Idea to reduce handle cracking

X

X-Head

Joined
Nov 8, 1999
Messages
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I think most, if not all, cracks that develop in horn and wood handles are caused by the handle material shrinking around the rat tail tang (or conversely, by the rat tail tang expanding inside the handle material and the handle material refusing to expand with it).

Yes, most of us have already figured out that much. But here's what I think would help reduce this, and it would require a very minor design change. I know that the purpose of forging the rat tail tang with a squarish, angled cross section is to prevent rotation of the handle, but why not forge the rat tails with an oval cross section, or rectangular cross section with the edges rounded somewhat? Rotation of the handle material would still be impossible, and you would thereby eliminate the 4 hard edges around the rat tail, which are the primary sources of handle cracking. I think it was Will Kwan who noted in an old HI thread that he had noticed that all the handle cracks he has seen have been at (I'm paraphrasing here) "X" locations on the handle rather than "+" locations (if you're looking down the handle from the butt). Uncle may remember reading the above comments by Will. This is consistent with my experience, and also with the axiom that sharp interior corners generally are weaker than interior curves, speaking in terms of stress handling. So if you have a rat tail tang with an oval or rounded rectangle cross section, and (EQUALLY IMPORTANT) a tang hole in the handle material that is oval or rounded rectangle to match, I think you would greatly reduce handle cracking in both horn and wood.

I know the kamis can forge such a tang. The question is, can they bore such a hole in the handle to match?

I'm just a layman, and not a very bright one at that. I know there are a lot of great minds here. Any comments on this hairbrain idea?

[This message has been edited by X-Head (edited 03-05-2001).]
 
Sounds to me like an idea worth testing. So the good news is you've picked up your first backer; the bad news, I'm afraid, is I don't know squat about matters involving materials fatigue. I'm interested in what some of our hands-on and engineering-type thinkers have to say about this.
 
Well, this is where my idea runs smack into the brick wall of reality.
wink.gif


Oh well, Uncle. I had to try, but I understand your predicament. The possibilities of offending the master kamis by presuming to tell them how to make a better khukuri, and the misunderstandings arising out of the translation and passing the instructions along verbally through 2 or 3 people are strong likelihoods.

Mochiman1, I appreciate your comments on this.

 
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Doing something like that might help, but I really doubt it.
The problem stems from natural products that can shrink or grow depending on the humidity and the steel being pretty much an immovable force. And when something that can shrink conflicts with something immovable something is going to happen to relieve the stress.
I believe the only sure fix would be to stabilize the wood or horn handles by impregnating them with another material the same as the stabilized wood and other natural products that are generally used by modern knife makers. And that would add a considerable cost whereas a cracked handle can be easily fixed with some super glue or epoxy or in the worst case replaced by Terry or yourself if you have any skill at all.

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"VEGETARIAN".............
Indin word for lousy hunter.
 

Question for Uncle Bill and others who own newer khukuries:

Has the handle cracking problem been helped/solved by better aged horn yet? I know awhile back there was talk of Gelbu(?) tracking down a few hundred lbs of well cured horn, but I don't remember what ever came of that.

Rob
 
Thanks, Yvsa. All comments appreciated.

As for Maui Rob's comment, I'm sure that cured horn would help at least some. What I'm wondering is, could Gelbu, rather than searching for cured horn and paying more for it, just buy extra horn from his regular sources, and set aside what isn't immediately needed to be cured at BirGorkha? Perhaps this is what he is already doing.
 
I agree, Uncle; that's not a bad percentage. Besides, if it weren't for cracked handles, there would hardly be any UBDOTD's!
 
Horn is a natural material. As such it is prone to acting a bit funny from time to time. One of the best things about working with horn for handles is that it is a natural material, and you never know what is under all extra material. The worst thing about working with horn for handles is that it is a natural material, and sometimes it will do the unexpected.
 
Making the tang oval will help prevent cracking somewhat. There will no longer be a sharp corner to start a crack that is produced by hard use.

It will probably not help to prevent cracks due to shrinkage. However the crack location will be more random.

Will
 
An oval tang would require a very accurate oval hole or adhesive filler to avoid handle play. The solution to me would be to keep the current tang shape, but make the hole oversized (no contact between the tang and handle). The gap between the handle and the tang would be filled with a somewhat compliant adhesive filler. I'm not sure what this would be. Maybe an epoxy with a ground neoprene filler. This would reduce stress and stress concentration "hot spots" between the tang and the handle.

 
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