VIBRATION

I always hear about vibration when hammering or chopping with certain tools. What is this phenomena. VIBRATION. There are two types; one is free vibration and the other is forced vibration. Forced is the type we are talking about here. It is induced by external forces. In order to dampen vibrations the natural frequency of the supporting material must be smaller or different than the disturbing or impact frequency(laymans terms of course). In mechanical devices this is done by use of springs and for example rubber padded motor mounts in cars. These things serve to reduce the vibrations transmitted to the user. How does this transfer to knives. Well let's take any knife. All steels operate at the same basic frequencies, which is a combination of density, shape,mass and size. For all intents and purposes all knives will transmit vibrations relatively equally regardless of physical differences because the differences are so slight. So how do you reduce the impact vibration. Well by means of handle material. For all intents and purposes, the more fibrous, sponge(less density) the material the more absorbent it will be. Layers of dissimilar materials also reduce vibration.

Thus take for example a full tang with any kind of handle slabs, micarta, G-10, wood,etc. The full tang will transmit the vibrations directly to the usually thin slabs and of course to your hands. Net result; OUCH! A taper tang with bone or wood handle will have to transmit the vibrations through considerably less dense/more fibrous material and thus the vibrations are reduced, not eliminated of course. This is why the Nepalese khukuri's feel to have less vibration during impact than other khukuri's.

If you are making a custom knife and you plan on doing serious chopping, but want a full tang, then you must select more than one material to dampen. For example, full tang knife with micarta slabs screwed on. What you do here if you want to reduce vibration is insert a thin layer of neoprene or kevlar sheet(less than 1/8 inch thick) and this will lessen, not eliminate, vibrations. You never see this because most people don't care about the vibrations since chopping is not their biggest concern. Of course a good shooting glove will do the same thing.

You may mention then why do kraton handled knives still hurt when I chop with them. Well, because they are usually full tang and the kraton is very thin. This offers very little vibration dampening. But hell, what do I know. I'll go back to being V.P. of humor.
 
When most people describe as knife as transmitting vibration badly they are not really describing vibration but the effects of a torque being created upon impact of the knife hitting the wood. Its the sharp slap that your hand gets that can be a problem. I would call it backlash instead of vibration.

Take a well made neutral balanced knife (neutral meaning the center of mass is at the handle/blade juncture), and using a really secure grip with a locked wrist swing, slam it as hard as you can into a piece of hardwood. Do this a couple of dozen times and notice how your palm, wrist and forearm feel. It will not be that pleasant.

Because of this a lot of people use a very open grip (with just one or two fingers actually on the handle) and snap the knife instead of swinging it. You get almost no backlash using this method and you can chop for quite sometime comfortably. Of course there is a downside and that is you can't get any great amount of power that way and its not as precise as straight swinging.

With a well made khukuri, the center of mass is far infront of the handle and its placed to get the maxium shearing effect of the blade curvature. Because of the mass being concentrated where it is, you can use locked wrist chops with great force with little discomfort from backlash.

-Cliff
 
You are right Cliff, in fact the shape of the khukuri gives you the most powerfull grip possible when you strike which goes a long way to reducing the feld forces. Vibrations are still an issue, however, and they can be painfull. But you can almost never get rid of them because you need the best compromise between handle strength and obsorbtion. If you look at some of the Gerber fixed blades like the LMF, I think, they have that padded foam handle which goes a long way to reducing the vibrations in your hand, however, the torquing effect is still there.
 
I can do all kinds of tests like that. In fact I was fooling around with pressure sensors trying to measure impacts awhile ago. In a few years I might be able to convince them to let me rewrite a few of the first year labs and bring the khukuris in. Well, I doubt that will actually happen, but you never know.

Anyway, in general, I find that the only one that can make sense out of highly tenchincal data is the people doing the testing. Personally I much prefer practical field testing to quoting say Charpy numbers although the latter type stuff can be useful.

The problem with the numbers is that they can be extreem misleading as Walt pointed out in his post in the general forum. For example CPM 420 V claims a 10 time increase over D2 in abrasion resistance (tempered to the same toughness level). However I have never heard anyone actually reporting the edge holding is anywhere near this.

-Cliff
 
My only concern with some of these incredible edge holding steels is the impact resistance as compared to say 5160 or the more ductile steels. So many seem to take toughness for granted, for the sake of edge holding. I want a combo of the two.
 
Cobalt,

I think this is where differential hardening or laminated blades comes in. Harden the cutting edge but keep the rest as soft as possible.

I wonder where Damascus steel fits into this?

Bicycle (mentioned in another tread) and chainsaw gloves have high tech vibration asorbtion materials in them. These work great. This stuff when dropped will absorb the energy and will not bounce.

For control (especially with a 20" Ang Khola) a solid grip on the handle is required. The tapered tang, differential hardening, and materials is appreciated.

Will
 
Cobalt I agree completely. You cannot ignore toughness. For any heavy use knife high abrasion resistance does not imply high edge holding anyway. If order for a blade to hold a decent bevel it has to have a very high impact toughness or else it will just chip out and leave you with a mess. Now if you are just using it for light work like a filleting knife then you can go with something very hard like CPM-15V as it will never strike rock, impact off a nail etc. CPM does offer some steels that are supposed to have both. For example CPM 3V has 4 times the impact strength of A2 and 2-3 times its abrasion resistance. The problem is that there is little practical hands on type of information out there on all the new materials. It would be very interesting to see how for example a 3V khukuri would compare to a HI model. Note the price of the 3V blade would probably be anywhere from 2-5 times the price.

-Cliff
 
Cliff, I think that out of all the steels going now 3V may have some serious promise, but, as you stated, cost will be a factor. And, also, as you stated, there is no working experiance with it and it is hard to push something that may chip. My biggest fear in knives meant for utility work is edge chipping due to brittle steel. I would almost rather do more sharpening than having a steel that chips due to extreme hardness or high carbon content.

I think that right now, I would still opt for a good heat treated A-2, M-2, 52100, D-2 etc, over the high alloy steels, since the performance of these steels is fairly predictable. If Busse ever releases the makeup of his INFI steel, this may be another option. Wouldn't it be funny if it ended up being a CPM steel.
 
Cobalt, it can't be a CPM, not one of the regular ones anyway as it has Cobalt in it. It might be related to Talonite / Stellite which are supposed to have extreem toughness and edge retention. I will be getting some CPM blades soon as well as some Talonite ones so I can check out edge durability for myself, as like you it one of my biggest concerns.

It would be interesting to run some of the new high tech steels against the performance of a known quality steel like 5160 (in the HI khukuris).

-Cliff
 
I hope everybody else understands what Cliff and Cobalt are discussing here.

I am like the kamis. If it looks like an old car spring I have an idea of what it will do as a khukuri. Anything else and it is a mystery to us.

Bill
 
Cliff, what has Cobalt in it? the Busse knife steel? I did not even know that he had publicized the constituents of his steel yet. I should be getting some of these materials soon to, so we will see.

Bill, these are high alloy steels that offer incredible mechanical advantages over the regular steels, WE THINK. They are way to costly to turn into a khukuri but for the smaller fixed blade knives they do well.
 
Check out the link in knife reviews for Wayne Goddard's edge holding test.

http://www.ameritech.net/users/knives/edge.htm

Hand forced 5160 is listed in his test.

Will
 
Cobalt, when Busse came out with the new line of basics with "modified INFI" Mike Turber commented that one of the differences between this and regular INFI was that it contained no Cobalt. See :

http://www.bladeforums.com/ubb/Forum1/HTML/001074.html

Will, those tests are very interesting and nicely done but is it just me that is very surpried at those numbers? They all seem really low to me they indicate performace levels that are very different from the properties often quoted about different blade materials. For example 5160 (HI khukuri steel), D2 and M2 all have about the same edge holding abilities and the often promoted extreem edge holders like 440V and Stellite are little better.

For comparasion Busse claims that over 1600 cuts on 1" hemp are necessary to dull a BM.

-Cliff
 
Cliff, thanks, I wonder how his line of basics is going to hold up.

Will, Cliff is right, those results do not appear correct. I have knives in Stellite, 440V, ATS, A-2 and many other steels and the 440V outlasts all the steels by a much larger margin than indicated on those tests. Also, the stellite, is still going strong. I have yet to dull it. In fact I just sharpenned it because I was getting sick of waiting for it to dull so that I could see how hard it is to sharpen. I would say that the stellite outlast the 440V by 3 to 1 in my experience. 440V outlasts my other blades easily 4 to 1. My spyderco military is still sharp after years of use as is my Hawg millenium in 440V. I don't use the Hawg that much though.

Spyderco, has an edge testing machine and has done tests on most of these materials. It would be nice to see their results.
 
Cobalt, Mike Turber is going to run a Basic against a Trail Master (and possibly an ATAK). So that should be interesting.

In regards to edge testing I never test on something as soft as wood, rope, cardboard etc. Its simply too soft and takes far too long to dull a decent steel. I usually use light metals or graphite rods.

-Cliff
 
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