This thing really just about speaks for itself.
The Mantis Gearhead would be a perfectly unassuming normal-ish liner lock folding knife if it weren't for the fact that it's a solid contender for a knife with the most overwrought opening mechanism ever. It's got a planetary gearbox in the pivot that converts the press of the lever you see there into a full 180 degree swing of the blade.
No, really.
This also makes it a one handed opener via the aid of this... mechanism... without the need for any type of spring loading. Thus it is another one of our entrants in the Very Definitely Not A Switchblade category, which is sure to annoy some legislator somewhere if only they knew about it.
This composite is downscaled quite heavily, but it gives you the idea. Note the rotation of the planetary gears and their sun ring, and movement of the lever. They're not just on there for decoration. All the little gears turn when you open it. All the little gears are used specifically to open it. There's no other way. And there is no reason to do this. It is pants-on-head loony and I love it.
The Gearhead is quite chunky, at a good 5/8" thick (not including the pocket clip). It weighs 119.2 grams (4.2 ounces), with a blade length of 2-3/4" and about 2-5/8" of usable length. The blade is pedestrian 440C steel, 0.104" thick, and presented here in this doofy tanto point. Other options, including drop point profiles and variants with brass rather than silver gears are allegedly available. But out of stock everywhere, so I have to take what I can get.
So enough about that: How it is as an actual knife?
Well, terrible.
The problem with the Gearhead is that aside from its clockpunk opening mechanism, it's otherwise just an ordinary cheap folding knife, not made to any particular standard of precision and without much thought towards usability.
The big one: It takes an incredible shove on that lever to actually open the knife. In order to turn the very short lever press into the very long opening arc, it's geared up significantly. Its gear ratio is 1:4. Not 4:1! It's not a gear reduction. It's an increase. So it takes four times as much force against the lever as it'd take to open the blade itself by hand. (I counted a lot of tiny gear teeth to bring you this info, by the way. 48 on the ring gear, 12 on the sun gear.) And since it's just an ordinary cheap liner lock knife underneath, the beginning of that lever press also has to employ enough force to overcome the little detent nub that holds the blade in the closed position.
It's kind of a thumb-buster, is what I'm getting at.
And there's no thumb stud if you'd like to open it the normal way. I'd also argue that the detent is really unnecessary, since there's more than enough friction across the pivot and geartrain to prevent the knife from flopping open in your pocket. The mechanism can't freewheel -- if the blade is moved, the gears have to move, and vise-versa.
And then, it's actually remarkably difficult to hold the knife in exactly the pose that allows you to mash the lever hard enough but not get you palm in the way, either to block the blade from moving or just grazing your palm with the tip as it passes by.
The rear of this knife has this oddball backing disk that's trying really hard to look like it needs a fancy five-pronged spanner to remove it. It's cosplaying as one of those weird retainer nuts from a Boker folding knife, perhaps. But it's fake: The disk actually spins freely and serves no purpose other than as a decorative spacer. What's actually holding it together is the normal screw head in the middle.
Also located there is the non-reversible pocket clip. The clip's very basic, but at least functional. I can see no reason it could not be mounted to the other side other than pure cost cutting in not drilling the requisite holes. It's the perfect length to go on the slab on the front side of the knife just as well as the rear, but you just can't put it there because no provision was made to do so.
Whatever. Let's see if this thing is as complicated on the inside as it looks.
Yes. Yes it is.
As expected, the geartrain drives the sun gear (in the middle of that black disk) which is attached to an axle that directly turns the blade. The blade has a semicircular slot in it that rides in a peg screwed into the liner. This is probably to ensure it doesn't wiggle much and keeps the gear teeth meshed.
The sun gear takes the full brunt of the opening force and is just peened to its axle. If this were to fail mechanically at some point, this is where I'd expect it to happen. I really would have liked to see it riding on a splined shaft instead, but let's face it -- that was never going to happen.
All of the internal gears are made of sheet steel, most likely laser or waterjet cut. The outer sun gear ring with its lever appears to be cast, with some machining work done on its inner teeth.
Oh, and you probably spotted it already: The blade rides on the cheapest, flimsiest thrust bearings I've ever seen in my life. The carriers are molded out of plastic, and I'm not entirely convinced the balls within actually turn. I think when you spin the knife everything just rides over the nubs.
The drive end of the axle is D shaped with a flat on it that engages a matching one in the blade. One thrust bearing sits on top of the blade between it and the gear stack, and the other one goes on that backer disk we looked at earlier, and explains why it spins freely. The second thrust bearing is probably unnecessary, but its thickness is accounted for in the design so you can't leave it out if you expect to tighten everything back up when you're done.
The planet gears themselves just ride on some shouldered Torx head screws. There are no other bearings or anything. The Gearhead thus comes liberally gooped up with grease from the factory, which is why it's so ugly in all my photos. Degrease it at your own peril; the whole thing would probably grind to a halt instantly if you did.
As it happens, getting the Gearhead back together is a bit of a faff. You might think it'd be possible to assemble it wrong, but that's really not so. Actually, it's even worse. It goes back together precisely one way, and if you get any of it even slightly out of place you'll find that the screw holes don't line up. The hard part therefore isn't necessarily figuring out where everything goes, but rather making sure the planet gears wind up in there in exactly the right way so that the teeth mesh and you can still get their axle screws through. I had to use tweezers. Your mileage may vary.
So the upshot of all this is that this thing isn't really a knife you can take apart and tune to perfection.
Oh, the other factor is that the geartrain is completely exposed all the time. There's no cover over it, not even a perfunctory piece of clear plastic, so every particle of grit, fiber of pocket lint, and molecule of dirt is going to find itself nestled in your gears as soon as you take this thing anywhere, with laser-guided inevitability. Taking it apart to clean it on a regular basis is not really viable, either.
The Inevitable Conclusion
If you wear a top hat, a scarf, and goggles on a daily basis, this might just be the knife for you. Otherwise, an entry level regular liner lock folder will be cheaper and arguably easier to use. And if you want fast one handed deployment for Tactical Ninja Operator purposes, a spring assist or pushbutton switchblade will be infinitely easier to use.
If you're in an area where such a thing is illegal, the Gearhead might raise eybrows as well. A lot of laws prohibiting switchblades go on to specify "spring action, gravity, or any other mechanism" and I don't think it gets much more any-other-mechanism than this.
But as we know, good, bad, and weird are not always directly related. If you're the right type of weirdo, to see this was to want one right at the start. Nothing else I said here really mattered after you saw that first picture, did it?
