Has this ever happened to you--tang shearing???

Chiro75

Chiro75

Joined
Feb 4, 1999
Messages
5,786
Okay...I am testing a knife for a maker that will remain anonymous at this time. The knife has scales that are held on by bolts. The fit wasn't perfect in the rear of the knife and I had to dismantle the knife to see what the prioblem was (bolts too long and weren't snugging up the scales to the tang). I replaced the scales and tightened up the bolts and on one of the four bolts I heard and felt a little grittiness. I've been a bike shop mechanic for over three years and work around threaded parts constantly, most of which are VERY fragile, so I have a good touch when it comes to not overtightening things. I figured it was a little grit in the threads, but boy was I wrong!
Anyway, I was testing the knife in the kitchen today and of course water went into the gap between the tang and the scales, so I had to dismantle it again to dry it, and I figured while I was at it I would go ahead and just grind a bit off each of the bolts to improve the scale's fit. I got it apart, dried it out, but when putting it back together one of the rear bolts didn't want to thread in, so I removed the scale and noticed at that point that some of the metal around the rear hole in the tang had sheared clean off and was still threaded around the bolt! When you look at the hole in the tang, which was not countersunk, there is a round wedge shaped cutout where that metal had previously been. It looked like the hole was now countersunk and it was nearly perfectly round! I figure what happened is that a stress riser formed around that hole and caused the metal, which is D-2, to be brittle, resulting in it shearing away with the light force of the screw's threading motion.
Anyway, what do you think happened?

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My Custom Kydex Sheath page:
http://www.geocities.com/CollegePark/Lab/1298/frames.html
Palmer College of Chiropractic
On Two Wheels
agocs_s@dd.palmer.edu
Madpoet (Mel Sorg, Jr.) Tribute page:
http://www.geocities.com/CollegePark/Lab/1298/madpoet/main.html

 
Chiro, hardened D-2 should eat the bolts. That it sheared off means it was badly if at all heat treated. It sounds like marginal workmanship at best.

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Jerry Hossom
www.hossom.com

[This message has been edited by GaKnife (edited 03-01-2000).]
 
I'd check the material. As Jerry said, D2 should chew through almost anything, and the neat trick about heat treating D2 is that if you screw it up, it's usually TOO hard, and even at full hardness, it wouldn't behave the way you described. If it wasn't D2, and was heat treated like D2, it would do that.
 
Fellas, the knife comes from a reputable maker, and the other tests indicate it is heat-treated just fine, at least at the blade. I've emailed the maker and am waiting a response, so we'll see. I'll do a brass rod test and see what happens...

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My Custom Kydex Sheath page:
http://www.geocities.com/CollegePark/Lab/1298/frames.html
Palmer College of Chiropractic
On Two Wheels
agocs_s@dd.palmer.edu
Madpoet (Mel Sorg, Jr.) Tribute page:
http://www.geocities.com/CollegePark/Lab/1298/madpoet/main.html

 
I didn't mean to imply that the maker was bad, I'm just theorizing that he may have been misinformed as to his steel content. Many people take it on faith that a steel recieved is what they're told it is. That's often all we have to go on, but I'd be interested in seeing that steels spark.

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Oz

Always remember what to do to them if they can't take a joke.

Check out my egostistical homepage!
http://www.freespeech.org/oz/
 
I'd be interested in hearing the response. Even anealed D2 should strip the bolt. That the bolt didn't fit properly was another matter, and one which you should reasonably expect to be corrected.

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Jerry Hossom
www.hossom.com
 
Well, I did a brass rod test and the edge is perfect. I scraped a file over the edge of the tang and it skittered right off with barely even shining the metal up. It's definitely hardened right, at least judging by those crude methods. I have also chopped, sliced, stabbed, twisted, and torqued this knife without holding back and it performs very well. Something weird is definitely going on! As far as whether it is D-2 or not, I think it is. I have lots of D-2 knives and when they are wet they get this charecteristic patina that I know pretty well. None of my other knives do it unless they are D-2. This one did the same. I THINK it is D-2, but can't be sure. Regardless of that, the knife performs very well and it is properly hardened. Any other explanantions for what could cause this? Would the threads in the holes weaken the metal significantly during heat treat?

------------------
My Custom Kydex Sheath page:
http://www.geocities.com/CollegePark/Lab/1298/frames.html
Palmer College of Chiropractic
On Two Wheels
agocs_s@dd.palmer.edu
Madpoet (Mel Sorg, Jr.) Tribute page:
http://www.geocities.com/CollegePark/Lab/1298/madpoet/main.html

 
Check the "metal " around the bolt.... sounds like the hole was countersunk and the "metal " that sheared off is liquid steel or a steel epoxy.

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There is no such thing as "good enough", either your work is good or it is not. How is your work?
SGT BLADES www.therockies.com/hagar/
 
There was a trick I heard, that if you had already heat treated the blade and wanted to thread the holes in the tang, you could enlarge the holes and weld in a bit of softer metal, then tap the holes.
Could this have been the problem?
 
OK, how about Tang WAY too hard, thread badly cut or hole undersize, bolt cross threaded. If the holes were drilled before hardening then there might have been HT stress cracks around lip of hole or at least a conditionof brittleness, coarse grain that coupled with binding of bad thread/cross thread let go.
 
The knife is D2, heat-treated to 60Rc, and tested. I know because I'm the maker! Fox Creek had the correct reasoning. The problem reared its' ugly head once before, and I have since begun to slightly chamfer the holes before tapping. I believe the sharp threads were brittle (10-32, btw)and the edge where the screws first bite could flake off if the screw hit cross. I use an alloy screw, and the D2 has torn up plenty of them. This knife and the other I spoke of (two of my earlier blades) had a very brittle lip around the hole. Sharp edges are week, and this was indeed the cause. This probably could have been eliminated if I had simply shortened the screws, but in my haste to get Chiro the knife, I left them long. A lesson learned.

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Chris Hatin

http://www.hatintec.com

"Are you ready for the defendant, Judge?"
"Yup. Bring the guilty bastard in."
 
As an experienced knifemaker I should well know there are technical issues and time constraints that often come in conflict with making the knife we know how to make. I forgot that here, and rushed to shoot off my mouth about what I assumed to be the problem. For that I owe everyone an apology and and especially humble apology to Chris.

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Jerry Hossom
www.hossom.com
 
Thanks, Jerry. I should not have let a knife go out that may have developed a problem, especially on that would fall into the detructive hands of Chiro!!
wink.gif
(jk Steve) The great thing about Bladeforum's is that we can all learn and grow here. I know I have! Thanks again.


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Chris Hatin

http://www.hatintec.com

"Are you ready for the defendant, Judge?"
"Yup. Bring the guilty bastard in."
 
Hey, I'm a real lightweight on my knives! When I test something I don't want to beat it up because I ususally own it already!
smile.gif
We figured out what the problem is, so that's good. Goes to show that everyone, regardless of their experience, can learn a thing or two. FWIW the couple of things I had to point out negatively about the knife are all resulting from the rush that Chris was experiencing, which was actually a funny story in and of itself that you will have to read with the review! I should have it done by the end of the night and ready for everyone to read within a day or two. At least I didn't light the damn thing on fire or throw it around (Cliff)!
wink.gif

The bottom line iss that despite these problems, I woudln't hesitate to buy a knife from Chris.

------------------
My Custom Kydex Sheath page:
http://www.geocities.com/CollegePark/Lab/1298/frames.html
Palmer College of Chiropractic
On Two Wheels
agocs_s@dd.palmer.edu
Madpoet (Mel Sorg, Jr.) Tribute page:
http://www.geocities.com/CollegePark/Lab/1298/madpoet/main.html

 
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