Recommendations for Machete

[P.Brewster]

Can anyone recomend a steel, where to buy it, final desired hardness, and edge geometry for a medium-sized kukri/machete field knife? Method will be stock removal.

 

[flatgrinder]

If you can heat treat it yourself:
I would recommend some 1/8" thick x 2" wide 1095 from Admiral Steel. Flat grind it to .020", heat treat, after heat treat, give it a full convex edge. You can get creative with clay quenching in Parks and temper at 385-400.

If you can't, use some A2 in the same size (from flatground.com) and have Paul Bos heat treat it for you to HRC 60.

 

[P.Brewster]

I'm totally new to knife making, and at the moment I think of myself as a knife designer.

that being said, I plan to have the heat treating done by Boss or someone else.

I also plan on using 3/16" thick stock for weight.

You said "Flat grind it to .020", heat treat, after heat treat, give it a full convex edge." Do you mean grind it until I'm left with a 0.02" stripe of edge? What is a "full" convex edge? Is it one that starts all the way back on the spine of the knife?

What angle should I grind to? I plan on doing this on a surface grinder.

For purposes of my enlightenment, why do you recomend the 1095 and the A2?

Why a RC of 60? (I'm not questioning your judgement, I just want to learn the concepts).

Thank you.

 

[mete]

I would choose 5160 or L6 and harden to 55-57 HRc for toughness. Other details depend somewhat on the design.

 

[the possum]

I agree with mete on 5160 or L6- according to the books at least, both of these steels have more impact resistance than either A2 or 1095. Meaning at reasonably high hardness, they will still be tougher and more resistant to damage from whacking an occasional rock or nail in the wood, etc.

I like your idea of starting with 3/16" thick stock, but I would definitely design it with some "distal taper", meaning the blade gets progressively thinner towards the tip. Anywhere from 15-30% reduction in thickness, depending on your goals. Taper the tang as well. This will enable you to accelerate the blade much faster for light brush, be less fatiguing to use over extended periods, transmit less shock to your hand on hard impacts, and still give you the versatility to hit with good power on thicker/heavier wood.

 

[Keith_H]

Remember that you cant always make your dream knife from the start, especially if you are heat treating your self (I am not attempting a A2 heat treat at home yet) keep it tough as well as nice and simple. a full convex edge is where the edge curves to a point for extra toughness.

 

[Nathan the Machinist]

snip
A2 in the same size (from flatground.com) and have Paul Bos heat treat it for you to HRC 60.

I recently made a machete from A2, with a target hardness of RHC 60. Took a great edge.

After it broke I found that the part that used to be the tip makes a handy little hand tool with good edge retention for doing dry wall work. Feh.:grumpy:

 

[mete]

Chris Reeve uses A2 for his one piece knife but I do't think it's 60 HRc.

 

[P.Brewster]

Thanks for all the info... I appreciate the conversation of toughness vs hardness; that is what I was wondering about.

I am planning on tapering the tang but I actually want as much weight as possible at the tip for chopping.

Who sells L6 and 5160? What type of steels are they? Spring steel, tool steel?

Thanks for the grind diagram. I knew what a convex grind is, I was just thrown off by the "full convex grind."

This is the insiration for my design for those looking for a mental image:
http://www.gsakai.co.jp/jp/english/shop/natack.html

thanks

 

[the possum]

You can get 5160 all over the place; possibly even locally. Check the yellow pages for leaf spring manufacturers or steel suppliers & you can save shipping cost (which will likely be more than the steel itself.) L6 is sold made by Carpenter Steel and Crucible, but they are just different enough in their chemistry that you have to treat them differently when working it. Recently someone here said Carpenter had some L6 in 1/4" thick stock, but I haven't called them to confirm myself. Their number is 866-790-9092. If not, the thinnest stock made is 3/8" thick, which may be a problem if you don't forge.

Now, as to this part-

I am planning on tapering the tang but I actually want as much weight as possible at the tip for chopping.

I feel obligated to point out the relationship between mass and dynamic properties (such as handling characteristics & chopping power) is not so simple. If you want an axe, you need an axe. Trying to leave extra mass in the tip of a big chopping blade will likely result in a knife that is neither fish nor fowl, and will not work as well as either. You may not want to get this technical with this piece, but I'd suggest checking out this thread to see what I'm talking about. It's possible to gain chopping power at the tip by reducing mass there.

 

[P.Brewster]

Thanks for your thoughts. I know this is a subject of much debate, and I certainly plan to explore this relationship firsthand through my design.

I swing a hammer all day for a living, so this is the source of my ideas about mass location. I'm not a big guy, and I've found I can drive a nail faster/stronger and with less fatigue with a 20oz hammer that with a 22 or 24 oz hammer.

I've also noticed that a hammer with a heavy, big handle is less powerful/fast than the same hammer with a light, thinner handle. To logically extend this observation, a hammer with a solid lead handle has almost no mechanical advantage; you might as well pound on that nail with a big rock.

In general, I agree, reducing mass at the tip can be the key to power/speed; this is supported by my experience with the 20oz hammer. It is also supported by this formula:

F (force) = m (mass) x v (velocity) ^2 (squared)

Which means: if we double the mass, we double the force. But if we double the speed, we quadruple the force. The assumption is that if a blade/hammer is lighter, we can swing it faster.

Then there is the subject of fatigue, which (for me) mostly comes from either stopping a swing (oops thats my thumb) or raising the tool up from a swing. In my opinion, this is (for the most part) a matter of overall mass (rather than mass distribution... obviously, if I hold the hammer backwards, by the head, its going to be easier to raise than if I hold it by the handle, so this statement is not technically true...).

So the concept I'm working with is this:
Chopping speed, power, and lack-of-fatigue are best maximized in a tool with a low OVERALL mass, but with the mass distributed towards the tip. Think of a 12 oz hammer: it's light, but can still drive a nail.

You said "Trying to leave extra mass in the tip of a big chopping blade...," which I agree with. But I'm not making a "big" chopping blade, I'm making a "small" chopping blade, and I think thats the key. A big chopping blade is akin to the theororetical hammer with the lead handle - the mechanical advantage is nearly lost, so any removal of weight can only increase speed and therefore force.

To sum up what I am trying to say:
I am looking at the hammer for inpiration. In the hammer, no attempt is made to balance out the mass, or locate the mass anywhere but the tip. With hammers, if you are having a problem with fatigue, speed, or power, you just use a lighter hammer. (To keep things simple, I didn't bring up handle length, which is a whole other issue... for my machete, I'm assuming an overall length that I want to be carrying (also just like a hammer!)).

Time will certainly tell if I'm on the right track with this.

 

[Stacy E. Apelt - Bladesmith]

I would NOT use 1095 for a machette. I suggest 5160, or L-6 ,or 15N20, or 1070 would all be good choices. Temper high to get extra toughness.
Stacy

 

[the possum]

Since this is not gonna be a really huge knife, you're probably in an overlap area where either method could work with some success.

Like I said, if you're going for something with the mass distribution of a hammer, use a hatchet or tomahawk. Or maybe if you want the longer edge, you could go with a cleaver-

Just keep in mind whether you actually see any of that chopping power will depend on your target(s). A hatchet absolutely sucks at clearing small brush, because you can't get enough accelleration. You don't see the benefits of having that mass forward until you start chopping pretty solid/thick wood. (which is not what I'd design a smallish machete for in the first place)
As as general rule, I'll always prefer to increase chopping power through blade length (and therefore speed) rather than adding mass to a shorter knife. Just seems to suit my purposes much better, and gives much more versatility.

 

[the possum]

There are folks far more qualified than me to talk about the physics involved with chopping, but I'm interested in the subject all the same. Some thoughts-

I'm not a big guy, and I've found I can drive a nail faster/stronger and with less fatigue with a 20oz hammer that with a 22 or 24 oz hammer.

Assuming all three are of the same basic design, then you've simply found the one that best suits your personal strength/physique. Someone who's very strong and slow may prefer the heavier one; someone wiry with cat-like speed may prefer an even lighter one.

I've also noticed that a hammer with a heavy, big handle is less powerful/fast than the same hammer with a light, thinner handle. To logically extend this observation, a hammer with a solid lead handle has almost no mechanical advantage; you might as well pound on that nail with a big rock.

Very astute; thanks for bringing that up. It further confirms my thoughts here...

In general, I agree, reducing mass at the tip can be the key to power/speed; this is supported by my experience with the 20oz hammer.

Either one could be taken to the extreme and be less effective. There is a limit to how fast you can swing your arm regardless of the blade weight, or how heavy a blade you can still swing at reasonable speed.

It is also supported by this formula:

F (force) = m (mass) x v (velocity) ^2 (squared)

Which means: if we double the mass, we double the force. But if we double the speed, we quadruple the force. The assumption is that if a blade/hammer is lighter, we can swing it faster.

This is a little too simplistic a formula, as you noted above yourself. If your hammer had a lead handle, it still wouldn't slow down your swing very much since the weight is close to your hand. Yet power goes way down, because of the way mass distribution affects the impact mechanics.

Then there is the subject of fatigue, which (for me) mostly comes from either stopping a swing (oops thats my thumb) or raising the tool up from a swing. In my opinion, this is (for the most part) a matter of overall mass (rather than mass distribution... obviously, if I hold the hammer backwards, by the head, its going to be easier to raise than if I hold it by the handle, so this statement is not technically true...).

Yeah, I think you just disproved your own theory. Linear and rotational dynamics are controlled by slightly different properties, yet the two affect each other during swings. On second thought, this part could take a while to get into, so I'll wait & see if you're even interested first.
Actually there have been some good threads on it in the testing forum: Chopping Physics, andChopping Physics II. I tried starting a third thread on the subject but didn't get much interest, so feel free to bring that one back if you'd like to discuss it.

I am looking at the hammer for inpiration. In the hammer, no attempt is made to balance out the mass, or locate the mass anywhere but the tip.

And my point is I don't think there's any practical way to make a "machete" with the same mass distribution as a hammer. It sure wouldn't be a knife or machete any more. The hammer (and axe) works because it has a lot of mass clustered at the end of a light shaft. How are you gonna get over 3/4 of a pound of steel in the last few inches of your blade? How will you do so while keeping the rest of the blade and handle light? Because if you can't do this, it will not work like a hammer, and if you try, it will probably not work like a machete anymore, either.

 

[P.Brewster]

There are folks far more qualified than me to talk about the physics involved with chopping, but I'm interested in the subject all the same. Some thoughts-


Assuming all three are of the same basic design, then you've simply found the one that best suits your personal strength/physique.

Exactly, I agree.

Either one could be taken to the extreme and be less effective. There is a limit to how fast you can swing your arm regardless of the blade weight, or how heavy a blade you can still swing at reasonable speed.

This is a little too simplistic a formula, as you noted above yourself. If your hammer had a lead handle, it still wouldn't slow down your swing very much since the weight is close to your hand. Yet power goes way down, because of the way mass distribution affects the impact mechanics.

You're right; I believe there is a formula for momentum that contributes to the force of the blow.

Yeah, I think you just disproved your own theory.

What I meant is that fatigue from raising the tool is dependent on overall mass for a GIVEN design/grip. I.e. I'm assuming one is holding the tool by the handle, and assuming an approx overall length and weight. My theory dissolves if these assumptions are not made.

Linear and rotational dynamics are controlled by slightly different properties, yet the two affect each other during swings. On second thought, this part could take a while to get into, so I'll wait & see if you're even interested first.
Actually there have been some good threads on it in the testing forum: Chopping Physics, andChopping Physics II. I tried starting a third thread on the subject but didn't get much interest, so feel free to bring that one back if you'd like to discuss it.

I am interested; but I think when the day is over, the good design is the one that works; physics be damned. I expect there to be some trial and error with my design. Ideas are just that: ideas.

And my point is I don't think there's any practical way to make a "machete" with the same mass distribution as a hammer. It sure wouldn't be a knife or machete any more. The hammer (and axe) works because it has a lot of mass clustered at the end of a light shaft. How are you gonna get over 3/4 of a pound of steel in the last few inches of your blade? How will you do so while keeping the rest of the blade and handle light? Because if you can't do this, it will not work like a hammer, and if you try, it will probably not work like a machete anymore, either.

For the most part, I agree. You keep trying to compare my conception to a (conventional) hatchet. I agree, a hatchet is no good on bramble/brush because you can't accelerate it fast enough. However, the concept I am trying to convey is that my design would behave like a 8oz hatchet, not a standard hatchet (which I guess to be about the same as hammers, 16 oz to 24 oz range). Now an 8oz hatchet, you could accelerate! My design is intended for brush and anything green up to 3", not wood. As to whether or not it will be a knife/machete anymore; as far as I'm concerned, if its sharp and used for brush, its a machete.

You said your approach would be to increase blade length. I agree, but my whole goal is to make something thats about 16" overall, so I've felt the need to rethink some things.

thanks

 

[Jared Stenoien]

It sounds more like a bolo to me...

 

[P.Brewster]

Sorry, I mixed your quotes with my comments in my last reply.

How do I quote bits and pieces?

thanks

 

[P.Brewster]

There are folks far more qualified than me to talk about the physics involved with chopping, but I'm interested in the subject all the same. Some thoughts-


Assuming all three are of the same basic design, then you've simply found the one that best suits your personal strength/physique. Someone who's very strong and slow may prefer the heavier one; someone wiry with cat-like speed may prefer an even lighter one.

yes, exactly.

Very astute; thanks for bringing that up. It further confirms my thoughts here...

Either one could be taken to the extreme and be less effective. There is a limit to how fast you can swing your arm regardless of the blade weight, or how heavy a blade you can still swing at reasonable speed.

I agree, which is why I am talking about a LIGHT blade, but a light blade with a good portion of its mass near the tip.

This is a little too simplistic a formula, as you noted above yourself. If your hammer had a lead handle, it still wouldn't slow down your swing very much since the weight is close to your hand. Yet power goes way down, because of the way mass distribution affects the impact mechanics.

You're right. I think there's a formula for momentum that contributes to the overall force.

Yeah, I think you just disproved your own theory.

What I meant was that fatigue is dependant on overall mass if we assume a given grip and overall length. If we drop these assumptions, the fatigue factor changes.

Linear and rotational dynamics are controlled by slightly different properties, yet the two affect each other during swings. On second thought, this part could take a while to get into, so I'll wait & see if you're even interested first.
Actually there have been some good threads on it in the testing forum: Chopping Physics, andChopping Physics II. I tried starting a third thread on the subject but didn't get much interest, so feel free to bring that one back if you'd like to discuss it.

I am interested; but I think experience and experimentation are the last word.

And my point is I don't think there's any practical way to make a "machete" with the same mass distribution as a hammer. It sure wouldn't be a knife or machete any more. The hammer (and axe) works because it has a lot of mass clustered at the end of a light shaft. How are you gonna get over 3/4 of a pound of steel in the last few inches of your blade? How will you do so while keeping the rest of the blade and handle light? Because if you can't do this, it will not work like a hammer, and if you try, it will probably not work like a machete anymore, either.

The reason I compared my design to a hammer, and not a hatchet, is because hammers are available in all different sizes and weights; whereas a hatchet is generally available in one size/weight range. Specifically, I am comparing it to a light (say 10 oz) hammer: the OVERALL mass is low, but the mass is on the tip.

I agree, a hatchet is terrible at cutting brush due to slow acceleration. I feel confident that an 8oz hatchet, on the other hand, would cut well if it was sharp etc.

thanks

ps looks like "preview post" is pretty important. sorry about the jumbled post above.

 

[kimjune01]

a knife is not a hammer, at least it shouldn't be. The balance is different. If you were to put a pommel on the lead hammer, you'd get a better swing at it and drive nails faster. To show you what I mean

this is the balance and will affect how much your wrists will work (I'm assuming that one uses his wrist to up that velocity). The weight is held by the arm, which have little to do with the impact. Speaking of impact(which is the same as momentum)

F (force) = m (mass) x v (velocity) ^2 (squared)

Force is not what drives the machete into the wood/bushes but impact
P=mv
which is the product of mass and velocity. In strict terms,

if we double the mass, we double the force. But if we double the speed, we quadruple the force.

if we double the mass, we double the impact, which is the cutting power and the same for velocity.

The impact allowed by the hammer:

As mentioned before, more weight of the hammer restricts its velocity. Why? torque. More torque is required if the center of mass is further away from the axis. Now we're getting somewhere.
What if the center of mass was somewhere along the middle? What if we take off the weight or add a counterweight? If we were to take off the weight, we would compromise impact for balance. If a counterweight is added, then neither mass nor velocity is compromised. This is possible due to the third class levers

The triangle represents the axis.
If the center of mass is closer to the axis AND a bulk of the weight is at the point of impact, then a great amount of impact(momentum) can be applied.

So, my suggestion to you is - if you want greater impact without sacrificing anything but a little arm strength, then add a pommel or some other form of counterweight to the handle end of the machete, as well as a bulk of weight at the other end.
Consider these links as a reference as you are making your first:
http://www.edcknives.com/vcom/knife_knowledge.php
http://www.cutleryscience.com/reviews/blade_materials.html#main
http://www.cutleryscience.com/reviews/reviews.html

Also, consider Khukuris as it's IMO, the best chopper known to man. I'm about to make one next week.
Good luck and have fun. and remember, safety first

 

[bikermikearchery]

The top 3 knives have accompanied me to many forests and jungles around the world. I've tried a lot of other knives and machetes, some big Bowie's and the kukris, but these knives keep working. The first and second knives are made from Leaf-spring, which is normally 5160 steel, HOWEVER some of the older WW11 area jeep springs were 1050 to 1070 type steel (already had this debate and don't care to go over it again)
The third knife is made from a farriers rasp, Which is normally 1095 steel ,HOWEVER other steels with similar property's are sometimes used instead of 1095, (already had this debate also and don't care to go over it again)
These knives are thick from 1/4" to 3/8" the blades are from 11" to 12" long. Overall length is 16" to 18" and they are convex ground. These blades are hardened but tempered back to the mid 40s more like a spring. That way they can be sharpened with a file or any smooth rock in the field.