How Does an OTF Knife Work?

How Does an OTF Knife Work?

How Does an OTF Knife Work?

Single Action OTF and Double Action OTF Knives

Out the front pocket knives are some of the most useful, convenient and frankly badass knives you can buy. But did you know there are actually two different types of OTF knife? And do you have any idea how they actually make the blade shoot out the front automatically, time and time again? If not, you’re about the learn how - we’ll cover the mechanism used in both single and double action OTFs, and which is best for you.

How to Operate an Out the Front Knife

While understanding how it works under the hood can be confusing, actually operating an OTF knife is pretty simple.

For a double action OTF, you simply push the switch up to eject the knife, and pull it back to retract it. Simple as that. While some knives have switches on the side of the handle, and others have them on the face, the operation is the exact same, and doesn’t require instruction.

Single action OTFs take a few more steps, but are still pretty self-explanatory. Ejecting the knife is usually the exact same as with a DA knife - you push the switch. But retracting the knife requires you to release the blade from its extended position using a release lever. Then you have to manually slide back the blade, sometimes with a different switch than the one used for ejection. And last, it is common for SA OTFs to have safeties, which you can use to allow/prevent the blade from ejecting.

While this isn’t terribly complicated, single action OTFs can have up to 4 different touch points, whereas double action OTFs just have one. 

All that said, operating the knife is the easy part - you’re here to learn how it actually works, which is what we’ll cover next.

The OTF Knife Mechanism

Whichever kind of OTF you’re using, it almost certainly operates using a spring mechanism, which is the version we’ll be explaining here. However, the way a single action knife uses its spring is different from that of a double action. In short, SA OTFs use a spring “one way” to eject the knife and then the spring is reset manually, whereas DA OTFs use a spring for both ejection and retraction actions.

Single Action OTF Mechanism

Single Action OTF

In a closed position, a single action OTF has a compressed spring that’s pushing against a notch in the blade (or an extended spring that’s pulling on the blade). It’s held compressed by a release mechanism, which pushes against the blade to prevent it from ejecting. 

The knife’s switch is used to release the blade, allowing the spring to expand (or contract) quickly, which in turn sends the blade shooting out the front of the knife.

Once the blade is extended, the blade is locked in place by a locking mechanism that prevents the blade from sliding back into the handle.

To retract the blade, the lock must be released - sometimes using the same switch used for ejection, but other times the knife has an independent blade release. Once it is released, the blade must be manually retracted into the handle using a sliding switch. 

Double Action OTF Mechanism

Double Action OTF

A double action OTF uses its spring a little differently. The spring is attached to two clips, which in turn are meant to catch the knife at two points - one at the flat back of the blade, and one at a protrusion at the base of the blade meant just for this purpose. The spring is housed in a sliding mechanism that helps release the knife when the switch is flipped.

The knife’s switch works by stretching the spring, pulling the attachment point at one end of the blade. The blade is initially held back by a spring-loaded gate digging into a notch in the blade’s base, preventing it from sliding forward. But a groove in the sliding mechanism gradually folds this gate out of the way, until the blade is released all at once, causing the spring to contract, pulling the blade forward quickly out of the front of the knife.

The blade is locked in place by an identical gate at the opposite end of the handle, facing the opposite direction. This one presses on the flat, back end of the blade to prevent it from sliding back into the handle.

Unlike an SA knife, retracting the blade on a DA OTF uses the same mechanism as ejection. The switch again extends the spring and causes the a groove in the sliding mechanism to put pressure on the locking gate, until it folds just enough to let the blade get by. At which point the spring violently contracts, pulling the blade quickly back into the knife’s handle.

DA OTF Diagram

Safety Mechanism

Many OTF knives have safety mechanisms to prevent the blade from accidentally ejecting. But these usually work very differently for SA and DA out the front knives.

Single action OTFs with safeties usually have an external safety switch. This switch controls an internal locking mechanism which either holds the blade in place or releases it, depending on whether the safety is engaged. Pretty simple.

This kind of mechanism is less common on double action OTFs, though. Instead, when you hear about a DA “safety”, what is often meant is the knife’s “ability” to fall loose when the blade bumps into something upon ejection.

While this is a nice feature to have, it’s not actually a separate “safety” mechanism, but in fact just an inevitable result of how the blade operates. 

Unlike an SA knife, where the spring sees the blade through all the way to full extension, a DA knife’s spring “slings” the blade, relying on momentum to carry it all the way forward into the locked position. So if anything is in its way, the momentum will be stopped and the blade won’t be able to eject fully. This “safety” can be reset by fully extending the blade, manually, so that it is caught by the locking mechanism, and tension can be put on the spring again.

… and more

These are just the fundamentals of how each type of knife works. In reality, every manufacturer has their own spin on how to optimally engineer these knives, and there are endless variations, like switch positioning, safety mechanisms, advances in locking and release technologies, etc, that all impact the knife internals. We’ve definitely oversimplified things here. However, this guide should give you the basic knowledge to begin to understand any OTF knife that you take apart.

Comparison: SA vs DA OTF Knife

Now knowing how each of these knives work, which is better? The answer, of course, is it depends.

Once you see how the blade mechanisms work, it is clear that in general a SA knife is going to be more reliable, in terms of blade deployment and locking in place, since it doesn’t rely on the blade’s momentum like the DA knife does. But on the other hand, a DA knife is much more convenient and easier to use one handed, since it doesn’t require manual retraction of the blade.

Of course, this is assuming that the knives being compared are of similar build quality. A wide range of OTF knives are available, from $10 knives to $1000+. In general, you can assume that more expensive knives are higher quality, with more reliable materials and mechanisms. So in that case a $200 DA OTF is likely to be more reliable than a $30 SA OTF.

In general, though, we’d recommend a single action OTF for uses where you need the blade to deploy super reliably under various conditions, and where you need the blade to lock in place ultra-securely. This includes uses like tactical, self defense, cutting tough materials, and durable utility blade / work knife uses.

And double action OTFs would be better for daily use, situations where you need to frequently deploy/retract the blade, and where convenience is otherwise a factor.

That said, we’ll reiterate that the reliability trade-offs with a DA knife decrease the higher the quality of knife you get. For that reason, our preference would be to use a high end double action OTF to get the “best of both worlds”, if your budget allows for it.

Where to buy single action and double action OTF knives?

So now you know the answer to "How Does an OTF Knife Work?" And you should have an idea of which type of OTF would fit your needs. Now you just need to find your knife.

Whichever OTF style you use, you can find plenty of options, at a range of price points, on our Out the Front Knife page, at UppercutTactical.com. 

Uppercut Tactical is an online retailer that specializes in tactical gear - specifically, OTF knives. We are a small business based in DFW, Texas and we value preparedness and personal responsibility. 

The knives demo’ed in this article:

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