Knifemakers: What can your custom knives do? (..time to brag on the ladies)

D

DCM

Joined
Aug 28, 2006
Messages
56
I'm interested in hearing stories, true and even w/ some embellishments.. For example, Ed Schempp has been rumored to have cut over a hundred 1" hemp ropes at once with his knife. This is probably an exageration.. but, a knife designed for a specific task. (I think the actual # is around 9 or 10?) The important point to me, is that the knife is made to optimize efficiency in a task that is accomplished with remarkable results. That's what I want to hear about.
Thanks,.
David
 
I've cut hundreds of ropes; one at a time. A few years ago at the North Knife Collectors Show Competition, I cut 11. Bill Burke, Greg Beeman, Matt Diskin, Michael Rader have all cut 8 or more in competition. Warren Osborn cut 9 in Waxahachie.

I've used a design based on a Philippine Bolo used in an area that grows rattan, Manilla hemp, and sugar cane. The blade has a concave curve to keep the material from slipping off the end of the knife. I use a diamond shaped blade to keep the mass toward the edge and have rotational balance. By having mass of the blade before the cut, the knife self aligns during the cut and doesn't twist in your hand and strike the medium with it side, like many triangular geometries.

Edge geometries are tested to failure and tuned for the piece of steel in the blade.

Wayne Goddard and Ed Fowler have preached testing for years, and have developed methodology. Check out their previous writing in Blade magazine.
 
I saw a Scagle that was double ground, then Ed Schemp's triangular blade design, (another description of double ground, kind of) then one made by Rudy Ruana in the 1930's, finally I heard the message. I talked to Ed, he shared his thoughts with me and now I see more. There is much to learn about lady knife!
 
As for me.....well, the ones i have actually completed will cut various things most of the time.....hey....it's a start:D
 
A couple of my favorite Eds...:thumbup:

I've been trying to figure out how the shape of the blade help aligns the cut for rotational balance but haven't quite grasped the concept yet. Do you mean the way the front of the blade, toward the tip, angles down below the line of the handle?
 
In rotational balance I'm talking about the balance from edge to spine not the end to end or tip to handle balance.

The false edge on the back of the knife takes weight away from the spine of the knife and moves the mass toward the edge, at least from the back of the blade to more in the center of the blade.

Let me define a convex blade as a bellied blade and a concave blade as a hooked blade.

Think of pushing a bicycle with no rider. Bikes have a positive rake on the front fork. When you push a bike it wobbles and crashes. Now turn the front fork around 180 degrees. Now you have a negative rake on the front forks. Now push the bike and it will roll smoothly until it loses speed. The convex curve is like a positive rake it put the mass of the blade behind the edge in some cases a couple of inches. The concave curved blade is like the negative raked bicycle, now the mass of the bike leads the tire or the mass of the blade leads the edge. The vector of cut has to have the edge and the spine aligned. In a concave cuved blade the mass of the blade and the edge are much closer together on the vector of the cut. When you are cutting stationary targets the difference is not as noticable as when the target moves and the vector of the cut has to be changed in cut then the concave blade has less of a moment arm to torque the blade in your hand.

Rotation balance can be achieved with a false edge or a fuller which lightens the spine of the knife moving the balance point forward toward the edge.

The concave blade shortens the moment arm on the force vector, a bellied or convex blade lengthens the moment arm. Triangular geometry puts mass toward the back of the blade lenghthening the moment arm. The diamond shaped blade shortens the moment arm. These are the concepts in design that affects the succuss of the cut...Take Care...Ed
 
Thanks for the explanation, Ed. I know axe guys talked about this a lot, saying the axe should be "center balanced"; i.e., the weight of the cutting edge and poll should line up with the center of the handle, or it will want to twist in your grip when swung. When I finally obtained a big HI khukri, these concepts became immediately obvious in use. It has a lot of weight out there on the blade which drops below the centerline from the handle.

But I think it may also be worth pointing out that you'd want to do it differently depending on whether you want to cut with just the tip area, or further down the blade.


Ed Schempp said:
Let me define a convex blade as a bellied blade and a concave blade as a hooked blade.
Click to expand...

If ya don't mind, I'll use a saber and sickle when talking about your ideas of a convex or concave blade, respectively.

With my khukri, if I chopped about halfway down the blade in the deep part of the curve (using the portion of the edge shaped like a sickle), the weight further out below the edge would help carry it forward in the cut and keep things aligned. However, if I tried chopping near the tip, the opposite effect happened. Now, the blade was acting like the "positive rake" you mentioned with a bicycle. Now, the mass was way behind the edge, and the blade wanted to twist severely.

And, as mentioned above, the mass distribution matters not just on impact, but when you start the swing, too. If the mass is below the centerline from your grip, ("forward rake", or sickel) it will want to twist in your hand a bit during the swing, making it harder to get the cut aligned to begin with. With a saber type blade, with the mass lagging behind your hand ("negative rake"), it will want to stay more in line with a straight swing, but can still cause problems with a curving swing.

Also, it's not just the mass, but the geometry involved. With the edge further below the centerline like a sickle, it forms a longer lever against your grip. And since it's actually leading ahead of the grip, can cause more twising. With a saber shape, even if the edge is the same distance from the centerline, now it's behind your grip, and will want to stay aligned better- "negative rake". This can have just as much effect as the mass.

So, if I'm understanding you correctly, I pretty much agree with your ideas. But I still think it really depends on whether you want to use the belly or the tip for more of your cutting.

Ed Schempp said:
Rotation balance can be achieved with a false edge or a fuller which lightens the spine of the knife moving the balance point forward toward the edge.
Click to expand...

Perhaps the best compromise between the two would be a straight symmetrical double edged blade like a European sword or dagger. :)
 
All things being equal and using the sweet spot of the blade to cut, usually in the middle of the blade; the shorter the moment arm the less torque. Using the tip of a Katana or a saber puts much of the mass the belly ahead ot the cut and helps align the cut. Depends on what part of the blade you intend to work to do the cut. Thank you for delineating the concept Possum. It is just math and physics...Take Care...Ed
 
Yeah, and thanks.
Ed Schempp said:
...using the sweet spot of the blade to cut, usually in the middle of the blade...
Click to expand...
This comment helps me understand where you're coming from. The "sweet spot" goes all the way to the tip of my big bowies, and this is where I do most of my cutting. So, this gives me a different perspective. :)
 
:thumbup: , I'm w/ Jose, I'd like to attend that seminar. Just the explanation leaves me :confused:, .. I do get the basic ideas,.. i think.

Thanks Ed, for advancing the "art" of the performance knife. ...both Ed's, :)
David
 
There is area of Physics termed the resolution of component forces. To me this was the most dynamic aspect of high school and college physics. The dynamics apply to any kind of knife you want to make and bring emperical understanding to knife design.
 
You must log in or register to reply here.
Back
Top