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Old 03-17-2003, 10:46 PM
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Switchblade mechanisms.

I hope this isn't going to trip the "illegal activities" wire.

There are two kinds of automatic knives I've seen. One is the side-opening "traditional" switchblade. The other is a "front opening" where the blade snaps out of the handle on a straight line from butt to hilt when the button is pushed toward the hilt. When the button (switch, I guess, really) is pushed toward the butt, the blade retracts into the housing.

I've given it some thought, I've googled until I'm hitting the concealed weapons policies of small midwestern universities, and I can't for the life of me figure out the mechanical details of the front opening switchblade.

Ignorance is present. Fight it!
Old 03-17-2003, 10:52 PM
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The type of knife you're describing is called a stiletto. I'm not exactly sure how it works either, but knowing the correct name might help you out.
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Old 03-17-2003, 11:04 PM
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I take that back. Googling "stiletto" shows me a bunch of thin-bladed side-opening knives. I'd have sworn that's what I'd heard them called. I know the kind you mean, though, and I'll keep looking.
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Old 03-17-2003, 11:18 PM
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Are you thinking about a gravity knife?
Old 03-17-2003, 11:18 PM
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I had a stiletto once...the mechanism was something like this...two springs..one slack when the other one was tight; depressing button releases/depresses pin which allows tight spring to pull in opposite direction. the pin went through a hole in the part of the blade which was below the blade proper. the pin was cut at an angle which is kind of like a non-deadbolt lock on a door lock which would allow the blade to slide along until it could lock into place.
Old 03-17-2003, 11:24 PM
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Quote:
This type of automatic is a bit more delicate, since it works off of a double spring action, whereas the standard side openerís work on a single spring action.
From [url=http://admiralsawesomeknives.com/automaticknifeinstructions.htm[this page.[/url]

Doesn't give much more info, but there are a few clues. We know know it's called an OTF knife in the trade, and it uses springs. That along with the details of how to recover from a "loose blade" condition, I came up with an idea. Here's my guess on the mechanics: With the blade retracted, the bottom spring is compressed, and the blade is locked in place. Pushing the lever forward compresses the top spring and then unlocks the blade, allowing the bottom spring to push it up until it lock in it's "out" position. Pulling the lever back does the opposite, compressing the bottom spring and allowing the top spring to push it back until it locks in its "closed" position.
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Old 03-17-2003, 11:35 PM
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The type of knife you descirbe is not generally considered a stiletto. A stiletto, historically, is a knife with a very sharp point. Not necessarily an edged weapon. One potential use for these stilettos was to puncture armor in the medieval times. For example, a stiletto may have a triangular 'blade', with none of the edges sharpened, but tapering to a sharp, strong point.

Now the front opening switchblades are generally termed simply 'front-openers'. The usualy method of action is a flat piece of spring steel that has been bent into a zigzag shape. This is placed in the handle of the knife, and then some form of trigger is added towards the front of the knife (usually a lever type trigger). To withdraw the blade either you place the point against a hard object and push until the trigger catches, or there may be a small post mounted to the moving end of the spring that allows you to pull back until the trigger catches.

Very simple mechanisms, but hard to describe in words.

Here's a link to one more modern front-opener, the Microtech HALO (try a Google):

http://chris.cc/halo.htm
Old 03-17-2003, 11:43 PM
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I can't get a handle on how two springs could repeatedly counteract one another, or how moving the lever would compress one of the springs.

What we have here is a failure to find a diagram.

I know there are such things, but since I don't have a credit card or a desire to spend a day or two waiting for Ragnar Benson's book to be shipped to me I can't find one.

handsomeharry, I think you may have helped some with the angled pin thing.

Q.E.D., the stilleto question is a different thread. To me it's a fixed blade knife with a very thin blade (often triangular in cross section) which could only be used to stab somebody. I've read that they were a combination tool for self defence and cannon maintenance that became associated with the criminal classes, and the word may just have migrated to mean a long thin bladed cool-looking knife which is primarily useful for criminal types.

Hup the Fool, that looks like a side opening switchblade to me. Gravity knives, at least around here, are knives that can be opened by flicking your wrist to apply centrifugal force to the blade.

I saw a variation on the front opening switchblade at a gun show once. It had a fixed blade with a plastic guard that snapped up and down into the housing. They wouldn't let me take it apart, though. Some people are just mean.
Old 03-17-2003, 11:45 PM
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That'd be an OTF or "out the front" knife.

Here's a link to a mechanism detail & discussion.

-AmbushBug
Old 03-17-2003, 11:50 PM
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Melraidin, we had a bit of a simulpost there, but unless I have totally slipped a gear there are some out there that snap out and snap back in, without the need to push against a hard object or pull on a post.
Old 03-17-2003, 11:57 PM
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No go on the link, AmbushBug.
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Old 03-18-2003, 12:42 AM
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Heh. That guy's going to feel important tomorrow.
Old 03-18-2003, 12:49 AM
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From AmbushBug's link (which now works):
Quote:
Here's what happens. When you push the button forward, you are stretching the springs as the rear plate is hooked on the end of the blade. When it pushes forward enough to move the liner lock out of the way, the blade is "slingshotted" forward until the front liner lock springs in and holds it open. When you slide the button backwards, the spring is hooked on the stud on the blade and stretches until the flaired shape at the front pushes the liner lock out of the way and the blade is "slingshotted" back in the handle. There is no tension on the spring when the knife is in the open or closed position. It is only when you are moving the button that the springs are stretched, and this is cocking the knife until the blade is released. I hope this makes sense to you, it does to me!
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