Tang pins...again

GTAsteel

GTAsteel

Joined
Oct 24, 1999
Messages
781
Again as I plot the eventual construction of my own bali I have another question for you all... How is the tang pin attached to the blade? I can think of a few ways of going about it but how does, say benchmade do it?

I have also, if i recall correctly heard of tang pins failing. Are they falling out? What are some of the problems that you have seen in tang pins?

Thanks for humoring.
 
I think they just jam em in there (press fit or something). I recently had to return mine to Bbenchmade to have the tang pin replaced because the service department at Benchamde told me that I couldn't do it myself without some serious equipment.
 
The best way is to make the pin slightly oversized and dip it in liquid nitrogen to shrink it as close to the same size as the tang pin hole. In this frozen state, press the pin through the tang pin hole. As the pin warms up to room temperature, it'll expand and lock into place. A good knowledge of metallurgy is defintely helpful.

Forcing the pin in via hammering or hydralic presses will stress the tang ping hole, and could cause fractures in the steel.

Tony
 
BM's pins have a vertical rib kind of knurling that makes them a press fit into the handles.
 
Originally posted by tonyccw
The best way is to make the pin slightly oversized and dip it in liquid nitrogen to shrink it as close to the same size as the tang pin hole. In this frozen state, press the pin through the tang pin hole. As the pin warms up to room temperature, it'll expand and lock into place.
Tony
Click to expand...

I was thinking more along the lines of heating the undersized whole in the blade prior to heat treating.
 
Originally posted by GTAsteel
I was thinking more along the lines of heating the undersized whole in the blade prior to heat treating.
Click to expand...
That's fine as long as you realize you'll be tempering the tang pin to the same rockwell as the blade. Not something I would suggest. Those pins are going to take a lot of punishment, and should be a little softer. Differential metals would probaly solve this, but then you're stuck with figuring out which metal will be the best candidate.

Liquid nitrogen and a dewar aren't that hard to find purchase. The press and gig required to hold the assembly in place can also be readily set up.

Tony
 
If the hole in the blade than contracts too much around the tang ping it can fracture; I think that a combination of liq. nit. and a "rib" around the pin would work best, but im no expert.
 
Originally posted by hogman
If the hole in the blade than contracts too much around the tang ping it can fracture;
Click to expand...
The trick is the tang pin size. Too large and it will apply too much stress to the tang pin hole. Ribbing isn't necessary, as you don't really need that much oversizeing for the tang pin to hold. We're talking maybe .25mm. It's just a matter of friction. The liquid nitrgen bath will not shrink the metal that much as we're not talking about a large mass of loose material. Steel is fairly dense.

Tony
 
Originally posted by tonyccw
That's fine as long as you realize you'll be tempering the tang pin to the same rockwell as the blade
Tony
Click to expand...

True... much softer do you think it should be? It wouldnt be to hard to put a pin in out of a non hadening steel, or one that will harden up alittle, so I would think. You think that manipulation would realy put enough stress on a pin ( plan on a pretty think one) to damage it even at the same hardness of the blade?

Very interesting.....
 
Originally posted by GTAsteel
You think that manipulation would realy put enough stress on a pin ( plan on a pretty think one) to damage it even at the same hardness of the blade? Very interesting.....
Click to expand...
You're slamming the handle into the tang ping everytime you open the handle. If the handle is light and made of a soft material, like the SWAT aluminums, not much of an issue as the mass/weight is minimal. However, should you decide to put one of Eric's (Mer's) handles, then I would put the stress into consideration. It should be softer as to not transfer the stress of the impact of the handles to the tang.

Tony
 
Originally posted by tonyccw
It should be softer as to not transfer the stress of the impact of the handles to the tang.

Tony
Click to expand...

Good point, hadn't thought about it like that. Im thinking Stainless steel handles.
 
Originally posted by GTAsteel
Good point, hadn't thought about it like that. Im thinking Stainless steel handles.
Click to expand...
Glad to help. Just want to see you finish the damn thing:D .

Tony
 
Originally posted by joemamma12
what type of metal should i use? could i just get a nail and dip it in liquid nit.?
Click to expand...
You could, but needle bearing rollers are probably better choices. At least with those you can find out the critical information; RC, tempering, steel composition, and demensions. They're made to very high tolerances.

Tony
 
Originally posted by tonyccw
Glad to help. Just want to see you finish the damn thing:D .

Tony
Click to expand...

Speaking of wich, If anyone has any ideas or lessons learned form such an endevor, I'd love to hear them!
 
Originally posted by GTAsteel
Speaking of wich, If anyone has any ideas or lessons learned form such an endevor, I'd love to hear them!
Click to expand...
After spending the better part of 3 years trying to get one done, with all the mechanical drawings and materials allocated, I was overwhelmed with the small amount of tolerances it took to prevent me from making it look and work well. On top of which, my grind lines were horrible.

If you leave everything squared, and start rounding off for asthethics, it'll work fine. A square balisong is easy. Once you get to the tapering of the handles, the placement of the latch, and the asthetics of the knife open, it gets hard. And this is coming from a guy that studied mechanical engineering. My hat goes off to anyone that can pull off a really beautiful functional one.

The one thing I did learn. Get a real good drill press with dead centering. Where the tang meets the handle, everything has to fit perfectly. You can get sloppy everywhere else, except the latch.

We are, of course talking about a BM custom level output, not like a Jag or Bear here, right?

Tony
 
I don't think that having a 65 Rockwell tang pin would be any problem at all (I certainly don't think it would shatter). Even the bearing steel you mentioned is pretty hard stuff Tony.

The problem lies in the relationship between the tang pin on the blade and the tang pin cups on the handles. My 42's tang pin got a bit squashed from manipulation resulting in poor open lockup. :( If the tang pin where harder this would not have happened. The only time you don't want a hard tang pin is if the handles are soft (i.e. Zamak:barf: ) I wish BM would have made the tang pin from Titanium like the handles, that way you wouldn't have a difference in hardness (however the handles are cast 6/4, the pin would be from solid bar stock.)

By the way, I fixed my squashed tang pin by rotating it in the tang about 25 degrees. Open lockup is now tighter than it was when I first got it.;)

OH AND HEY TONY, LOOK AT OUR NUMBER OF POSTS!!! WE'RE TIED:D
 
How'd this get duplicated? :confused: Sorry, frivilous post.:(

Ha Ha now I'm one up on you Tony!;)
 
Originally posted by 7Cain
I don't think that having a 65 Rockwell tang pin would be any problem at all (I certainly don't think it would shatter). Even the bearing steel you mentioned is pretty hard stuff Tony.
Click to expand...
Retempering those pins to be a little softer than the blade isn't an issue if you knew the steel composition (which is something you'll never find from a nail). Obiviously, making your own tang pin would be the best since you then are picking your own steel and controlling the pin size. Needle bearing sounded like a good choice because you can get them made up to your specs by lots of little machine shops.

Originally posted by 7Cain
The problem lies in the relationship between the tang pin on the blade and the tang pin cups on the handles.
Click to expand...
Yes, but you can always make the handles softer than the tang pin. So in terms of hardness, the hardest would be the blade, then tang pin, and last the handle. Even with a softer handle, you'll still have to deal with the impact stress of the handle hitting the tang pin, and the tang pin transferring that stress to the blade. A softer tang pin will cushion that stress a bit to avoid stressing the blade.

Originally posted by 7Cain
By the way, I fixed my squashed tang pin by rotating it in the tang about 25 degrees. Open lockup is now tighter than it was when I first got it.;)
Click to expand...
OK, here's where I have a problem with the way BM makes the tang pins. If you are able to rotate it, then it's not 100% tight against the blade, and there's a minute gap between the tang pin and the blade. The will cause the tang pin to bounce against the blade's tang pin hole. In my books, that's a bad design. Using the freezing method, you'll get a as perfect to 360 degree mating, with little to no gaps as possible, for maxium friction lockup, for all 3 axis (no sliding up or down, no rotation, and no wobble). Plus there would be no need to peen. Peening the tang pin into the blade, ala the Jag, causes too many issues with the handle relationship you and Eric were referring to.

Originally posted by 7Cain
OH AND HEY TONY, LOOK AT OUR NUMBER OF POSTS!!! WE'RE TIED:D
Click to expand...
Not anymore.... besides, you've had a 3 month head start.. OK, so I'm a blabbermouth...:D :D

Tony
 
You must log in or register to reply here.
Back
Top