAY too much force. There is no need to use half the effort I am doing if your intention is just to cut the wood in two pieces. But again I enjoy it, I am evaluating the knife for emergency situations, I want to know what will happen if I do chop heavy, etc. (plus it looks way cooler on video).

[CliffStamp]

@docnightfall The goal is to provide just enough counter resistance to keep the blade from doing that (and endangering yourself) and not so much that it can not move at all and thus you would maximize the strain on the edge (but also maximize the chopping power). If you look at my hands during the chopping, I do not have a very tight grip laterally at all for this reason and the blade can rotate significantly.

[CliffStamp]

@docnightfall If you relax during the impact and let the knife move in the cut, the load can only be lateral -if- the medium is strong enough to constrain the knife (really hard woods can still do this) otherwise it will just move instead of being bent by the lateral load. The problem with this is that the knife, in these cases, can come right out of the wood.

[CliffStamp]

@docnightfall Yes, that is it exactly. The edge load is unbalanced even on a straight vertical cut due to the asymmetry in the grind. It will thus tend to rotate. If the wood by its nature produces an asymmetric load (knot, grain, split, etc.) -and- you force the blade to stay true in the cut, the edge will suddenly have a huge lateral strain and all knives are extremely weak laterally compared to compressive resistance - which is basically infinite in comparison (1000:1).

[docnightfall]

@CliffStamp Although, if by saying "relax a little", what you actually mean is "activate gorilla mode", then yes, that would probably induce greater stresses on the edge. :)

[docnightfall]

@CliffStamp I was thinking about it just now and it seems that an asymmetrical edge's tendency to "turn" when it meets heavy resistance is just the edge passively being deflected closer towards the path of least total resistance, which intuitively would be path where the side loads are most evenly distributed. So "relaxing a little"-- using the weight of the knife, letting it impact with a supple wrist-- would probably be good for durability.

[CliffStamp]

@docnightfall I can prevent that from happening by radically changing the bevel and ensure that it will fail first at the edge itself, i.e., in the last 1/16" or so by applying a heavy relief grind there. This will lower the failure point, but cause premature failure to happen in the very edge and not see nothing - nothing - nothing and then the entire convex bevel will deform/dent.

[CliffStamp]

@docnightfall There is that. I do intend to run this again the weekend and relax a little and see what happens, if it is ok I may lay the primary grind back. The problem is though that if this goes it is going to go completely due to the nature of the grind and the way it will be loaded. The entire convex bevel is very likely to deform if over stressed.

[docnightfall]

@CliffStamp I agree, the point of using a tool in the first place is to make life easier, and so in the tool should be made to serve the user and not the other way round.

[CliffStamp]

@docnightfall I could also not act so much like a gorilla when I chop wood and focus more on cut placement than power. The problem is that I don't want to refine the edge to such an extent that if I am using it in the winter, with gloves, in a hurry and do a sloppy and heavy cut that the edge takes a significant turn.

[docnightfall]

@CliffStamp I see. I suppose you could still thin it out behind the edge, raise the bevel line.

[CliffStamp]

@docnightfall As a quick estimate then, the edge would need to be three times as thick (given a specific force/skill) which would mean personally I could not take it much less than 0.075" - which rather ironically is exactly the current thickness of the secondary convex bevel.

[CliffStamp]

@docnightfall The problem is that the asymmetry of the chisel grind means that side loading is very significant and thus it is much weaker than a v-grind of the same cross section. Normally the side loading is just the unbalanced forces, on a chisel grind the side loading is essentially proportional to the force used in the cutting. This means chisel grinds are loaded laterally an order of magnitude greater.

[docnightfall]

@CliffStamp I'd love to see how it does with a wider bevel and a longer radius on the convexity. The mild steel face grinds so easily, it's just begging to be optimized.

[Warescrackdown]

@CliffStamp  Thanks Cliff.

[SpartanJohns]

Way to go on making a point! Pun intended. :))

But seriously: great demo! It's something really logic, but few people think about it.

Honestly I would have never thought about it!

Great video!

[CliffStamp]

@Warescrackdown It would be difficult to jig shapen due to the multi-faced bevel, in order to keep it as the original profile you have to flat sharpen two bevels and then convex another one. It is not difficult if you are used to hand sharpening, and the steel itself is very simple to sharpen as it grinds easily and has minimal burr formation. But no problem, I will put up a sharpening video later.

[CliffStamp]

@docnightfall Yes, it isn't difficult to fix.I am just letting it stay like it is for now anyway as I am curious to will it wear down in use. Winter is coming now anyway and I have at most a month before I have to wear gloves and at that point all that does is add traction. It does however give snow/ice/water a place to hide.

[knivesfishwild]

nice demo n explanation! :) great point.

[Warescrackdown]

Don't forget to do a video on how you sharpen it. The grind has me and I'm sure others wondering how to approach it.

[docnightfall]

@CliffStamp You could fill the gap with epoxy before sanding it.

[haywoodf]

@knivesandstuff Granted. Unfortunately on some forum posts the disconnect is worse than from poor english skills. Some posters don't even spend the effort to read enough or any context and then parrot hearsay barely related. This is a great example of concisely passing information in an interesting way. You both do it well. Any included linguistic challenge is not a problem for me. lol :-)

[CliffStamp]

@knivesandstuff Yeah, it was kind of amusing to see how all the threads, which were at one point a very hot topic suddenly just fall off and everyone sort of hung their head and pretend they were not involved and had not spent post after post trying to explain the tactical nature only to find out it was because some guy behind a camera liked the knife turned the other way.

[CliffStamp]

@knivesandstuff Yeah, there is a reason why chisel, plans, broad axes, etc. all have the grinds that they do. The handle on this though is abrasive to the point it is almost unusable though without rounding out that center cut out, the wood is left raw from the saw cut and as it is oak it is not soft and forms a very hard edge. Again, not a big deal to sand out in any case.

[knivesandstuff]

@CliffStamp everything except the last in fighting is a load of crap.. :) a normal chisel would optimally have you slash across your body left to right for a right handed person. the left side chisel optimally wants you to expose your body and slash right to left.. No matter what.. in a fight you are not going to choose your cut to match the grind. There is not a single remote reason on earth for a chisel grind to be better for fighting otherwise history would be full of them.