25" Gelbu special: Bent on the first chop!

DannyinJapan

DannyinJapan

Joined
Oct 9, 2003
Messages
5,594
I am absolutely unconcerned about this because I know HI will make good in some way, and hey, theyve done enough for me so that I dont much care either way.
Anyhow, I went out to make the bamboo cutting video I promised, and my new 25" gelbu bent at an angle during either the first or second chop.
The edge is fine, but the whole blade is bent off to the left.

It's weird....

Do you guys think I did this with a bad chop or should the blade have been more resilient?
What should I do? Should I send it back to Yangdu?

Dan, could you straighten and retemper this for me?
 
were you chopping with your left hand Danny? how thick was the bamboo?

the reason I ask is because it looks to me like the blade bent while chopping left handed on thick bamboo, the thinner (and lighter!) Gelbu blade maybe turned a bit and momentum made it bend.

of course, it is late. I should be sleeping and I MIGHT just be babbling. :eek:
 
Woh! Man, you sure don't see that very often.

According to everything I've heard from and about HI, that shouldn't have happened. Bamboo shouldn't be any problem for a big 25" GS, I wouldn't think. See what Dan says, but I think that this might be an issue for Yangdu. But you're right. If there is indeed a problem, since this is HI, there won't be a problem for long. It will be made right, I have no doubt.

Now, you must plot your revenge upon the bamboo that has dealt you this grievous wrong! It cannot escape your justice. :D ;)

Nam
 
I was chopping three inch thick bamboo, green, with my right hand.
I made a video and sent it Satori, hoping he will post it somehow....
 
namaarie said:
It cannot escape your justice. Nam
Click to expand...

Oh dont you worry... I drug his big, blade-bending a$$ back to my apartment.
I'm going to make some kind of ninja-stick out of it...
Honestly, Id rather not bother Yangdu about it.
I like the knife, it has spirit.
It just needs a little adjustment...
Im sure it was my fault, I dont chop bamboo very often.
 
Video as received was 1.5megs, I trimmed about 500k off the beginning for the benefit of the dialup users.

Movie.

Danny, let me know if and when you want it taken down - here or via email are both fine, but I'm seldom near a computer at work. I really hate chopping up someone else's movie but it seemed in everyone's best interests to trim the beginning a bit. If you'd prefer that I put up the complete 1.5 meg movie let me know and I'll take this one down and get the original up.

I took a quick look at it in Windows Movie Maker for the frame by frame feature and couldn't really see the blade's bend until right towards the end; when Danny is showing the severed bamboo stalk the GS is visible at a spine-on point of view.

I couldn't find a particular frame where the blade was obviously bent before this. Perhaps someone else can.

My first guess would be the first cut that scrapes down the trunk. (If I'm seeing it correctly.) I would expect that to turn the edge if anything, not throw the point out to the left, but I'm hardly an expert in these matters. The second cut looked fine to me but again I'm not an expert. Hopefully someone else can spot something that I've missed.
 
The first chop, a glancing blow, looks to me like it would be the culprit. Lots of torque was put on that long blade at that point.:(=sad.

DIJ if you will, see if you can't wedge the blade between two unmovable objects reasonably close together and see if you can straighten the blade.
Then if you did, take it back out and try it again. I'll just about bet 10 dollars to a donut that if it hits properly it won't bend again but...:confused:

The problem with these long narrow blades is that they aren't hardened far enough through the blade to make the blade as stiff as it could/would be otherwise.
It would be interesting to see what an etch shows up on that blade.

Satori is there a trick in making the viewer run frame by frame?

Edit:
When you watch the movie instead of watching the blade watch the stalk of bamboo. It appears to move four inches at least to my old tired eyes, some of you youngsters may be able to see it better.
If that had been a solid tree it probably would've sent a shock up into your arm DIJ.
 
Yvsa said:
It would be interesting to see what an etch shows up on that blade.
Click to expand...

Great idea, etch the blade and see what the temper looks like. I'm sure everyone is curious to find out.
 
Ill try to etch it, but I dont really know how.
Also, Im not sure If I should "do" anything to it at thispoint, seeing as I dont know what to do with it.
Should I send it back, send it to Dan or try to fix it myself...
As to torque on the second cut, both cuts were the same, but I made the angle more acute for cut #2.
 
Even of the cut wasnt perfectly executed, one would expect more sturdines from 1/2´´ thick piece of steel.....

I m surprised... THat looks like if the bend starts in the sweet spot?
 
right there, in fact.
its weird, like the spine was too soft and the hard edge wanted to go its own way...
 
That glancing blow would bend a lot of swords. It looked like you hit too close to the tip. I'd just hammer it straight, or leave it alone and chop some more :)
Bamboo is very tough on blades, it has a very hard shell and a springy core... thus all the zen allusions to bending like it. Plus it is smooth so there isn't anything for the blade to "grab" if it's a slightly off-angle blow.
How much does the blade weigh? I'd definitely temper it. I'd rather see the points hardened. If you break off a point, you still have a knife. A knife that bends enough can be useless, though.
Thankfully your Gelbu still looks quite usable.
 
Mr.BadExample said:
That glancing blow would bend a lot of swords. It looked like you hit too close to the tip. I'd just hammer it straight, or leave it alone and chop some more :)
Bamboo is very tough on blades, it has a very hard shell and a springy core... thus all the zen allusions to bending like it. Plus it is smooth so there isn't anything for the blade to "grab" if it's a slightly off-angle blow.
How much does the blade weigh? I'd definitely temper it. I'd rather see the points hardened. If you break off a point, you still have a knife. A knife that bends enough can be useless, though.
Thankfully your Gelbu still looks quite usable.
Click to expand...

i've heard alot of stories about proper laminated steel katana's being bent or broken by a slight error in technique cutting bamboo, much better to try it on a pile of criminals or serfs & see how many you can cut thru, or tatami mats if you lacking crims and don't see a convenient serf...
 
Perhaps blade of that size and weight needs bit more hardened and springy material everywhere. It would be interesting to strip it down and send it to Daniel Koster or someone else to clay harden it leaving only lesser part of blade soft /bit more on the sweetspot.
That and little tweaking and will be good. I think that one of that wicked hamons would look nice.....

Perhaps also the blade itself is too heavy being this size and it would use fuller such as is on Foxy folly to lighten it up and take a load off the sweetspot.

I have clay hardened my seax and its brutish thing, but the unhardened area is rather big to my taste.
 
Do you have a vise Danny?

If so, this would probably be the best way to straighten it. Take three pieces of round rod. Nails will work, or maybe even a wood dowel. Take two of the round pieces, and attach them to one of the jaws of the vise using tape or something. Put one on each end of the vise jaw. Take the third rod and attach it to the middle of the other vise jaw.

Now when you put something in the vise and tighten it, the three rods will act as pressure points, and the middle rod will bend the thing inward. Place the khuk in the vise, with the spot where it is bent on the middle rod. Tighten the vise a little at a time, then release the pressure and check to see if the blade is straight. If not, tighten it a little more. Keep going until the blade is straight.

I'll try to draw up a little picture so you see exactly what I mean.

here is a picture, the red line represents the blade:

straightening%20jig.JPG


when the jaws are tightened, you will reverse the bend in the knife. You will have to bend it a little past the point where it is straight, then when you release the pressure, it will return to straight.

I've bent a couple of thin blades from bad cuts on wood, and this method seems to work the best for getting them straight again.
 
Good technique Danny...awesome power and speed. I'd say it was the first "wrong" swing...I bet had it bit into the bamboo it would have done fine, but all of the energy you generated was too much for the non-hardened part. I'd say that you are spoiled by that horse-chopping sword you have.

I'll honestly say that I'm impressed...I can't imagine doing that on purpose.

As you say...Yangdu will make it right one way or another.

.
 
Bamboo is tough stuff man. The last two places I lived we had some growing and it wasn't like that stuff you're cutting. Not even half that thick and it was tough to cut if you didn't connect just right. I don't think I could have made that cut without a lot of practice. As far as the bent blade, I don't know that much about the physics or whatever, but all the suggestions seem sound. I'd love to hear what Dan Koster has to say about it.
 
!?!

Only HI I ever bent was the tip of a much-used BAS; my bad for dropping it. Straightened up with vise/hammer.

The 25" Malla wouldn't bend if Superman chopped a pier piling with it- it couldn't. Same thickness as 20" AK, IIRC. Never owned a Gelbu Special; does the back hollowing weaken it? It sure has heck doesn't with an Ang Khola.

Ad Astra :confused:
 
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