Bent 25" Gelbu Update

Svashtar

Svashtar

Joined
Dec 28, 2003
Messages
4,793
Well, I worked out a deal to get Danny's bent 25" gelbu, and with Khukuri Monster's excellent advice I worked on it today and was very pleased with the results.

I chocked it up in a 7" Wilton woodworking vise, and used hardwood dowels in place of the steel rods khuk monster recommended, and then tightened it up _very_ carefully. I half-expected the thing to snap, and at one point had it at least 1" out of alignment in the direction opposite the bend. I'm sure I probably could have gone several inches before anything happened, but I didn't want to find out as I know I was putting a lot of stress on the long blade.

I tightened it in the worse area of the bend, and then loosened the vise and rolled the blade both backwards and forwards along the dowels, and then repeated the process each time.

The bottom line is that the blade is over 2" deep at the bent area, and because of both the distal taper, and the taper from the spine to the edge, it bent in different ways at the time of the damage.

My main concern was getting the cutting edge straight, and that worked out perfectly. In one spot the spine is still maybe a sixteenth out of alignment, but I can't tweak that so easily without also changing other parts of the blade, so I'm going to resist my perfectionist nature and leave it the hell alone. The cutting edge is straight now, as well as most of the blade itself in that area, and that's what matters as far as using the knife.

I think the damage happened because the blade is not really that sharp. No kidding, it is a tribute to Danny's second swing that he was able to get through that bamboo with this edge IMO. The slightly off center first cut combined with the dull edge turned the knife and caused the damage. At least that's what I think, I _could_ be wrong! :D

Here's some of my typically awful pics. The first two show the setup with the vise that I probably repeated in different areas a dozen times, the third shows the knife laying flat on my anvil, so that you can see the blade is straight now, and the last fuzzy one is the blade held straight out, with the formerly bent part of the blade hilighted.

My only question now, is how that bending and rebending back will affect the integrity of the blade. Hopefully it can still be used safely for some cutting tasks.

Next I have to use a burnisher on the blade, as the bend put a little ding in the edge that has to be rolled out, and then I'm going to sharpen the whole thing the way Yvsa showed me at the SWKK with my Cherokee Rose, with a DMT sharpener. Should be a nice big razor when I'm finished.

This is a nice knife, and I'm glad this worked out for everybody.

Regards,

Norm
 
Really nice, Norm.

old quote:

"Being able to bring the tool back to usability is part of the joy of having a quality tool. In a sense, the owner shares creation with the maker of the blade, and they join together to create a functional implement to achieve a purpose."


You share creation!
 
That looks great, you did a perfect job as far as I can see. I am really an amateur at cutting plants, nobody ever taught me that. If I bent it because I dont know how to cut plants properly, then I wouldnt be surprised.
I thought it was sharp enough for bamboo, but then again, i am a terrible sharpener.
I am sure you will fulfill its potential more than I ever could here in Japan , Norm. Im glad it ended up at your house.
 
Svashtar said:
My only question now, is how that bending and rebending back will affect the integrity of the blade. Hopefully it can still be used safely for some cutting tasks.
Click to expand...

I can't be sure about this. An engineer or somebody who understands strength of materials would probably know. But here's what I think. Whenever you bend a piece of steel so far that it doesn't spring back, it creates stress.

If you were to bend it a full 90 degrees back and forth it might fail quickly. But you are only bending a couple of degrees, so it shouldn't stress the steel significantly (that is to say, don't worry about it), especially since it has only been bent a few times.
 
Norm...the bending *may* even produce a bit of work hardening and stiffen the effected area...making it better than it was.

I agree...we saw in the video how much force Danny produced with his swing...what would those blows do with a sharp blade?

.
 
Being an ME, bending is cold working. The problem you get is that you do not have a homogeneously hardened blade. You now have different phases along the temper line. This can cause stress fractures eventually.
The thing that the Khuk's have going for them is that they are so soft to begin with that a little cold working may not have much effect. If the cold working did any damage you are likely to notice it on the edge of the knife at the bend. If you notice chipping, then the thing is finished. If not you should be ok.
 
great work Norm.


Personally, if it were me, I'd test it out a few times - maybe start off with some soft 2x4 pine. If it bends, straighten it back out and hang it on the wall.


Can you take a pic from the side to show us where the bend began? Have you etched it? If you could do that first, perhaps it might show that the bend is beyond the hardened zone (my guess, anyway).
 
Daniel Koster said:
great work Norm.


Personally, if it were me, I'd test it out a few times - maybe start off with some soft 2x4 pine. If it bends, straighten it back out and hang it on the wall.


Can you take a pic from the side to show us where the bend began? Have you etched it? If you could do that first, perhaps it might show that the bend is beyond the hardened zone (my guess, anyway).
Click to expand...

Thanks Dan. I could take a relatively (for me) decent pic of the side and point to where the bend _was_, but there is nothing there physically now that I can see to indicate where it was. What there is, is a slight dimple right at the edge, where the hardened area bent slightly, so it is in the hardened zone. (Cobalt, thanks for the great info; the edge was damaged, but that was in the initial hit. The rework did not appear to have any new adverse affects.) Picture the blade width going from bottom to top, hard to soft, with the top portion bending the most and the bottom the least, but it did technically bend.

It is the exact kind of damage you see on a khuk edge when chopping and you hit a rock or something and get a ding. I planned on burnishing it a bit to realign it the fraction it needs, and then when I sharpen it it should not be visible. You have to look pretty hard to see it now, and I haven't started work on it yet.

I wish I knew how to etch it. An etch would show how much of hardened area there was there. Maybe the bend was at a soft spot or gap in the hardening, which in this case would actually be a help. Since this is kind of an experimental blade anyway, I wouldn't mind using it as my first etch attempt today. Save me a search. Do you have any tips as to the best way to bring out the hamon? I know there are natural ways to do it with mustard or something, but would just prefer to buy a bottle of "HI Khukuri Etching Liquid" (or equivalent) and get 'er done that way. :D

Thanks,

Norm
 
I know Dan and others use etchant from Radio Shack, but I'm cheap and lazy. I wash the blade with hot soapy water, then douse it with Everclear as a degreaser, then soak it in vinegar. Nothing fancy and it doesn't produce a deep etch, but it does etch enough to clearly see the hamon.

.
 
Have you checked how thick the blade is? What does the knife weigh?
I didn't watch the video, but thought that the GS was a knife with a thick blade -- I have a small panawal AK with a 7/16" thick blade. I can't imagine how you could bend a blade that thick....without trying very, very hard.

The larger knife makes for a long blade and lots of leverage.
 
I have found that CLR delivers a nice gray etch, plus it removes any rust spots;) Seems to work well on both satin and mirror polished finishes.

Jake
 
The Satori Rust Remover Etch works well for quick and dirty etches, merely to see what's to be seen.

Degrease the blade, rinse it under the hottest water your tap can produce (this will heat the blade and aid in etching), paint on some rust remover, count to twenty, rinse it off and neutralize. Do it outdoors.

The result will not be pretty but the hamon will be very visible.

I suppose that it will remove rust as well but I haven't used it for this purpose in a long time. ;)

Whatever you use, post some pics. I'd love to see what the heat treat looks like on that GS.
 
arty said:
Have you checked how thick the blade is? What does the knife weigh?
I didn't watch the video, but thought that the GS was a knife with a thick blade -- I have a small panawal AK with a 7/16" thick blade. I can't imagine how you could bend a blade that thick....without trying very, very hard.

The larger knife makes for a long blade and lots of leverage.
Click to expand...

Arty, the knife is 25" long and 29 oz. I haven't check the thickness of the blade but there was a tremendous amount of inertia in that swing, and it hit something very hard. It hit just forward of the middle downward curve, and the last 8-9" of the blade just kept on going. It's a tribute to the strength of the blade that it didn't bend even more. As it was, Danny was still able to fit it easily into the scabbard to ship to me. Of course, now it fits much better... (-:

Regards,

Norm
 
Steely_Gunz said:
I have found that CLR delivers a nice gray etch, plus it removes any rust spots;) Seems to work well on both satin and mirror polished finishes.

Jake
Click to expand...

Jake, that's the CLR in the grey plastic jug, right? The "industrial strength" stuff? I have some CLR kitchen foam stuff, but I can't see that doing anything.

Thanks,

Norm
 
Norm...honest...either lemon or vinegar will do it. Prep the blade as described and then make sure you neutralize the acids with baking soda /water (make a paste of it and smear it all over the blade) after getting the degree of etch you want to stop the etching process, rinse under hot water, dry and re-oil.

Dan uses the Radio Shack circuit board etchent and an acetone rinse to "pop" the hamon...but I don't know as I am cheap and lazy.

.
 
If anyone else wants to know how to bend their khukuris, here`s the secret.
When you begin your cut, dont let your shoulders drop. Turn from the waist like an action figure and bend your knees deeply at the same time. No arm strength is needed. Jut use the power of your body turning from the waist and dropping vertically (from your knees bending)
that oughtta do it.
 
Danny...when we asked you how a Ninja would defeat a khukuri, we meant fighting someone armed with a khukuri...

Not defeating the khukuri itself!
 
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